linux-kernel - Re: [PATCH v2 3/3] percpu: improve allocation success rate for non-GFP

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20170227171404.GP26504@dhcp22.suse.cz>
Date:   Mon, 27 Feb 2017 18:14:04 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Tahsin Erdogan <tahsin@...gle.com>
Cc:     Tejun Heo <tj@...nel.org>, Christoph Lameter <cl@...ux.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Roman Pen <r.peniaev@...il.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        zijun_hu <zijun_hu@....com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        David Rientjes <rientjes@...gle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] percpu: improve allocation success rate for
 non-GFP_KERNEL callers

On Mon 27-02-17 18:07:53, Michal Hocko wrote:
> On Mon 27-02-17 09:01:09, Tahsin Erdogan wrote:
> > On Mon, Feb 27, 2017 at 7:25 AM, Michal Hocko <mhocko@...nel.org> wrote:
> > >         /*
> > >          * No space left.  Create a new chunk.  We don't want multiple
> > >          * tasks to create chunks simultaneously.  Serialize and create iff
> > >          * there's still no empty chunk after grabbing the mutex.
> > >          */
> > >         if (is_atomic)
> > >                 goto fail;
> > >
> > > right before pcpu_populate_chunk so is this actually a problem?
> > 
> > Yes, this prevents adding more pcpu chunks and so cause "atomic" allocations
> > to fail more easily.
> 
> Then I fail to see what is the problem you are trying to fix.

To be more specific. Could you describe what more can we do in the
vmalloc layer for GFP_NOWAIT allocations? They certainly cannot sleep
and cannot perform the reclaim so you have to rely on the background
work.
-- 
Michal Hocko
SUSE Labs