NOMMU: Make VMAs per MM as for MMU-mode linux

Make VMAs per mm_struct as for MMU-mode linux.  This solves two problems:

 (1) In SYSV SHM where nattch for a segment does not reflect the number of
     shmat's (and forks) done.

 (2) In mmap() where the VMA's vm_mm is set to point to the parent mm by an
     exec'ing process when VM_EXECUTABLE is specified, regardless of the fact
     that a VMA might be shared and already have its vm_mm assigned to another
     process or a dead process.

A new struct (vm_region) is introduced to track a mapped region and to remember
the circumstances under which it may be shared and the vm_list_struct structure
is discarded as it's no longer required.

This patch makes the following additional changes:

 (1) Regions are now allocated with alloc_pages() rather than kmalloc() and
     with no recourse to __GFP_COMP, so the pages are not composite.  Instead,
     each page has a reference on it held by the region.  Anything else that is
     interested in such a page will have to get a reference on it to retain it.
     When the pages are released due to unmapping, each page is passed to
     put_page() and will be freed when the page usage count reaches zero.

 (2) Excess pages are trimmed after an allocation as the allocation must be
     made as a power-of-2 quantity of pages.

 (3) VMAs are added to the parent MM's R/B tree and mmap lists.  As an MM may
     end up with overlapping VMAs within the tree, the VMA struct address is
     appended to the sort key.

 (4) Non-anonymous VMAs are now added to the backing inode's prio list.

 (5) Holes may be punched in anonymous VMAs with munmap(), releasing parts of
     the backing region.  The VMA and region structs will be split if
     necessary.

 (6) sys_shmdt() only releases one attachment to a SYSV IPC shared memory
     segment instead of all the attachments at that addresss.  Multiple
     shmat()'s return the same address under NOMMU-mode instead of different
     virtual addresses as under MMU-mode.

 (7) Core dumping for ELF-FDPIC requires fewer exceptions for NOMMU-mode.

 (8) /proc/maps is now the global list of mapped regions, and may list bits
     that aren't actually mapped anywhere.

 (9) /proc/meminfo gains a line (tagged "MmapCopy") that indicates the amount
     of RAM currently allocated by mmap to hold mappable regions that can't be
     mapped directly.  These are copies of the backing device or file if not
     anonymous.

These changes make NOMMU mode more similar to MMU mode.  The downside is that
NOMMU mode requires some extra memory to track things over NOMMU without this
patch (VMAs are no longer shared, and there are now region structs).

Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Mike Frysinger <vapier.adi@gmail.com>
Acked-by: Paul Mundt <lethal@linux-sh.org>

1 files changed, 664 insertions, 296 deletions

diff --git a/mm/nommu.c b/mm/nommu.c
index 23f355bbe262..0d363dfcf10e 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -6,7 +6,7 @@
  *
  *  See Documentation/nommu-mmap.txt
  *
- *  Copyright (c) 2004-2005 David Howells <dhowells@redhat.com>
+ *  Copyright (c) 2004-2008 David Howells <dhowells@redhat.com>
  *  Copyright (c) 2000-2003 David McCullough <davidm@snapgear.com>
  *  Copyright (c) 2000-2001 D Jeff Dionne <jeff@uClinux.org>
  *  Copyright (c) 2002      Greg Ungerer <gerg@snapgear.com>
@@ -33,6 +33,28 @@
 #include <asm/uaccess.h>
 #include <asm/tlb.h>
 #include <asm/tlbflush.h>
+#include "internal.h"
+
+static inline __attribute__((format(printf, 1, 2)))
+void no_printk(const char *fmt, ...)
+{
+}
+
+#if 0
+#define kenter(FMT, ...) \
+        printk(KERN_DEBUG "==> %s("FMT")\n", __func__, ##__VA_ARGS__)
+#define kleave(FMT, ...) \
+        printk(KERN_DEBUG "<== %s()"FMT"\n", __func__, ##__VA_ARGS__)
+#define kdebug(FMT, ...) \
+        printk(KERN_DEBUG "xxx" FMT"yyy\n", ##__VA_ARGS__)
+#else
+#define kenter(FMT, ...) \
+        no_printk(KERN_DEBUG "==> %s("FMT")\n", __func__, ##__VA_ARGS__)
+#define kleave(FMT, ...) \
+        no_printk(KERN_DEBUG "<== %s()"FMT"\n", __func__, ##__VA_ARGS__)
+#define kdebug(FMT, ...) \
+        no_printk(KERN_DEBUG FMT"\n", ##__VA_ARGS__)
+#endif
 
 #include "internal.h"
 
@@ -46,12 +68,15 @@ int sysctl_overcommit_ratio = 50; /* default is 50% */
 int sysctl_max_map_count = DEFAULT_MAX_MAP_COUNT;
 int heap_stack_gap = 0;
 
+atomic_t mmap_pages_allocated;
+
 EXPORT_SYMBOL(mem_map);
 EXPORT_SYMBOL(num_physpages);
 
-/* list of shareable VMAs */
-struct rb_root nommu_vma_tree = RB_ROOT;
-DECLARE_RWSEM(nommu_vma_sem);
+/* list of mapped, potentially shareable regions */
+static struct kmem_cache *vm_region_jar;
+struct rb_root nommu_region_tree = RB_ROOT;
+DECLARE_RWSEM(nommu_region_sem);
 
 struct vm_operations_struct generic_file_vm_ops = {
 };
@@ -400,129 +425,174 @@ asmlinkage unsigned long sys_brk(unsigned long brk)
         return mm->brk = brk;
 }
 
-#ifdef DEBUG
-static void show_process_blocks(void)
+/*
+ * initialise the VMA and region record slabs
+ */
+void __init mmap_init(void)
 {
-        struct vm_list_struct *vml;
-
-        printk("Process blocks %d:", current->pid);
-
-        for (vml = &current->mm->context.vmlist; vml; vml = vml->next) {
-                printk(" %p: %p", vml, vml->vma);
-                if (vml->vma)
-                        printk(" (%d @%lx #%d)",
-                               kobjsize((void *) vml->vma->vm_start),
-                               vml->vma->vm_start,
-                               atomic_read(&vml->vma->vm_usage));
-                printk(vml->next ? " ->" : ".\n");
-        }
+        vm_region_jar = kmem_cache_create("vm_region_jar",
+                                          sizeof(struct vm_region), 0,
+                                          SLAB_PANIC, NULL);
+        vm_area_cachep = kmem_cache_create("vm_area_struct",
+                                           sizeof(struct vm_area_struct), 0,
+                                           SLAB_PANIC, NULL);
 }
-#endif /* DEBUG */
 
 /*
- * add a VMA into a process's mm_struct in the appropriate place in the list
- * - should be called with mm->mmap_sem held writelocked
+ * validate the region tree
+ * - the caller must hold the region lock
  */
-static void add_vma_to_mm(struct mm_struct *mm, struct vm_list_struct *vml)
+#ifdef CONFIG_DEBUG_NOMMU_REGIONS
+static noinline void validate_nommu_regions(void)
 {
-        struct vm_list_struct **ppv;
+        struct vm_region *region, *last;
+        struct rb_node *p, *lastp;
 
-        for (ppv = &current->mm->context.vmlist; *ppv; ppv = &(*ppv)->next)
-                if ((*ppv)->vma->vm_start > vml->vma->vm_start)
-                        break;
+        lastp = rb_first(&nommu_region_tree);
+        if (!lastp)
+                return;
+
+        last = rb_entry(lastp, struct vm_region, vm_rb);
+        if (unlikely(last->vm_end <= last->vm_start))
+                BUG();
+
+        while ((p = rb_next(lastp))) {
+                region = rb_entry(p, struct vm_region, vm_rb);
+                last = rb_entry(lastp, struct vm_region, vm_rb);
+
+                if (unlikely(region->vm_end <= region->vm_start))
+                        BUG();
+                if (unlikely(region->vm_start < last->vm_end))
+                        BUG();
 
-        vml->next = *ppv;
-        *ppv = vml;
+                lastp = p;
+        }
 }
+#else
+#define validate_nommu_regions() do {} while(0)
+#endif
 
 /*
- * look up the first VMA in which addr resides, NULL if none
- * - should be called with mm->mmap_sem at least held readlocked
+ * add a region into the global tree
  */
-struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr)
+static void add_nommu_region(struct vm_region *region)
 {
-        struct vm_list_struct *loop, *vml;
+        struct vm_region *pregion;
+        struct rb_node **p, *parent;
 
-        /* search the vm_start ordered list */
-        vml = NULL;
-        for (loop = mm->context.vmlist; loop; loop = loop->next) {
-                if (loop->vma->vm_start > addr)
-                        break;
-                vml = loop;
+        validate_nommu_regions();
+
+        BUG_ON(region->vm_start & ~PAGE_MASK);
+
+        parent = NULL;
+        p = &nommu_region_tree.rb_node;
+        while (*p) {
+                parent = *p;
+                pregion = rb_entry(parent, struct vm_region, vm_rb);
+                if (region->vm_start < pregion->vm_start)
+                        p = &(*p)->rb_left;
+                else if (region->vm_start > pregion->vm_start)
+                        p = &(*p)->rb_right;
+                else if (pregion == region)
+                        return;
+                else
+                        BUG();
         }
 
-        if (vml && vml->vma->vm_end > addr)
-                return vml->vma;
+        rb_link_node(&region->vm_rb, parent, p);
+        rb_insert_color(&region->vm_rb, &nommu_region_tree);
 
-        return NULL;
+        validate_nommu_regions();
 }
-EXPORT_SYMBOL(find_vma);
 
 /*
- * find a VMA
- * - we don't extend stack VMAs under NOMMU conditions
+ * delete a region from the global tree
  */
-struct vm_area_struct *find_extend_vma(struct mm_struct *mm, unsigned long addr)
+static void delete_nommu_region(struct vm_region *region)
 {
-        return find_vma(mm, addr);
-}
+        BUG_ON(!nommu_region_tree.rb_node);
 
-int expand_stack(struct vm_area_struct *vma, unsigned long address)
-{
-        return -ENOMEM;
+        validate_nommu_regions();
+        rb_erase(&region->vm_rb, &nommu_region_tree);
+        validate_nommu_regions();
 }
 
 /*
- * look up the first VMA exactly that exactly matches addr
- * - should be called with mm->mmap_sem at least held readlocked
+ * free a contiguous series of pages
  */
-static inline struct vm_area_struct *find_vma_exact(struct mm_struct *mm,
-                                                    unsigned long addr)
+static void free_page_series(unsigned long from, unsigned long to)
 {
-        struct vm_list_struct *vml;
-
-        /* search the vm_start ordered list */
-        for (vml = mm->context.vmlist; vml; vml = vml->next) {
-                if (vml->vma->vm_start == addr)
-                        return vml->vma;
-                if (vml->vma->vm_start > addr)
-                        break;
+        for (; from < to; from += PAGE_SIZE) {
+                struct page *page = virt_to_page(from);
+
+                kdebug("- free %lx", from);
+                atomic_dec(&mmap_pages_allocated);
+                if (page_count(page) != 1)
+                        kdebug("free page %p [%d]", page, page_count(page));
+                put_page(page);
         }
-
-        return NULL;
 }
 
 /*
- * find a VMA in the global tree
+ * release a reference to a region
+ * - the caller must hold the region semaphore, which this releases
+ * - the region may not have been added to the tree yet, in which case vm_end
+ *   will equal vm_start
  */
-static inline struct vm_area_struct *find_nommu_vma(unsigned long start)
+static void __put_nommu_region(struct vm_region *region)
+        __releases(nommu_region_sem)
 {
-        struct vm_area_struct *vma;
-        struct rb_node *n = nommu_vma_tree.rb_node;
+        kenter("%p{%d}", region, atomic_read(&region->vm_usage));
 
-        while (n) {
-                vma = rb_entry(n, struct vm_area_struct, vm_rb);
+        BUG_ON(!nommu_region_tree.rb_node);
 
-                if (start < vma->vm_start)
-                        n = n->rb_left;
-                else if (start > vma->vm_start)
-                        n = n->rb_right;
-                else
-                        return vma;
+        if (atomic_dec_and_test(&region->vm_usage)) {
+                if (region->vm_end > region->vm_start)
+                        delete_nommu_region(region);
+                up_write(&nommu_region_sem);
+
+                if (region->vm_file)
+                        fput(region->vm_file);
+
+                /* IO memory and memory shared directly out of the pagecache
+                 * from ramfs/tmpfs mustn't be released here */
+                if (region->vm_flags & VM_MAPPED_COPY) {
+                        kdebug("free series");
+                        free_page_series(region->vm_start, region->vm_end);
+                }
+                kmem_cache_free(vm_region_jar, region);
+        } else {
+                up_write(&nommu_region_sem);
         }
+}
 
-        return NULL;
+/*
+ * release a reference to a region
+ */
+static void put_nommu_region(struct vm_region *region)
+{
+        down_write(&nommu_region_sem);
+        __put_nommu_region(region);
 }
 
 /*
- * add a VMA in the global tree
+ * add a VMA into a process's mm_struct in the appropriate place in the list
+ * and tree and add to the address space's page tree also if not an anonymous
+ * page
+ * - should be called with mm->mmap_sem held writelocked
  */
-static void add_nommu_vma(struct vm_area_struct *vma)
+static void add_vma_to_mm(struct mm_struct *mm, struct vm_area_struct *vma)
 {
-        struct vm_area_struct *pvma;
+        struct vm_area_struct *pvma, **pp;
         struct address_space *mapping;
-        struct rb_node **p = &nommu_vma_tree.rb_node;
-        struct rb_node *parent = NULL;
+        struct rb_node **p, *parent;
+
+        kenter(",%p", vma);
+
+        BUG_ON(!vma->vm_region);
+
+        mm->map_count++;
+        vma->vm_mm = mm;
 
         /* add the VMA to the mapping */
         if (vma->vm_file) {
@@ -533,42 +603,62 @@ static void add_nommu_vma(struct vm_area_struct *vma)
                 flush_dcache_mmap_unlock(mapping);
         }
 
-        /* add the VMA to the master list */
+        /* add the VMA to the tree */
+        parent = NULL;
+        p = &mm->mm_rb.rb_node;
         while (*p) {
                 parent = *p;
                 pvma = rb_entry(parent, struct vm_area_struct, vm_rb);
 
-                if (vma->vm_start < pvma->vm_start) {
+                /* sort by: start addr, end addr, VMA struct addr in that order
+                 * (the latter is necessary as we may get identical VMAs) */
+                if (vma->vm_start < pvma->vm_start)
                         p = &(*p)->rb_left;
-                }
-                else if (vma->vm_start > pvma->vm_start) {
+                else if (vma->vm_start > pvma->vm_start)
                         p = &(*p)->rb_right;
-                }
-                else {
-                        /* mappings are at the same address - this can only
-                         * happen for shared-mem chardevs and shared file
-                         * mappings backed by ramfs/tmpfs */
-                        BUG_ON(!(pvma->vm_flags & VM_SHARED));
-
-                        if (vma < pvma)
-                                p = &(*p)->rb_left;
-                        else if (vma > pvma)
-                                p = &(*p)->rb_right;
-                        else
-                                BUG();
-                }
+                else if (vma->vm_end < pvma->vm_end)
+                        p = &(*p)->rb_left;
+                else if (vma->vm_end > pvma->vm_end)
+                        p = &(*p)->rb_right;
+                else if (vma < pvma)
+                        p = &(*p)->rb_left;
+                else if (vma > pvma)
+                        p = &(*p)->rb_right;
+                else
+                        BUG();
         }
 
         rb_link_node(&vma->vm_rb, parent, p);
-        rb_insert_color(&vma->vm_rb, &nommu_vma_tree);
+        rb_insert_color(&vma->vm_rb, &mm->mm_rb);
+
+        /* add VMA to the VMA list also */
+        for (pp = &mm->mmap; (pvma = *pp); pp = &(*pp)->vm_next) {
+                if (pvma->vm_start > vma->vm_start)
+                        break;
+                if (pvma->vm_start < vma->vm_start)
+                        continue;
+                if (pvma->vm_end < vma->vm_end)
+                        break;
+        }
+
+        vma->vm_next = *pp;
+        *pp = vma;
 }
 
 /*
- * delete a VMA from the global list
+ * delete a VMA from its owning mm_struct and address space
  */
-static void delete_nommu_vma(struct vm_area_struct *vma)
+static void delete_vma_from_mm(struct vm_area_struct *vma)
 {
+        struct vm_area_struct **pp;
         struct address_space *mapping;
+        struct mm_struct *mm = vma->vm_mm;
+
+        kenter("%p", vma);
+
+        mm->map_count--;
+        if (mm->mmap_cache == vma)
+                mm->mmap_cache = NULL;
 
         /* remove the VMA from the mapping */
         if (vma->vm_file) {
@@ -579,8 +669,115 @@ static void delete_nommu_vma(struct vm_area_struct *vma)
                 flush_dcache_mmap_unlock(mapping);
         }
 
-        /* remove from the master list */
-        rb_erase(&vma->vm_rb, &nommu_vma_tree);
+        /* remove from the MM's tree and list */
+        rb_erase(&vma->vm_rb, &mm->mm_rb);
+        for (pp = &mm->mmap; *pp; pp = &(*pp)->vm_next) {
+                if (*pp == vma) {
+                        *pp = vma->vm_next;
+                        break;
+                }
+        }
+
+        vma->vm_mm = NULL;
+}
+
+/*
+ * destroy a VMA record
+ */
+static void delete_vma(struct mm_struct *mm, struct vm_area_struct *vma)
+{
+        kenter("%p", vma);
+        if (vma->vm_ops && vma->vm_ops->close)
+                vma->vm_ops->close(vma);
+        if (vma->vm_file) {
+                fput(vma->vm_file);
+                if (vma->vm_flags & VM_EXECUTABLE)
+                        removed_exe_file_vma(mm);
+        }
+        put_nommu_region(vma->vm_region);
+        kmem_cache_free(vm_area_cachep, vma);
+}
+
+/*
+ * look up the first VMA in which addr resides, NULL if none
+ * - should be called with mm->mmap_sem at least held readlocked
+ */
+struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr)
+{
+        struct vm_area_struct *vma;
+        struct rb_node *n = mm->mm_rb.rb_node;
+
+        /* check the cache first */
+        vma = mm->mmap_cache;
+        if (vma && vma->vm_start <= addr && vma->vm_end > addr)
+                return vma;
+
+        /* trawl the tree (there may be multiple mappings in which addr
+         * resides) */
+        for (n = rb_first(&mm->mm_rb); n; n = rb_next(n)) {
+                vma = rb_entry(n, struct vm_area_struct, vm_rb);
+                if (vma->vm_start > addr)
+                        return NULL;
+                if (vma->vm_end > addr) {
+                        mm->mmap_cache = vma;
+                        return vma;
+                }
+        }
+
+        return NULL;
+}
+EXPORT_SYMBOL(find_vma);
+
+/*
+ * find a VMA
+ * - we don't extend stack VMAs under NOMMU conditions
+ */
+struct vm_area_struct *find_extend_vma(struct mm_struct *mm, unsigned long addr)
+{
+        return find_vma(mm, addr);
+}
+
+/*
+ * expand a stack to a given address
+ * - not supported under NOMMU conditions
+ */
+int expand_stack(struct vm_area_struct *vma, unsigned long address)
+{
+        return -ENOMEM;
+}
+
+/*
+ * look up the first VMA exactly that exactly matches addr
+ * - should be called with mm->mmap_sem at least held readlocked
+ */
+static struct vm_area_struct *find_vma_exact(struct mm_struct *mm,
+                                             unsigned long addr,
+                                             unsigned long len)
+{
+        struct vm_area_struct *vma;
+        struct rb_node *n = mm->mm_rb.rb_node;
+        unsigned long end = addr + len;
+
+        /* check the cache first */
+        vma = mm->mmap_cache;
+        if (vma && vma->vm_start == addr && vma->vm_end == end)
+                return vma;
+
+        /* trawl the tree (there may be multiple mappings in which addr
+         * resides) */
+        for (n = rb_first(&mm->mm_rb); n; n = rb_next(n)) {
+                vma = rb_entry(n, struct vm_area_struct, vm_rb);
+                if (vma->vm_start < addr)
+                        continue;
+                if (vma->vm_start > addr)
+                        return NULL;
+                if (vma->vm_end == end) {
+                        mm->mmap_cache = vma;
+                        return vma;
+                }
+        }
+
+        return NULL;
 }
 
 /*
@@ -595,7 +792,7 @@ static int validate_mmap_request(struct file *file,
                                  unsigned long pgoff,
                                  unsigned long *_capabilities)
 {
-        unsigned long capabilities;
+        unsigned long capabilities, rlen;
         unsigned long reqprot = prot;
         int ret;
 
@@ -615,12 +812,12 @@ static int validate_mmap_request(struct file *file,
                 return -EINVAL;
 
         /* Careful about overflows.. */
-        len = PAGE_ALIGN(len);
-        if (!len || len > TASK_SIZE)
+        rlen = PAGE_ALIGN(len);
+        if (!rlen || rlen > TASK_SIZE)
                 return -ENOMEM;
 
         /* offset overflow? */
-        if ((pgoff + (len >> PAGE_SHIFT)) < pgoff)
+        if ((pgoff + (rlen >> PAGE_SHIFT)) < pgoff)
                 return -EOVERFLOW;
 
         if (file) {
@@ -794,9 +991,10 @@ static unsigned long determine_vm_flags(struct file *file,
 }
 
 /*
- * set up a shared mapping on a file
+ * set up a shared mapping on a file (the driver or filesystem provides and
+ * pins the storage)
  */
-static int do_mmap_shared_file(struct vm_area_struct *vma, unsigned long len)
+static int do_mmap_shared_file(struct vm_area_struct *vma)
 {
         int ret;
 
@@ -814,10 +1012,14 @@ static int do_mmap_shared_file(struct vm_area_struct *vma, unsigned long len)
 /*
  * set up a private mapping or an anonymous shared mapping
  */
-static int do_mmap_private(struct vm_area_struct *vma, unsigned long len)
+static int do_mmap_private(struct vm_area_struct *vma,
+                           struct vm_region *region,
+                           unsigned long len)
 {
+        struct page *pages;
+        unsigned long total, point, n, rlen;
         void *base;
-        int ret;
+        int ret, order;
 
         /* invoke the file's mapping function so that it can keep track of
          * shared mappings on devices or memory
@@ -836,23 +1038,46 @@ static int do_mmap_private(struct vm_area_struct *vma, unsigned long len)
                  * make a private copy of the data and map that instead */
         }
 
+        rlen = PAGE_ALIGN(len);
+
         /* allocate some memory to hold the mapping
          * - note that this may not return a page-aligned address if the object
          *   we're allocating is smaller than a page
          */
-        base = kmalloc(len, GFP_KERNEL|__GFP_COMP);
-        if (!base)
+        order = get_order(rlen);
+        kdebug("alloc order %d for %lx", order, len);
+
+        pages = alloc_pages(GFP_KERNEL, order);
+        if (!pages)
                 goto enomem;
 
-        vma->vm_start = (unsigned long) base;
-        vma->vm_end = vma->vm_start + len;
-        vma->vm_flags |= VM_MAPPED_COPY;
+        /* we allocated a power-of-2 sized page set, so we need to trim off the
+         * excess */
+        total = 1 << order;
+        atomic_add(total, &mmap_pages_allocated);
+
+        point = rlen >> PAGE_SHIFT;
+        while (total > point) {
+                order = ilog2(total - point);
+                n = 1 << order;
+                kdebug("shave %lu/%lu @%lu", n, total - point, total);
+                atomic_sub(n, &mmap_pages_allocated);
+                total -= n;
+                set_page_refcounted(pages + total);
+                __free_pages(pages + total, order);
+        }
+
+        total = rlen >> PAGE_SHIFT;
+        for (point = 1; point < total; point++)
+                set_page_refcounted(&pages[point]);
 
-#ifdef WARN_ON_SLACK
-        if (len + WARN_ON_SLACK <= kobjsize(result))
-                printk("Allocation of %lu bytes from process %d has %lu bytes of slack\n",
-                       len, current->pid, kobjsize(result) - len);
-#endif
+        base = page_address(pages);
+        region->vm_flags = vma->vm_flags |= VM_MAPPED_COPY;
+        region->vm_start = (unsigned long) base;
+        region->vm_end   = region->vm_start + rlen;
+
+        vma->vm_start = region->vm_start;
+        vma->vm_end   = region->vm_start + len;
 
         if (vma->vm_file) {
                 /* read the contents of a file into the copy */
@@ -864,26 +1089,27 @@ static int do_mmap_private(struct vm_area_struct *vma, unsigned long len)
 
                 old_fs = get_fs();
                 set_fs(KERNEL_DS);
-                ret = vma->vm_file->f_op->read(vma->vm_file, base, len, &fpos);
+                ret = vma->vm_file->f_op->read(vma->vm_file, base, rlen, &fpos);
                 set_fs(old_fs);
 
                 if (ret < 0)
                         goto error_free;
 
                 /* clear the last little bit */
-                if (ret < len)
-                        memset(base + ret, 0, len - ret);
+                if (ret < rlen)
+                        memset(base + ret, 0, rlen - ret);
 
         } else {
                 /* if it's an anonymous mapping, then just clear it */
-                memset(base, 0, len);
+                memset(base, 0, rlen);
         }
 
         return 0;
 
 error_free:
-        kfree(base);
-        vma->vm_start = 0;
+        free_page_series(region->vm_start, region->vm_end);
+        region->vm_start = vma->vm_start = 0;
+        region->vm_end   = vma->vm_end = 0;
         return ret;
 
 enomem:
@@ -903,13 +1129,14 @@ unsigned long do_mmap_pgoff(struct file *file,
                             unsigned long flags,
                             unsigned long pgoff)
 {
-        struct vm_list_struct *vml = NULL;
-        struct vm_area_struct *vma = NULL;
+        struct vm_area_struct *vma;
+        struct vm_region *region;
         struct rb_node *rb;
-        unsigned long capabilities, vm_flags;
-        void *result;
+        unsigned long capabilities, vm_flags, result;
         int ret;
 
+        kenter(",%lx,%lx,%lx,%lx,%lx", addr, len, prot, flags, pgoff);
+
         if (!(flags & MAP_FIXED))
                 addr = round_hint_to_min(addr);
 
@@ -917,73 +1144,120 @@ unsigned long do_mmap_pgoff(struct file *file,
          * mapping */
         ret = validate_mmap_request(file, addr, len, prot, flags, pgoff,
                                     &capabilities);
-        if (ret < 0)
+        if (ret < 0) {
+                kleave(" = %d [val]", ret);
                 return ret;
+        }
 
         /* we've determined that we can make the mapping, now translate what we
          * now know into VMA flags */
         vm_flags = determine_vm_flags(file, prot, flags, capabilities);
 
-        /* we're going to need to record the mapping if it works */
-        vml = kzalloc(sizeof(struct vm_list_struct), GFP_KERNEL);
-        if (!vml)
-                goto error_getting_vml;
+        /* we're going to need to record the mapping */
+        region = kmem_cache_zalloc(vm_region_jar, GFP_KERNEL);
+        if (!region)
+                goto error_getting_region;
+
+        vma = kmem_cache_zalloc(vm_area_cachep, GFP_KERNEL);
+        if (!vma)
+                goto error_getting_vma;
+
+        atomic_set(&region->vm_usage, 1);
+        region->vm_flags = vm_flags;
+        region->vm_pgoff = pgoff;
 
-        down_write(&nommu_vma_sem);
+        INIT_LIST_HEAD(&vma->anon_vma_node);
+        vma->vm_flags = vm_flags;
+        vma->vm_pgoff = pgoff;
 
-        /* if we want to share, we need to check for VMAs created by other
+        if (file) {
+                region->vm_file = file;
+                get_file(file);
+                vma->vm_file = file;
+                get_file(file);
+                if (vm_flags & VM_EXECUTABLE) {
+                        added_exe_file_vma(current->mm);
+                        vma->vm_mm = current->mm;
+                }
+        }
+
+        down_write(&nommu_region_sem);
+
+        /* if we want to share, we need to check for regions created by other
          * mmap() calls that overlap with our proposed mapping
-         * - we can only share with an exact match on most regular files
+         * - we can only share with a superset match on most regular files
          * - shared mappings on character devices and memory backed files are
          *   permitted to overlap inexactly as far as we are concerned for in
          *   these cases, sharing is handled in the driver or filesystem rather
          *   than here
          */
         if (vm_flags & VM_MAYSHARE) {
-                unsigned long pglen = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
-                unsigned long vmpglen;
+                struct vm_region *pregion;
+                unsigned long pglen, rpglen, pgend, rpgend, start;
 
-                /* suppress VMA sharing for shared regions */
-                if (vm_flags & VM_SHARED &&
-                    capabilities & BDI_CAP_MAP_DIRECT)
-                        goto dont_share_VMAs;
+                pglen = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
+                pgend = pgoff + pglen;
 
-                for (rb = rb_first(&nommu_vma_tree); rb; rb = rb_next(rb)) {
-                        vma = rb_entry(rb, struct vm_area_struct, vm_rb);
+                for (rb = rb_first(&nommu_region_tree); rb; rb = rb_next(rb)) {
+                        pregion = rb_entry(rb, struct vm_region, vm_rb);
 
-                        if (!(vma->vm_flags & VM_MAYSHARE))
+                        if (!(pregion->vm_flags & VM_MAYSHARE))
                                 continue;
 
                         /* search for overlapping mappings on the same file */
-                        if (vma->vm_file->f_path.dentry->d_inode != file->f_path.dentry->d_inode)
+                        if (pregion->vm_file->f_path.dentry->d_inode !=
+                            file->f_path.dentry->d_inode)
                                 continue;
 
-                        if (vma->vm_pgoff >= pgoff + pglen)
+                        if (pregion->vm_pgoff >= pgend)
                                 continue;
 
-                        vmpglen = vma->vm_end - vma->vm_start + PAGE_SIZE - 1;
-                        vmpglen >>= PAGE_SHIFT;
-                        if (pgoff >= vma->vm_pgoff + vmpglen)
+                        rpglen = pregion->vm_end - pregion->vm_start;
+                        rpglen = (rpglen + PAGE_SIZE - 1) >> PAGE_SHIFT;
+                        rpgend = pregion->vm_pgoff + rpglen;
+                        if (pgoff >= rpgend)
                                 continue;
 
-                        /* handle inexactly overlapping matches between mappings */
-                        if (vma->vm_pgoff != pgoff || vmpglen != pglen) {
+                        /* handle inexactly overlapping matches between
+                         * mappings */
+                        if ((pregion->vm_pgoff != pgoff || rpglen != pglen) &&
+                            !(pgoff >= pregion->vm_pgoff && pgend <= rpgend)) {
+                                /* new mapping is not a subset of the region */
                                 if (!(capabilities & BDI_CAP_MAP_DIRECT))
                                         goto sharing_violation;
                                 continue;
                         }
 
-                        /* we've found a VMA we can share */
-                        atomic_inc(&vma->vm_usage);
-
-                        vml->vma = vma;
-                        result = (void *) vma->vm_start;
-                        goto shared;
+                        /* we've found a region we can share */
+                        atomic_inc(&pregion->vm_usage);
+                        vma->vm_region = pregion;
+                        start = pregion->vm_start;
+                        start += (pgoff - pregion->vm_pgoff) << PAGE_SHIFT;
+                        vma->vm_start = start;
+                        vma->vm_end = start + len;
+
+                        if (pregion->vm_flags & VM_MAPPED_COPY) {
+                                kdebug("share copy");
+                                vma->vm_flags |= VM_MAPPED_COPY;
+                        } else {
+                                kdebug("share mmap");
+                                ret = do_mmap_shared_file(vma);
+                                if (ret < 0) {
+                                        vma->vm_region = NULL;
+                                        vma->vm_start = 0;
+                                        vma->vm_end = 0;
+                                        atomic_dec(&pregion->vm_usage);
+                                        pregion = NULL;
+                                        goto error_just_free;
+                                }
+                        }
+                        fput(region->vm_file);
+                        kmem_cache_free(vm_region_jar, region);
+                        region = pregion;
+                        result = start;
+                        goto share;
                 }
 
-        dont_share_VMAs:
-                vma = NULL;
-
                 /* obtain the address at which to make a shared mapping
                  * - this is the hook for quasi-memory character devices to
                  *   tell us the location of a shared mapping
@@ -994,102 +1268,93 @@ unsigned long do_mmap_pgoff(struct file *file,
                         if (IS_ERR((void *) addr)) {
                                 ret = addr;
                                 if (ret != (unsigned long) -ENOSYS)
-                                        goto error;
+                                        goto error_just_free;
 
                                 /* the driver refused to tell us where to site
                                  * the mapping so we'll have to attempt to copy
                                  * it */
                                 ret = (unsigned long) -ENODEV;
                                 if (!(capabilities & BDI_CAP_MAP_COPY))
-                                        goto error;
+                                        goto error_just_free;
 
                                 capabilities &= ~BDI_CAP_MAP_DIRECT;
+                        } else {
+                                vma->vm_start = region->vm_start = addr;
+                                vma->vm_end = region->vm_end = addr + len;
                         }
                 }
         }
 
-        /* we're going to need a VMA struct as well */
-        vma = kzalloc(sizeof(struct vm_area_struct), GFP_KERNEL);
-        if (!vma)
-                goto error_getting_vma;
-
-        INIT_LIST_HEAD(&vma->anon_vma_node);
-        atomic_set(&vma->vm_usage, 1);
-        if (file) {
-                get_file(file);
-                if (vm_flags & VM_EXECUTABLE) {
-                        added_exe_file_vma(current->mm);
-                        vma->vm_mm = current->mm;
-                }
-        }
-        vma->vm_file    = file;
-        vma->vm_flags   = vm_flags;
-        vma->vm_start   = addr;
-        vma->vm_end     = addr + len;
-        vma->vm_pgoff   = pgoff;
-
-        vml->vma = vma;
+        vma->vm_region = region;
 
         /* set up the mapping */
         if (file && vma->vm_flags & VM_SHARED)
-                ret = do_mmap_shared_file(vma, len);
+                ret = do_mmap_shared_file(vma);
         else
-                ret = do_mmap_private(vma, len);
+                ret = do_mmap_private(vma, region, len);
         if (ret < 0)
-                goto error;
+                goto error_put_region;
+
+        add_nommu_region(region);
 
         /* okay... we have a mapping; now we have to register it */
-        result = (void *) vma->vm_start;
+        result = vma->vm_start;
 
         current->mm->total_vm += len >> PAGE_SHIFT;
 
-        add_nommu_vma(vma);
+share:
+        add_vma_to_mm(current->mm, vma);
 
- shared:
-        add_vma_to_mm(current->mm, vml);
-
-        up_write(&nommu_vma_sem);
+        up_write(&nommu_region_sem);
 
         if (prot & PROT_EXEC)
-                flush_icache_range((unsigned long) result,
-                                   (unsigned long) result + len);
+                flush_icache_range(result, result + len);
 
-#ifdef DEBUG
-        printk("do_mmap:\n");
-        show_process_blocks();
-#endif
+        kleave(" = %lx", result);
+        return result;
 
-        return (unsigned long) result;
-
- error:
-        up_write(&nommu_vma_sem);
-        kfree(vml);
+error_put_region:
+        __put_nommu_region(region);
         if (vma) {
                 if (vma->vm_file) {
                         fput(vma->vm_file);
                         if (vma->vm_flags & VM_EXECUTABLE)
                                 removed_exe_file_vma(vma->vm_mm);
                 }
-                kfree(vma);
+                kmem_cache_free(vm_area_cachep, vma);
         }
+        kleave(" = %d [pr]", ret);
         return ret;
 
- sharing_violation:
-        up_write(&nommu_vma_sem);
-        printk("Attempt to share mismatched mappings\n");
-        kfree(vml);
-        return -EINVAL;
+error_just_free:
+        up_write(&nommu_region_sem);
+error:
+        fput(region->vm_file);
+        kmem_cache_free(vm_region_jar, region);
+        fput(vma->vm_file);
+        if (vma->vm_flags & VM_EXECUTABLE)
+                removed_exe_file_vma(vma->vm_mm);
+        kmem_cache_free(vm_area_cachep, vma);
+        kleave(" = %d", ret);
+        return ret;
+
+sharing_violation:
+        up_write(&nommu_region_sem);
+        printk(KERN_WARNING "Attempt to share mismatched mappings\n");
+        ret = -EINVAL;
+        goto error;
 
- error_getting_vma:
-        up_write(&nommu_vma_sem);
-        kfree(vml);
-        printk("Allocation of vma for %lu byte allocation from process %d failed\n",
+error_getting_vma:
+        kmem_cache_free(vm_region_jar, region);
+        printk(KERN_WARNING "Allocation of vma for %lu byte allocation"
+               " from process %d failed\n",
                len, current->pid);
         show_free_areas();
         return -ENOMEM;
 
- error_getting_vml:
-        printk("Allocation of vml for %lu byte allocation from process %d failed\n",
+error_getting_region:
+        printk(KERN_WARNING "Allocation of vm region for %lu byte allocation"
+               " from process %d failed\n",
                len, current->pid);
         show_free_areas();
         return -ENOMEM;
@@ -1097,77 +1362,180 @@ unsigned long do_mmap_pgoff(struct file *file,
 EXPORT_SYMBOL(do_mmap_pgoff);
 
 /*
- * handle mapping disposal for uClinux
+ * split a vma into two pieces at address 'addr', a new vma is allocated either
+ * for the first part or the tail.
  */
-static void put_vma(struct mm_struct *mm, struct vm_area_struct *vma)
+int split_vma(struct mm_struct *mm, struct vm_area_struct *vma,
+              unsigned long addr, int new_below)
 {
-        if (vma) {
-                down_write(&nommu_vma_sem);
+        struct vm_area_struct *new;
+        struct vm_region *region;
+        unsigned long npages;
 
-                if (atomic_dec_and_test(&vma->vm_usage)) {
-                        delete_nommu_vma(vma);
+        kenter("");
 
-                        if (vma->vm_ops && vma->vm_ops->close)
-                                vma->vm_ops->close(vma);
+        /* we're only permitted to split anonymous regions that have a single
+         * owner */
+        if (vma->vm_file ||
+            atomic_read(&vma->vm_region->vm_usage) != 1)
+                return -ENOMEM;
 
-                        /* IO memory and memory shared directly out of the pagecache from
-                         * ramfs/tmpfs mustn't be released here */
-                        if (vma->vm_flags & VM_MAPPED_COPY)
-                                kfree((void *) vma->vm_start);
+        if (mm->map_count >= sysctl_max_map_count)
+                return -ENOMEM;
 
-                        if (vma->vm_file) {
-                                fput(vma->vm_file);
-                                if (vma->vm_flags & VM_EXECUTABLE)
-                                        removed_exe_file_vma(mm);
-                        }
-                        kfree(vma);
-                }
+        region = kmem_cache_alloc(vm_region_jar, GFP_KERNEL);
+        if (!region)
+                return -ENOMEM;
+
+        new = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
+        if (!new) {
+                kmem_cache_free(vm_region_jar, region);
+                return -ENOMEM;
+        }
+
+        /* most fields are the same, copy all, and then fixup */
+        *new = *vma;
+        *region = *vma->vm_region;
+        new->vm_region = region;
+
+        npages = (addr - vma->vm_start) >> PAGE_SHIFT;
+
+        if (new_below) {
+                region->vm_end = new->vm_end = addr;
+        } else {
+                region->vm_start = new->vm_start = addr;
+                region->vm_pgoff = new->vm_pgoff += npages;
+        }
 
-                up_write(&nommu_vma_sem);
+        if (new->vm_ops && new->vm_ops->open)
+                new->vm_ops->open(new);
+
+        delete_vma_from_mm(vma);
+        down_write(&nommu_region_sem);
+        delete_nommu_region(vma->vm_region);
+        if (new_below) {
+                vma->vm_region->vm_start = vma->vm_start = addr;
+                vma->vm_region->vm_pgoff = vma->vm_pgoff += npages;
+        } else {
+                vma->vm_region->vm_end = vma->vm_end = addr;
         }
+        add_nommu_region(vma->vm_region);
+        add_nommu_region(new->vm_region);
+        up_write(&nommu_region_sem);
+        add_vma_to_mm(mm, vma);
+        add_vma_to_mm(mm, new);
+        return 0;
 }
 
 /*
- * release a mapping
- * - under NOMMU conditions the parameters must match exactly to the mapping to
- *   be removed
+ * shrink a VMA by removing the specified chunk from either the beginning or
+ * the end
  */
-int do_munmap(struct mm_struct *mm, unsigned long addr, size_t len)
+static int shrink_vma(struct mm_struct *mm,
+                      struct vm_area_struct *vma,
+                      unsigned long from, unsigned long to)
 {
-        struct vm_list_struct *vml, **parent;
-        unsigned long end = addr + len;
+        struct vm_region *region;
 
-#ifdef DEBUG
-        printk("do_munmap:\n");
-#endif
+        kenter("");
 
-        for (parent = &mm->context.vmlist; *parent; parent = &(*parent)->next) {
-                if ((*parent)->vma->vm_start > addr)
-                        break;
-                if ((*parent)->vma->vm_start == addr &&
-                    ((len == 0) || ((*parent)->vma->vm_end == end)))
-                        goto found;
-        }
+        /* adjust the VMA's pointers, which may reposition it in the MM's tree
+         * and list */
+        delete_vma_from_mm(vma);
+        if (from > vma->vm_start)
+                vma->vm_end = from;
+        else
+                vma->vm_start = to;
+        add_vma_to_mm(mm, vma);
 
-        printk("munmap of non-mmaped memory by process %d (%s): %p\n",
-               current->pid, current->comm, (void *) addr);
-        return -EINVAL;
+        /* cut the backing region down to size */
+        region = vma->vm_region;
+        BUG_ON(atomic_read(&region->vm_usage) != 1);
 
- found:
-        vml = *parent;
+        down_write(&nommu_region_sem);
+        delete_nommu_region(region);
+        if (from > region->vm_start)
+                region->vm_end = from;
+        else
+                region->vm_start = to;
+        add_nommu_region(region);
+        up_write(&nommu_region_sem);
 
-        put_vma(mm, vml->vma);
+        free_page_series(from, to);
+        return 0;
+}
 
-        *parent = vml->next;
-        kfree(vml);
+/*
+ * release a mapping
+ * - under NOMMU conditions the chunk to be unmapped must be backed by a single
+ *   VMA, though it need not cover the whole VMA
+ */
+int do_munmap(struct mm_struct *mm, unsigned long start, size_t len)
+{
+        struct vm_area_struct *vma;
+        struct rb_node *rb;
+        unsigned long end = start + len;
+        int ret;
 
-        update_hiwater_vm(mm);
-        mm->total_vm -= len >> PAGE_SHIFT;
+        kenter(",%lx,%zx", start, len);
 
-#ifdef DEBUG
-        show_process_blocks();
-#endif
+        if (len == 0)
+                return -EINVAL;
+
+        /* find the first potentially overlapping VMA */
+        vma = find_vma(mm, start);
+        if (!vma) {
+                printk(KERN_WARNING
+                       "munmap of memory not mmapped by process %d (%s):"
+                       " 0x%lx-0x%lx\n",
+                       current->pid, current->comm, start, start + len - 1);
+                return -EINVAL;
+        }
 
+        /* we're allowed to split an anonymous VMA but not a file-backed one */
+        if (vma->vm_file) {
+                do {
+                        if (start > vma->vm_start) {
+                                kleave(" = -EINVAL [miss]");
+                                return -EINVAL;
+                        }
+                        if (end == vma->vm_end)
+                                goto erase_whole_vma;
+                        rb = rb_next(&vma->vm_rb);
+                        vma = rb_entry(rb, struct vm_area_struct, vm_rb);
+                } while (rb);
+                kleave(" = -EINVAL [split file]");
+                return -EINVAL;
+        } else {
+                /* the chunk must be a subset of the VMA found */
+                if (start == vma->vm_start && end == vma->vm_end)
+                        goto erase_whole_vma;
+                if (start < vma->vm_start || end > vma->vm_end) {
+                        kleave(" = -EINVAL [superset]");
+                        return -EINVAL;
+                }
+                if (start & ~PAGE_MASK) {
+                        kleave(" = -EINVAL [unaligned start]");
+                        return -EINVAL;
+                }
+                if (end != vma->vm_end && end & ~PAGE_MASK) {
+                        kleave(" = -EINVAL [unaligned split]");
+                        return -EINVAL;
+                }
+                if (start != vma->vm_start && end != vma->vm_end) {
+                        ret = split_vma(mm, vma, start, 1);
+                        if (ret < 0) {
+                                kleave(" = %d [split]", ret);
+                                return ret;
+                        }
+                }
+                return shrink_vma(mm, vma, start, end);
+        }
+
+erase_whole_vma:
+        delete_vma_from_mm(vma);
+        delete_vma(mm, vma);
+        kleave(" = 0");
         return 0;
 }
 EXPORT_SYMBOL(do_munmap);
@@ -1184,29 +1552,26 @@ asmlinkage long sys_munmap(unsigned long addr, size_t len)
 }
 
 /*
- * Release all mappings
+ * release all the mappings made in a process's VM space
  */
-void exit_mmap(struct mm_struct * mm)
+void exit_mmap(struct mm_struct *mm)
 {
-        struct vm_list_struct *tmp;
+        struct vm_area_struct *vma;
 
-        if (mm) {
-#ifdef DEBUG
-                printk("Exit_mmap:\n");
-#endif
+        if (!mm)
+                return;
 
-                mm->total_vm = 0;
+        kenter("");
 
-                while ((tmp = mm->context.vmlist)) {
-                        mm->context.vmlist = tmp->next;
-                        put_vma(mm, tmp->vma);
-                        kfree(tmp);
-                }
+        mm->total_vm = 0;
 
-#ifdef DEBUG
-                show_process_blocks();
-#endif
+        while ((vma = mm->mmap)) {
+                mm->mmap = vma->vm_next;
+                delete_vma_from_mm(vma);
+                delete_vma(mm, vma);
         }
+
+        kleave("");
 }
 
 unsigned long do_brk(unsigned long addr, unsigned long len)
@@ -1219,8 +1584,8 @@ unsigned long do_brk(unsigned long addr, unsigned long len)
  * time (controlled by the MREMAP_MAYMOVE flag and available VM space)
  *
  * under NOMMU conditions, we only permit changing a mapping's size, and only
- * as long as it stays within the hole allocated by the kmalloc() call in
- * do_mmap_pgoff() and the block is not shareable
+ * as long as it stays within the region allocated by do_mmap_private() and the
+ * block is not shareable
  *
  * MREMAP_FIXED is not supported under NOMMU conditions
  */
@@ -1231,13 +1596,16 @@ unsigned long do_mremap(unsigned long addr,
         struct vm_area_struct *vma;
 
         /* insanity checks first */
-        if (new_len == 0)
+        if (old_len == 0 || new_len == 0)
                 return (unsigned long) -EINVAL;
 
+        if (addr & ~PAGE_MASK)
+                return -EINVAL;
+
         if (flags & MREMAP_FIXED && new_addr != addr)
                 return (unsigned long) -EINVAL;
 
-        vma = find_vma_exact(current->mm, addr);
+        vma = find_vma_exact(current->mm, addr, old_len);
         if (!vma)
                 return (unsigned long) -EINVAL;
 
@@ -1247,19 +1615,19 @@ unsigned long do_mremap(unsigned long addr,
         if (vma->vm_flags & VM_MAYSHARE)
                 return (unsigned long) -EPERM;
 
-        if (new_len > kobjsize((void *) addr))
+        if (new_len > vma->vm_region->vm_end - vma->vm_region->vm_start)
                 return (unsigned long) -ENOMEM;
 
         /* all checks complete - do it */
         vma->vm_end = vma->vm_start + new_len;
-
         return vma->vm_start;
 }
 EXPORT_SYMBOL(do_mremap);
 
-asmlinkage unsigned long sys_mremap(unsigned long addr,
-        unsigned long old_len, unsigned long new_len,
-        unsigned long flags, unsigned long new_addr)
+asmlinkage
+unsigned long sys_mremap(unsigned long addr,
+                         unsigned long old_len, unsigned long new_len,
+                         unsigned long flags, unsigned long new_addr)
 {
         unsigned long ret;