+cc netdev ML & Alexander
On 3/1/2025 10:03 AM, Haiyang Zhang wrote:
In commit 8218f62c9c9b ("mm: page_frag: use initial zero offset for page_frag_alloc_align()"), the check for fragsz is moved earlier. So when the cache is used up, and if the fragsz > PAGE_SIZE, it won't try to refill, and just return NULL. I tested it with fragsz:8192, cache-size:32768. After the initial four successful allocations, it failed, even there is plenty of free memory in the system.
Hi, Haiyang It seems the PAGE_SIZE is 4K for the tested system? Which drivers or subsystems are passing the fragsz being bigger than PAGE_SIZE to page_frag_alloc_align() related API?
To fix, revert the refill logic like before: the refill is attempted before the check & return NULL.
page_frag API is not really for allocating memory being bigger than PAGE_SIZE as __page_frag_cache_refill() will not try hard enough to allocate order 3 compound page when calling __alloc_pages() and will fail back to allocate base page as the discussed in below: https://lore.kernel.org/all/ead00fb7-8538-45b3-8322-8a41386e7381@huawei.com/
Cc: linyunsheng@huawei.com Cc: stable@vger.kernel.org Fixes: 8218f62c9c9b ("mm: page_frag: use initial zero offset for page_frag_alloc_align()") Signed-off-by: Haiyang Zhang haiyangz@microsoft.com
mm/page_frag_cache.c | 26 +++++++++++++------------- 1 file changed, 13 insertions(+), 13 deletions(-)
diff --git a/mm/page_frag_cache.c b/mm/page_frag_cache.c index d2423f30577e..82935d7e53de 100644 --- a/mm/page_frag_cache.c +++ b/mm/page_frag_cache.c @@ -119,19 +119,6 @@ void *__page_frag_alloc_align(struct page_frag_cache *nc, size = PAGE_SIZE << encoded_page_decode_order(encoded_page); offset = __ALIGN_KERNEL_MASK(nc->offset, ~align_mask); if (unlikely(offset + fragsz > size)) {
if (unlikely(fragsz > PAGE_SIZE)) {/** The caller is trying to allocate a fragment* with fragsz > PAGE_SIZE but the cache isn't big* enough to satisfy the request, this may* happen in low memory conditions.* We don't release the cache page because* it could make memory pressure worse* so we simply return NULL here.*/return NULL;}- page = encoded_page_decode_page(encoded_page);
if (!page_ref_sub_and_test(page, nc->pagecnt_bias)) @@ -149,6 +136,19 @@ void *__page_frag_alloc_align(struct page_frag_cache *nc, /* reset page count bias and offset to start of new frag */ nc->pagecnt_bias = PAGE_FRAG_CACHE_MAX_SIZE + 1; offset = 0;
if (unlikely(fragsz > size)) {/** The caller is trying to allocate a fragment* with fragsz > size but the cache isn't big* enough to satisfy the request, this may* happen in low memory conditions.* We don't release the cache page because* it could make memory pressure worse* so we simply return NULL here.*/return NULL;}nc->pagecnt_bias--;