linux-kernel - Re: [PATCH net-next 05/12] mm: Make the page_frag_cache allocator handle __GFP

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Message-ID: <CAKgT0Uf2rPRZqQxGDZGkmdUA2j2=2cw0X1k8i0RpKgNxX0tcCw@mail.gmail.com>
Date:   Sat, 27 May 2023 08:54:50 -0700
From:   Alexander Duyck <alexander.duyck@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     David Howells <dhowells@...hat.com>, netdev@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        David Ahern <dsahern@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Jens Axboe <axboe@...nel.dk>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Jeroen de Borst <jeroendb@...gle.com>,
        Catherine Sullivan <csully@...gle.com>,
        Shailend Chand <shailend@...gle.com>,
        Felix Fietkau <nbd@....name>, John Crispin <john@...ozen.org>,
        Sean Wang <sean.wang@...iatek.com>,
        Mark Lee <Mark-MC.Lee@...iatek.com>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Keith Busch <kbusch@...nel.org>, Jens Axboe <axboe@...com>,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        Chaitanya Kulkarni <kch@...dia.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-nvme@...ts.infradead.org
Subject: Re: [PATCH net-next 05/12] mm: Make the page_frag_cache allocator
 handle __GFP_ZERO itself

On Fri, May 26, 2023 at 5:57 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Wed, 24 May 2023 16:33:04 +0100 David Howells wrote:
> > Make the page_frag_cache allocator handle __GFP_ZERO itself rather than
> > passing it off to the page allocator.  There may be a mix of callers, some
> > specifying __GFP_ZERO and some not - and even if all specify __GFP_ZERO, we
> > might refurbish the page, in which case the returned memory doesn't get
> > cleared.
>
> I think it's pretty clear that page frag allocator was never supposed
> to support GFP_ZERO, as we don't need it in networking.. So maybe
> you're better off adding the memset() in nvme?
>
> CCing Alex, who I think would say something along those lines :)
> IDK how much we still care given that most networking drivers are
> migrating to page_poll these days.

Yeah, the page frag allocator wasn't meant to handle things like this.
Generally the cache was meant to be used within one context so that
the GFP flags used were consistent between calls. Currently the only
thing passed appears to be GFP_ATOMIC.

Also I am not a big fan of pulling this out of page_alloc.c The fact
is that is where the allocation functions live so it makes sense to
just leave it there. It isn't as if there is enough code added in my
point of view to create yet another file and make it harder to track
git history as a result.