From: Michal Hocko <mhocko@kernel.org>
To: Mike Snitzer <snitzer@redhat.com>
Cc: Mikulas Patocka <mpatocka@redhat.com>,
Junaid Shahid <junaids@google.com>,
David Rientjes <rientjes@google.com>,
Alasdair Kergon <agk@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, andreslc@google.com, gthelen@google.com,
vbabka@suse.cz, linux-kernel@vger.kernel.org
Subject: Re: dm ioctl: Restore __GFP_HIGH in copy_params()
Date: Tue, 23 May 2017 08:49:44 +0200 [thread overview]
Message-ID: <20170523064944.GA12818@dhcp22.suse.cz> (raw)
In-Reply-To: <20170522180415.GA25340@redhat.com>
On Mon 22-05-17 14:04:15, Mike Snitzer wrote:
> On Mon, May 22 2017 at 11:03am -0400,
> Michal Hocko <mhocko@kernel.org> wrote:
>
> > On Mon 22-05-17 10:52:44, Mikulas Patocka wrote:
> > >
> > >
> > > On Mon, 22 May 2017, Michal Hocko wrote:
> > [...]
> > > > I am not sure I understand. OOM killer is invoked for _all_ allocations
> > > > <= PAGE_ALLOC_COSTLY_ORDER that do not have __GFP_NORETRY as long as the
> > > > OOM killer is not disabled (oom_killer_disable) and that only happens
> > > > from the PM suspend path which makes sure that no userspace is active at
> > > > the time. AFAIU this is a userspace triggered path and so the later
> > > > shouldn't apply to it and GFP_KERNEL should be therefore sufficient.
> > > > Relying to a portion of memory reserves to prevent from deadlock seems
> > > > fundamentaly broken to me.
> > > >
> > >
> > > The lvm2 was designed this way - it is broken, but there is not much that
> > > can be done about it - fixing this would mean major rewrite. The only
> > > thing we can do about it is to lower the deadlock probability with
> > > __GFP_HIGH (or PF_MEMALLOC that was used some times ago).
>
> Yes, lvm2 was originally designed to to have access to memory reserves
> to ensure forward progress. But if the mm subsystem has improved to
> allow for the required progress without lvm2 trying to stake a claim on
> those reserves then we'll gladly avoid (ab)using them.
>
> > But let me repeat. GFP_KERNEL allocation for order-0 page will not fail.
>
> OK, but will it be serviced immediately? Not failing isn't useful if it
> never completes.
Well, GFP_KERNEL will not guarantee an immediate success of course.
There is nothing like that. Nor __GFP_HIGH will guarantee that, though,
because reserves can get easily depleted by some workloads. You would
have to use a dedicated memory pool to accomplish what you really need.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2017-05-23 6:50 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20170518185040.108293-1-junaids@google.com>
[not found] ` <20170518190406.GB2330@dhcp22.suse.cz>
[not found] ` <alpine.DEB.2.10.1705181338090.132717@chino.kir.corp.google.com>
2017-05-19 2:50 ` [PATCH] dm ioctl: Restore __GFP_HIGH in copy_params() Junaid Shahid
2017-05-19 7:46 ` Michal Hocko
2017-05-19 23:43 ` Mikulas Patocka
2017-05-22 9:37 ` Michal Hocko
2017-05-22 12:00 ` Mikulas Patocka
2017-05-22 12:09 ` Michal Hocko
2017-05-22 14:52 ` Mikulas Patocka
2017-05-22 15:03 ` Michal Hocko
2017-05-22 18:04 ` Mike Snitzer
2017-05-22 20:35 ` David Rientjes
2017-05-22 23:35 ` Mike Snitzer
2017-05-23 6:05 ` Michal Hocko
2017-05-23 16:44 ` Mikulas Patocka
2017-05-25 8:58 ` Michal Hocko
2017-05-23 6:49 ` Michal Hocko [this message]
[not found] ` <alpine.LRH.2.02.1705191949340.17646@file01.intranet.prod.int.rdu2.redhat.com>
[not found] ` <20170520083412.GD11925@dhcp22.suse.cz>
2017-05-20 19:00 ` [PATCH] " Mikulas Patocka
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