linux-kernel - Re: [PATCH 7/9] net: use kvmalloc with __GFP

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Message-ID: <20170331084652.GL27098@dhcp22.suse.cz>
Date:   Fri, 31 Mar 2017 10:46:53 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH 7/9] net: use kvmalloc with __GFP_REPEAT rather than open
 coded variant

On Thu 30-03-17 16:21:43, Shakeel Butt wrote:
> On Mon, Mar 6, 2017 at 2:33 AM, Michal Hocko <mhocko@...nel.org> wrote:
> > From: Michal Hocko <mhocko@...e.com>
> >
> > fq_alloc_node, alloc_netdev_mqs and netif_alloc* open code kmalloc
> > with vmalloc fallback. Use the kvmalloc variant instead. Keep the
> > __GFP_REPEAT flag based on explanation from Eric:
> > "
> > At the time, tests on the hardware I had in my labs showed that
> > vmalloc() could deliver pages spread all over the memory and that was a
> > small penalty (once memory is fragmented enough, not at boot time)
> > "
> >
> > The way how the code is constructed means, however, that we prefer to go
> > and hit the OOM killer before we fall back to the vmalloc for requests
> > <=32kB (with 4kB pages) in the current code. This is rather disruptive for
> > something that can be achived with the fallback. On the other hand
> > __GFP_REPEAT doesn't have any useful semantic for these requests. So the
> > effect of this patch is that requests smaller than 64kB will fallback to
> 
> I am a bit confused about this 64kB, shouldn't it be <=32kB (with 4kB
> pages & PAGE_ALLOC_COSTLY_ORDER = 3)?

You are right. I just forgot to update wording. "mm: support
__GFP_REPEAT in kvmalloc_node for >32kB" was fixed but this one stayed
in place.

s@...ller than 64kB@...ch fit into 32kB@

Andrew could you update the changelog please?
-- 
Michal Hocko
SUSE Labs