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

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Message-ID: <CALvZod73-ddnbMAWXF9QpXMcpjZMLreLXheUo-CgcB7s_5iBnQ@mail.gmail.com>
Date:   Thu, 30 Mar 2017 16:21:43 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...e.com>,
        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 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)?

> vmalloc easier now.
>
> Cc: Eric Dumazet <edumazet@...gle.com>
> Cc: netdev@...r.kernel.org
> Acked-by: Vlastimil Babka <vbabka@...e.cz>
> Signed-off-by: Michal Hocko <mhocko@...e.com>
> ---