On Sun, Nov 15, 2020 at 9:16 PM Dongli Zhang dongli.zhang@oracle.com wrote:
The ethernet driver may allocate skb (and skb->data) via napi_alloc_skb(). This ends up to page_frag_alloc() to allocate skb->data from page_frag_cache->va.
During the memory pressure, page_frag_cache->va may be allocated as pfmemalloc page. As a result, the skb->pfmemalloc is always true as skb->data is from page_frag_cache->va. The skb will be dropped if the sock (receiver) does not have SOCK_MEMALLOC. This is expected behaviour under memory pressure.
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References: https://lore.kernel.org/lkml/20201103193239.1807-1-dongli.zhang@oracle.com/ References: https://lore.kernel.org/linux-mm/20201105042140.5253-1-willy@infradead.org/ Suggested-by: Matthew Wilcox (Oracle) willy@infradead.org Cc: Aruna Ramakrishna aruna.ramakrishna@oracle.com Cc: Bert Barbe bert.barbe@oracle.com Cc: Rama Nichanamatlu rama.nichanamatlu@oracle.com Cc: Venkat Venkatsubra venkat.x.venkatsubra@oracle.com Cc: Manjunath Patil manjunath.b.patil@oracle.com Cc: Joe Jin joe.jin@oracle.com Cc: SRINIVAS srinivas.eeda@oracle.com Cc: stable@vger.kernel.org Fixes: 79930f5892e ("net: do not deplete pfmemalloc reserve") Signed-off-by: Dongli Zhang dongli.zhang@oracle.com Acked-by: Vlastimil Babka vbabka@suse.cz
Changed since v1:
- change author from Matthew to Dongli
- Add references to all prior discussions
- Add more details to commit message
Changed since v2:
- add unlikely (suggested by Eric Dumazet)
mm/page_alloc.c | 5 +++++ 1 file changed, 5 insertions(+)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 23f5066bd4a5..91129ce75ed4 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -5103,6 +5103,11 @@ void *page_frag_alloc(struct page_frag_cache *nc, if (!page_ref_sub_and_test(page, nc->pagecnt_bias)) goto refill;
if (unlikely(nc->pfmemalloc)) {free_the_page(page, compound_order(page));goto refill;}
Reviewed-by: Eric Dumazet edumazet@google.com
Thanks !