linux-kernel - Re: __GFP_REPEAT usage in fq_alloc

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Message-ID: <20170109174511.GA8306@dhcp22.suse.cz>
Date:   Mon, 9 Jan 2017 18:45:11 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: __GFP_REPEAT usage in fq_alloc_node

On Mon 09-01-17 08:00:16, Eric Dumazet wrote:
> 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.

What about those non-default configurations. Do they really want to
invoke the OOM killer rather than fallback to the vmalloc?
-- 
Michal Hocko
SUSE Labs