On Wed, 18 Nov 2020 11:46:54 -0800 Jakub Kicinski <kuba@xxxxxxxxxx> wrote: > > 1. 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. > > > > 3. 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. > > > > 4. 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.
