[PATCH] unpaged: VM_UNPAGED

Although we tend to associate VM_RESERVED with remap_pfn_range, quite a few
drivers set VM_RESERVED on areas which are then populated by nopage.  The
PageReserved removal in 2.6.15-rc1 changed VM_RESERVED not to free pages in
zap_pte_range, without changing those drivers not to set it: so their pages
just leak away.

Let's not change miscellaneous drivers now: introduce VM_UNPAGED at the core,
to flag the special areas where the ptes may have no struct page, or if they
have then it's not to be touched.  Replace most instances of VM_RESERVED in
core mm by VM_UNPAGED.  Force it on in remap_pfn_range, and the sparc and
sparc64 io_remap_pfn_range.

Revert addition of VM_RESERVED to powerpc vdso, it's not needed there.  Is it
needed anywhere?  It still governs the mm->reserved_vm statistic, and special
vmas not to be merged, and areas not to be core dumped; but could probably be
eliminated later (the drivers are probably specifying it because in 2.4 it
kept swapout off the vma, but in 2.6 we work from the LRU, which these pages
don't get on).

Use the VM_SHM slot for VM_UNPAGED, and define VM_SHM to 0: it serves no
purpose whatsoever, and should be removed from drivers when we clean up.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Acked-by: William Irwin <wli@holomorphy.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 18 insertions, 12 deletions

diff --git a/mm/memory.c b/mm/memory.c
index cfce5f1f30f2..ece04963158e 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -334,7 +334,7 @@ static inline void add_mm_rss(struct mm_struct *mm, int file_rss, int anon_rss)
 
 /*
  * This function is called to print an error when a pte in a
- * !VM_RESERVED region is found pointing to an invalid pfn (which
+ * !VM_UNPAGED region is found pointing to an invalid pfn (which
  * is an error.
  *
  * The calling function must still handle the error.
@@ -381,15 +381,15 @@ copy_one_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
                 goto out_set_pte;
         }
 
-        /* If the region is VM_RESERVED, the mapping is not
+        /* If the region is VM_UNPAGED, the mapping is not
          * mapped via rmap - duplicate the pte as is.
          */
-        if (vm_flags & VM_RESERVED)
+        if (vm_flags & VM_UNPAGED)
                 goto out_set_pte;
 
         pfn = pte_pfn(pte);
         /* If the pte points outside of valid memory but
-         * the region is not VM_RESERVED, we have a problem.
+         * the region is not VM_UNPAGED, we have a problem.
          */
         if (unlikely(!pfn_valid(pfn))) {
                 print_bad_pte(vma, pte, addr);
@@ -528,7 +528,7 @@ int copy_page_range(struct mm_struct *dst_mm, struct mm_struct *src_mm,
          * readonly mappings. The tradeoff is that copy_page_range is more
          * efficient than faulting.
          */
-        if (!(vma->vm_flags & (VM_HUGETLB|VM_NONLINEAR|VM_RESERVED))) {
+        if (!(vma->vm_flags & (VM_HUGETLB|VM_NONLINEAR|VM_UNPAGED))) {
                 if (!vma->anon_vma)
                         return 0;
         }
@@ -572,7 +572,7 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
 
                         (*zap_work) -= PAGE_SIZE;
 
-                        if (!(vma->vm_flags & VM_RESERVED)) {
+                        if (!(vma->vm_flags & VM_UNPAGED)) {
                                 unsigned long pfn = pte_pfn(ptent);
                                 if (unlikely(!pfn_valid(pfn)))
                                         print_bad_pte(vma, ptent, addr);
@@ -1191,10 +1191,16 @@ int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr,
          * rest of the world about it:
          *   VM_IO tells people not to look at these pages
          *      (accesses can have side effects).
-         *   VM_RESERVED tells the core MM not to "manage" these pages
-         *      (e.g. refcount, mapcount, try to swap them out).
+         *   VM_RESERVED is specified all over the place, because
+         *      in 2.4 it kept swapout's vma scan off this vma; but
+         *      in 2.6 the LRU scan won't even find its pages, so this
+         *      flag means no more than count its pages in reserved_vm,
+         *      and omit it from core dump, even when VM_IO turned off.
+         *   VM_UNPAGED tells the core MM not to "manage" these pages
+         *      (e.g. refcount, mapcount, try to swap them out): in
+         *      particular, zap_pte_range does not try to free them.
          */
-        vma->vm_flags |= VM_IO | VM_RESERVED;
+        vma->vm_flags |= VM_IO | VM_RESERVED | VM_UNPAGED;
 
         BUG_ON(addr >= end);
         pfn -= addr >> PAGE_SHIFT;
@@ -1276,7 +1282,7 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
         pte_t entry;
         int ret = VM_FAULT_MINOR;
 
-        BUG_ON(vma->vm_flags & VM_RESERVED);
+        BUG_ON(vma->vm_flags & VM_UNPAGED);
 
         if (unlikely(!pfn_valid(pfn))) {
                 /*
@@ -1924,7 +1930,7 @@ retry:
                         inc_mm_counter(mm, anon_rss);
                         lru_cache_add_active(new_page);
                         page_add_anon_rmap(new_page, vma, address);
-                } else if (!(vma->vm_flags & VM_RESERVED)) {
+                } else if (!(vma->vm_flags & VM_UNPAGED)) {
                         inc_mm_counter(mm, file_rss);
                         page_add_file_rmap(new_page);
                 }
@@ -2203,7 +2209,7 @@ static int __init gate_vma_init(void)
         gate_vma.vm_start = FIXADDR_USER_START;
         gate_vma.vm_end = FIXADDR_USER_END;
         gate_vma.vm_page_prot = PAGE_READONLY;
-        gate_vma.vm_flags = VM_RESERVED;
+        gate_vma.vm_flags = 0;
         return 0;
 }
 __initcall(gate_vma_init);