On Wed, 18 Nov 2020 11:46:54 -0800 Jakub Kicinski kuba@kernel.org wrote:
- The kernel is under memory pressure and allocation of
PAGE_FRAG_CACHE_MAX_ORDER in __page_frag_cache_refill() will fail. Instead, the pfmemalloc page is allocated for page_frag_cache->va.
2: All skb->data from page_frag_cache->va (pfmemalloc) will have skb->pfmemalloc=true. The skb will always be dropped by sock without SOCK_MEMALLOC. This is an expected behaviour.
- Suppose a large amount of pages are reclaimed and kernel is not under
memory pressure any longer. We expect skb->pfmemalloc drop will not happen.
- Unfortunately, page_frag_alloc() does not proactively re-allocate
page_frag_alloc->va and will always re-use the prior pfmemalloc page. The skb->pfmemalloc is always true even kernel is not under memory pressure any longer.
Fix this by freeing and re-allocating the page instead of recycling it.
Andrew, are you taking this via -mm or should I put it in net? I'm sending a PR to Linus tomorrow.
Please go ahead - if/when it appears in mainline or linux-next, I'll drop the -mm copy.