staging: zsmalloc: remove x86 dependency

This patch replaces the page table assisted object mapping
method, which has x86 dependencies, with a arch-independent
method that does a simple copy into a temporary per-cpu
buffer.

While a copy seems like it would be worse than mapping the pages,
tests demonstrate the copying is always faster and, in the case of
running inside a KVM guest, roughly 4x faster.

Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

3 files changed, 72 insertions, 36 deletions

diff --git a/drivers/staging/zsmalloc/Kconfig b/drivers/staging/zsmalloc/Kconfig
index a5ab7200626..90845656579 100644
--- a/drivers/staging/zsmalloc/Kconfig
+++ b/drivers/staging/zsmalloc/Kconfig
@@ -1,9 +1,5 @@
 config ZSMALLOC
         tristate "Memory allocator for compressed pages"
-        # X86 dependency is because of the use of __flush_tlb_one and set_pte
-        # in zsmalloc-main.c.
-        # TODO: convert these to portable functions
-        depends on X86
         default n
         help
           zsmalloc is a slab-based memory allocator designed to store
diff --git a/drivers/staging/zsmalloc/zsmalloc-main.c b/drivers/staging/zsmalloc/zsmalloc-main.c
index 10b0d600026..a7a6f225bbf 100644
--- a/drivers/staging/zsmalloc/zsmalloc-main.c
+++ b/drivers/staging/zsmalloc/zsmalloc-main.c
@@ -470,6 +470,57 @@ static struct page *find_get_zspage(struct size_class *class)
         return page;
 }
 
+static void zs_copy_map_object(char *buf, struct page *firstpage,
+                                int off, int size)
+{
+        struct page *pages[2];
+        int sizes[2];
+        void *addr;
+
+        pages[0] = firstpage;
+        pages[1] = get_next_page(firstpage);
+        BUG_ON(!pages[1]);
+
+        sizes[0] = PAGE_SIZE - off;
+        sizes[1] = size - sizes[0];
+
+        /* disable page faults to match kmap_atomic() return conditions */
+        pagefault_disable();
+
+        /* copy object to per-cpu buffer */
+        addr = kmap_atomic(pages[0]);
+        memcpy(buf, addr + off, sizes[0]);
+        kunmap_atomic(addr);
+        addr = kmap_atomic(pages[1]);
+        memcpy(buf + sizes[0], addr, sizes[1]);
+        kunmap_atomic(addr);
+}
+
+static void zs_copy_unmap_object(char *buf, struct page *firstpage,
+                                int off, int size)
+{
+        struct page *pages[2];
+        int sizes[2];
+        void *addr;
+
+        pages[0] = firstpage;
+        pages[1] = get_next_page(firstpage);
+        BUG_ON(!pages[1]);
+
+        sizes[0] = PAGE_SIZE - off;
+        sizes[1] = size - sizes[0];
+
+        /* copy per-cpu buffer to object */
+        addr = kmap_atomic(pages[0]);
+        memcpy(addr + off, buf, sizes[0]);
+        kunmap_atomic(addr);
+        addr = kmap_atomic(pages[1]);
+        memcpy(addr, buf + sizes[0], sizes[1]);
+        kunmap_atomic(addr);
+
+        /* enable page faults to match kunmap_atomic() return conditions */
+        pagefault_enable();
+}
 
 static int zs_cpu_notifier(struct notifier_block *nb, unsigned long action,
                                 void *pcpu)
@@ -480,18 +531,23 @@ static int zs_cpu_notifier(struct notifier_block *nb, unsigned long action,
         switch (action) {
         case CPU_UP_PREPARE:
                 area = &per_cpu(zs_map_area, cpu);
-                if (area->vm)
-                        break;
-                area->vm = alloc_vm_area(2 * PAGE_SIZE, area->vm_ptes);
-                if (!area->vm)
-                        return notifier_from_errno(-ENOMEM);
+                /*
+                 * Make sure we don't leak memory if a cpu UP notification
+                 * and zs_init() race and both call zs_cpu_up() on the same cpu
+                 */
+                if (area->vm_buf)
+                        return 0;
+                area->vm_buf = (char *)__get_free_page(GFP_KERNEL);
+                if (!area->vm_buf)
+                        return -ENOMEM;
+                return 0;
                 break;
         case CPU_DEAD:
         case CPU_UP_CANCELED:
                 area = &per_cpu(zs_map_area, cpu);
-                if (area->vm)
-                        free_vm_area(area->vm);
-                area->vm = NULL;
+                if (area->vm_buf)
+                        free_page((unsigned long)area->vm_buf);
+                area->vm_buf = NULL;
                 break;
         }
 
@@ -714,22 +770,11 @@ void *zs_map_object(struct zs_pool *pool, unsigned long handle)
         if (off + class->size <= PAGE_SIZE) {
                 /* this object is contained entirely within a page */
                 area->vm_addr = kmap_atomic(page);
-        } else {
-                /* this object spans two pages */
-                struct page *nextp;
-
-                nextp = get_next_page(page);
-                BUG_ON(!nextp);
-
-
-                set_pte(area->vm_ptes[0], mk_pte(page, PAGE_KERNEL));
-                set_pte(area->vm_ptes[1], mk_pte(nextp, PAGE_KERNEL));
-
-                /* We pre-allocated VM area so mapping can never fail */
-                area->vm_addr = area->vm->addr;
+                return area->vm_addr + off;
         }
 
-        return area->vm_addr + off;
+        zs_copy_map_object(area->vm_buf, page, off, class->size);
+        return area->vm_buf;
 }
 EXPORT_SYMBOL_GPL(zs_map_object);
 
@@ -751,14 +796,10 @@ void zs_unmap_object(struct zs_pool *pool, unsigned long handle)
         off = obj_idx_to_offset(page, obj_idx, class->size);
 
         area = &__get_cpu_var(zs_map_area);
-        if (off + class->size <= PAGE_SIZE) {
+        if (off + class->size <= PAGE_SIZE)
                 kunmap_atomic(area->vm_addr);
-        } else {
-                set_pte(area->vm_ptes[0], __pte(0));
-                set_pte(area->vm_ptes[1], __pte(0));
-                __flush_tlb_one((unsigned long)area->vm_addr);
-                __flush_tlb_one((unsigned long)area->vm_addr + PAGE_SIZE);
-        }
+        else
+                zs_copy_unmap_object(area->vm_buf, page, off, class->size);
         put_cpu_var(zs_map_area);
 }
 EXPORT_SYMBOL_GPL(zs_unmap_object);
diff --git a/drivers/staging/zsmalloc/zsmalloc_int.h b/drivers/staging/zsmalloc/zsmalloc_int.h
index 6fd32a9e031..f760dae54f2 100644
--- a/drivers/staging/zsmalloc/zsmalloc_int.h
+++ b/drivers/staging/zsmalloc/zsmalloc_int.h
@@ -110,9 +110,8 @@ enum fullness_group {
 static const int fullness_threshold_frac = 4;
 
 struct mapping_area {
-        struct vm_struct *vm;
-        pte_t *vm_ptes[2];
-        char *vm_addr;
+        char *vm_buf; /* copy buffer for objects that span pages */
+        char *vm_addr; /* address of kmap_atomic()'ed pages */
 };
 
 struct size_class {