On 11/5/20 5:21 AM, Matthew Wilcox (Oracle) wrote:
When the machine is under extreme memory pressure, the page_frag allocator signals this to the networking stack by marking allocations with the 'pfmemalloc' flag, which causes non-essential packets to be dropped. Unfortunately, even after the machine recovers from the low memory condition, the page continues to be used by the page_frag allocator, so all allocations from this page will continue to be dropped.
Fix this by freeing and re-allocating the page instead of recycling it.
Reported-by: Dongli Zhang dongli.zhang@oracle.com 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")
Your patch looks fine, although this Fixes: tag seems incorrect.
79930f5892e ("net: do not deplete pfmemalloc reserve") was propagating the page pfmemalloc status into the skb, and seems correct to me.
The bug was the page_frag_alloc() was keeping a problematic page for an arbitrary period of time ?
Signed-off-by: Matthew Wilcox (Oracle) willy@infradead.org
mm/page_alloc.c | 4 ++++ 1 file changed, 4 insertions(+)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 778e815130a6..631546ae1c53 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -5139,6 +5139,10 @@ void *page_frag_alloc(struct page_frag_cache *nc, if (!page_ref_sub_and_test(page, nc->pagecnt_bias)) goto refill;
if (nc->pfmemalloc) {
if (unlikely(nc->pfmemalloc)) {
free_the_page(page, compound_order(page));goto refill;}#if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE) /* if size can vary use size else just use PAGE_SIZE */