linux-kernel - Re: __GFP_REPEAT usage in fq_alloc

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Message-ID: <CANn89iKcHqyr=af2R7WyZRPawXt_bZkFAsbk0W_tkVt9VOGYFQ@mail.gmail.com>
Date:   Mon, 9 Jan 2017 08:00:16 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: __GFP_REPEAT usage in fq_alloc_node

On Mon, Jan 9, 2017 at 2:22 AM, Michal Hocko <mhocko@...nel.org> wrote:
>
> the changelog doesn't mention it but this, unlike other kvmalloc
> conversions is not without functional changes. The kmalloc part
> will be weaker than it is with the original code for !costly (<64kB)
> requests, because we are enforcing __GFP_NORETRY to break out from the
> page allocator which doesn't really fail such a small requests.
>
> Now the question is what those code paths really prefer. Do they really
> want to potentially loop in the page allocator and invoke the OOM killer
> when the memory is short/fragmeted? I mean we can get into a situation
> when no order-3 pages can be compacted and shooting the system down just
> for that reason sounds quite dangerous to me.
>
> So the main question is how hard should we try before falling back to
> vmalloc here?

This patch is fine :

1) Default hash size is 1024 slots, 8192 bytes on 64bit arches.
2) Most of the times, qdisc are setup at boot time.