[Xen-devel] [PATCH 3/3] xencomm take 4: linux side remove xencomm page size limit

[Isaku Yamahata <yamahata@xxxxxxxxxxxxx>]

# HG changeset patch
# User yamahata@xxxxxxxxxxxxx
# Date 1187582891 -32400
# Node ID 603694f91c98a6a4f12dcd729053f9ba38d5fc11
# Parent  b5fdf02c38f4765697196f5fad5d1262f2c157f4
remove xencomm page size limit.
Currently xencomm has page size limit so that a domain with many memory
(e.g. 100GB~) can't be created.

Now that xencomm of xen side accepts struct xencomm_desc whose address array
crosses page boundary. Thus it isn't necessary to allocate single page
not to cross page boundary. We can allocate exact sized memory.
Note that struct xencomm_desc can't cross page boundary and slab allocator
returns sizeof(void*) aligned pointer.
Where sizeof(*desc) > sizeof(void*), e.g. 32 bit environment,
the slab allocator return pointer doesn't gurantee that
struct xencomm_desc doesn't cross page boundary. So we fall back to
page allocator.
PATCHNAME: remove_xencomm_page_size_limit_common_code

Signed-off-by: Isaku Yamahata <yamahata@xxxxxxxxxxxxx>

diff -r b5fdf02c38f4 -r 603694f91c98 drivers/xen/core/xencomm.c
--- a/drivers/xen/core/xencomm.c        Thu Aug 16 13:44:51 2007 -0600
+++ b/drivers/xen/core/xencomm.c        Mon Aug 20 13:08:11 2007 +0900
@@ -68,25 +68,54 @@ static int xencomm_init(struct xencomm_d
        return 0;
 }
 
-/* XXX use slab allocator */
-static struct xencomm_desc *xencomm_alloc(gfp_t gfp_mask)
-{
-       struct xencomm_desc *desc;
-
-       desc = (struct xencomm_desc *)__get_free_page(gfp_mask);
-       if (desc == NULL)
-               return NULL;
-
-       desc->nr_addrs = (PAGE_SIZE - sizeof(struct xencomm_desc)) /
+static struct xencomm_desc *xencomm_alloc(gfp_t gfp_mask,
+                                         void *buffer, unsigned long bytes)
+{
+       struct xencomm_desc *desc;
+       unsigned long buffer_ulong = (unsigned long)buffer;
+       unsigned long start = buffer_ulong & PAGE_MASK;
+       unsigned long end = (buffer_ulong + bytes) | ~PAGE_MASK;
+       unsigned long nr_addrs = (end - start + 1) >> PAGE_SHIFT;
+       unsigned long size = sizeof(*desc) +
+               sizeof(desc->address[0]) * nr_addrs;
+
+       /*
+        * slab allocator returns at least sizeof(void*) aligned pointer.
+        * When sizeof(*desc) > sizeof(void*), struct xencomm_desc might
+        * cross page boundary.
+        */
+       if (sizeof(*desc) > sizeof(void*)) {
+               unsigned long order = get_order(size);
+               desc = (struct xencomm_desc *)__get_free_pages(gfp_mask,
+                                                              order);
+               if (desc == NULL)
+                       return NULL;
+
+               desc->nr_addrs =
+                       ((PAGE_SIZE << order) - sizeof(struct xencomm_desc)) /
                        sizeof(*desc->address);
-
+       } else {
+               desc = kmalloc(size, gfp_mask);
+               if (desc == NULL)
+                       return NULL;
+
+               desc->nr_addrs = nr_addrs;
+       }
        return desc;
 }
 
 void xencomm_free(struct xencomm_handle *desc)
 {
-       if (desc && !((ulong)desc & XENCOMM_INLINE_FLAG))
-               free_page((unsigned long)__va(desc));
+       if (desc && !((ulong)desc & XENCOMM_INLINE_FLAG)) {
+               struct xencomm_desc *desc__ = (struct xencomm_desc*)desc;
+               if (sizeof(*desc__) > sizeof(void*)) {
+                       unsigned long size = sizeof(*desc__) +
+                               sizeof(desc__->address[0]) * desc__->nr_addrs;
+                       unsigned long order = get_order(size);
+                       free_pages((unsigned long)__va(desc), order);
+               } else
+                       kfree(__va(desc));
+       }
 }
 
 static int xencomm_create(void *buffer, unsigned long bytes, struct 
xencomm_desc **ret, gfp_t gfp_mask)
@@ -105,7 +134,7 @@ static int xencomm_create(void *buffer, 
 
        BUG_ON(buffer == NULL); /* 'bytes' is non-zero */
 
-       desc = xencomm_alloc(gfp_mask);
+       desc = xencomm_alloc(gfp_mask, buffer, bytes);
        if (!desc) {
                printk("%s failure\n", "xencomm_alloc");
                return -ENOMEM;

Attachment: 188_603694f91c98_remove_xencomm_page_size_limit_common_code.patch
Description: Text Data

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