From: Vlastimil Babka <vbabka@suse.cz>
To: Linus Torvalds <torvalds@linux-foundation.org>,
Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>, linux-mm <linux-mm@kvack.org>,
Michal Hocko <mhocko@kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Marc MERLIN <marc@merlins.org>
Subject: Re: [PATCH] block,blkcg: use __GFP_NOWARN for best-effort allocations in blkcg
Date: Wed, 23 Nov 2016 09:50:12 +0100 [thread overview]
Message-ID: <3e8eeadb-8dde-2313-f6e3-ef7763832104@suse.cz> (raw)
In-Reply-To: <CA+55aFwEik1Q-D0d4pRTNq672RS2eHpT2ULzGfttaSWW69Tajw@mail.gmail.com>
On 11/22/2016 11:13 PM, Linus Torvalds wrote:
> On Tue, Nov 22, 2016 at 8:48 AM, Tejun Heo <tj@kernel.org> wrote:
>>
>> Hello,
>>
>> On Tue, Nov 22, 2016 at 04:47:49PM +0100, Vlastimil Babka wrote:
>>> Thanks. Makes me wonder whether we should e.g. add __GFP_NOWARN to
>>> GFP_NOWAIT globally at some point.
>>
>> Yeah, that makes sense. The caller is explicitly saying that it's
>> okay to fail the allocation.
>
> I'm not so convinced about the "atomic automatically means you shouldn't warn".
Right, but atomic allocations should be using GFP_ATOMIC, which allows
to use the atomic reserves. I meant here just GFP_NOWAIT which does not
allow reserves, for allocations that are not in atomic context, but
still don't want to reclaim for performance or whatever reasons, and
have a suitable fallback. It's their choice to not spend any effort on
the allocation and thus they shouldn't spew warnings IMHO.
> You'd certainly _hope_ that atomic allocations either have fallbacks
> or are harmless if they fail, but I'd still rather see that
> __GFP_NOWARN just to make that very much explicit.
A global change to GFP_NOWAIT would of course mean that we should audit
its users (there don't seem to be many), whether they are using it
consciously and should not rather be using GFP_ATOMIC.
Vlastimil
> Because as it is, atomic allocations certainly get to dig deeper into
> our memory reserves, but they most definitely can fail, and I
> definitely see how some code has no fallback because it thinks that
> the deeper reserves mean that it will succeed.
>
> Linus
>
next prev parent reply other threads:[~2016-11-23 8:50 UTC|newest]
Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20161121154336.GD19750@merlins.org>
2016-11-21 21:50 ` 4.8.8 kernel trigger OOM killer repeatedly when I have lots of RAM that should be free Vlastimil Babka
2016-11-21 21:56 ` Marc MERLIN
2016-11-21 23:03 ` [PATCH] block,blkcg: use __GFP_NOWARN for best-effort allocations in blkcg Tejun Heo
2016-11-22 15:47 ` Vlastimil Babka
2016-11-22 16:48 ` Tejun Heo
2016-11-22 22:13 ` Linus Torvalds
2016-11-23 8:50 ` Vlastimil Babka [this message]
2016-11-28 17:19 ` Tejun Heo
2016-11-29 7:25 ` Michal Hocko
2016-11-29 16:38 ` Tejun Heo
2016-11-29 16:57 ` Vlastimil Babka
2016-11-29 17:13 ` Michal Hocko
2016-11-29 17:17 ` Linus Torvalds
2016-11-29 17:28 ` Michal Hocko
2016-11-29 17:48 ` Linus Torvalds
2016-11-22 16:00 ` Jens Axboe
2016-11-22 16:06 ` 4.8.8 kernel trigger OOM killer repeatedly when I have lots of RAM that should be free Marc MERLIN
2016-11-22 16:14 ` Vlastimil Babka
2016-11-22 16:25 ` Michal Hocko
2016-11-22 16:47 ` Marc MERLIN
2016-11-22 16:38 ` Greg Kroah-Hartman
2016-11-29 16:25 ` Michal Hocko
2016-11-29 16:43 ` Patch "mm, oom: stop pre-mature high-order OOM killer invocations" has been added to the 4.8-stable tree gregkh
2016-11-29 16:43 ` 4.8.8 kernel trigger OOM killer repeatedly when I have lots of RAM that should be free Greg Kroah-Hartman
2016-11-22 19:38 ` Linus Torvalds
2016-11-23 6:34 ` Michal Hocko
2016-11-23 6:53 ` Hillf Danton
2016-11-23 7:00 ` Michal Hocko
2016-11-23 9:18 ` Vlastimil Babka
2016-11-28 7:23 ` Michal Hocko
2016-11-28 20:55 ` Marc MERLIN
2016-11-29 15:55 ` Marc MERLIN
2016-11-29 16:07 ` Michal Hocko
2016-11-29 16:34 ` Marc MERLIN
2016-11-29 17:07 ` Linus Torvalds
2016-11-29 17:40 ` Marc MERLIN
2016-11-29 18:01 ` Linus Torvalds
2016-11-30 17:47 ` Marc MERLIN
2016-11-30 18:14 ` Linus Torvalds
2016-11-30 18:21 ` Marc MERLIN
2016-11-30 18:27 ` Jens Axboe
2016-11-30 20:30 ` Tejun Heo
2016-12-01 13:50 ` Kent Overstreet
2016-12-01 18:16 ` Linus Torvalds
2016-12-01 18:30 ` Jens Axboe
2016-12-01 18:37 ` Linus Torvalds
2016-12-01 18:46 ` Jens Axboe
2016-11-29 23:01 ` Marc MERLIN
2016-11-30 13:58 ` Tetsuo Handa
2017-05-02 4:12 ` Marc MERLIN
2017-05-02 7:44 ` Michal Hocko
2017-05-02 14:15 ` Marc MERLIN
2017-05-02 10:44 ` Tetsuo Handa
2016-11-29 16:15 ` Marc MERLIN
2016-11-22 21:46 ` Simon Kirby
2016-11-28 8:06 ` Vlastimil Babka
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