linux-kernel - Re: [PATCH v3 1/1] page_frag: Recover from memory pressure

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Message-Id: <20201118131335.738bdade4f3dfcee190ea8c1@linux-foundation.org>
Date:   Wed, 18 Nov 2020 13:13:35 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Dongli Zhang <dongli.zhang@...cle.com>, linux-mm@...ck.org,
        netdev@...r.kernel.org, willy@...radead.org,
        aruna.ramakrishna@...cle.com, bert.barbe@...cle.com,
        rama.nichanamatlu@...cle.com, venkat.x.venkatsubra@...cle.com,
        manjunath.b.patil@...cle.com, joe.jin@...cle.com,
        srinivas.eeda@...cle.com, stable@...r.kernel.org,
        linux-kernel@...r.kernel.org, davem@...emloft.net,
        edumazet@...gle.com, vbabka@...e.cz
Subject: Re: [PATCH v3 1/1] page_frag: Recover from memory pressure

On Wed, 18 Nov 2020 11:46:54 -0800 Jakub Kicinski <kuba@...nel.org> 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.