First step, allocating a memory fragment with size 1KB bytes uses
page_frag_alloc_align. It will allocate PAGE_FRAG_CACHE_MAX_SIZE
bytes by __page_frag_cache_refill, store the pointer at nc->va and
then return the last 1KB memory fragment which address is nc->va
+ PAGE_FRAG_CACHE_MAX_SIZE - 1KB. The remaining PAGE_FRAG_CACHE_MAX_SIZE
- 1KB bytes of memory can Meet future memory requests.
Second step, if the caller requests a memory fragment with size
more then PAGE_FRAG_CACHE_MAX_SIZE bytes, page_frag_alloc_align,
it will also allocate PAGE_FRAG_CACHE_MAX_SIZE bytes by
__page_frag_cache_refill, store the pointer at nc->va, and
return NULL. this behavior makes the rest of
PAGE_FRAG_CACHE_MAX_SIZE - 1KB bytes memory at First step are
wasted(allocate from buddy system but not used).
So we should check the size of memory requests. If it beyound
PAGE_FRAG_CACHE_MAX_SIZE, we should return NULL directly.
Signed-off-by: wang wei <a929244872@xxxxxxx>
---
mm/page_alloc.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 8cf86d0c6aa8..3182c648e86e 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4757,6 +4757,9 @@ void *page_frag_alloc_align(struct page_frag_cache *nc,
struct page *page;
int offset;
+ if（unlikely(fragsz > PAGE_FRAG_CACHE_MAX_SIZE)）
+ return NULL;
+
if (unlikely(!nc->va)) {
refill:
page = __page_frag_cache_refill(nc, gfp_mask);
--
2.25.1
