From: Mikulas Patocka <mpatocka@redhat.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: Junaid Shahid <junaids@google.com>,
David Rientjes <rientjes@google.com>,
Alasdair Kergon <agk@redhat.com>,
Mike Snitzer <snitzer@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: [PATCH] dm ioctl: Restore __GFP_HIGH in copy_params()
Date: Mon, 22 May 2017 08:00:11 -0400 (EDT) [thread overview]
Message-ID: <alpine.LRH.2.02.1705220759001.27401@file01.intranet.prod.int.rdu2.redhat.com> (raw)
In-Reply-To: <20170522093725.GF8509@dhcp22.suse.cz>
On Mon, 22 May 2017, Michal Hocko wrote:
> On Fri 19-05-17 19:43:23, Mikulas Patocka wrote:
> >
> >
> > On Fri, 19 May 2017, Michal Hocko wrote:
> >
> > > On Thu 18-05-17 19:50:46, Junaid Shahid wrote:
> > > > (Adding back the correct linux-mm email address and also adding linux-kernel.)
> > > >
> > > > On Thursday, May 18, 2017 01:41:33 PM David Rientjes wrote:
> > > [...]
> > > > > Let's ask Mikulas, who changed this from PF_MEMALLOC to __GFP_HIGH,
> > > > > assuming there was a reason to do it in the first place in two different
> > > > > ways.
> > >
> > > Hmm, the old PF_MEMALLOC used to have the following comment
> > > /*
> > > * Trying to avoid low memory issues when a device is
> > > * suspended.
> > > */
> > >
> > > I am not really sure what that means but __GFP_HIGH certainly have a
> > > different semantic than PF_MEMALLOC. The later grants the full access to
> > > the memory reserves while the prior on partial access. If this is _really_
> > > needed then it deserves a comment explaining why.
> > > --
> > > Michal Hocko
> > > SUSE Labs
> >
> > Sometimes, I/O to a device mapper device is blocked until the userspace
> > daemon dmeventd does some action (for example, when dm-mirror leg fails,
> > dmeventd needs to mark the leg as failed in the lvm metadata and then
> > reload the device).
> >
> > The dmeventd daemon mlocks itself in memory so that it doesn't generate
> > any I/O. But it must be able to call ioctls. __GFP_HIGH is there so that
> > the ioctls issued by dmeventd have higher chance of succeeding if some I/O
> > is blocked, waiting for dmeventd action. It reduces the possibility of
> > low-memory-deadlock, though it doesn't eliminate it entirely.
>
> So what happens if the memory reserves are depleted. Do we deadlock?
Yes, it will deadlock.
> Why is OOM killer insufficient to allow the further progress?
I don't know if the OOM killer will or won't be triggered in this
situation, it depends on the people who wrote the OOM killer.
> --
> Michal Hocko
> SUSE Labs
Mikulas
next prev parent reply other threads:[~2017-05-22 12:01 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 [this message]
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
[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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