From: Mike Snitzer <snitzer@redhat.com>
To: David Rientjes <rientjes@google.com>
Cc: Michal Hocko <mhocko@kernel.org>,
Mikulas Patocka <mpatocka@redhat.com>,
Junaid Shahid <junaids@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: Mon, 22 May 2017 19:35:57 -0400 [thread overview]
Message-ID: <20170522233557.GA26990@redhat.com> (raw)
In-Reply-To: <alpine.DEB.2.10.1705221325200.30407@chino.kir.corp.google.com>
On Mon, May 22 2017 at 4:35pm -0400,
David Rientjes <rientjes@google.com> wrote:
> On Mon, 22 May 2017, Mike Snitzer wrote:
>
> > > > 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.
> >
>
> There is no such improvement to the page allocator when allocating at
> runtime. A persistent amount of memory in a mempool could be set aside as
> a preallocation and unavailable from the rest of the system forever as an
> alternative to dynamically allocating with memory reserves, but that has
> obvious downsides. This patch is the exact right thing to do.
>
> > > 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.
> >
>
> No, and you can use __GFP_HIGH, which this patch does, to have a
> reasonable expectation of forward progress in the very near term.
>
> > While adding the __GFP_NOFAIL flag would serve to document expectations
> > I'm left unconvinced that the memory allocator will _not fail_ for an
> > order-0 page -- as Mikulas said most ioctls don't need more than 4K.
>
> __GFP_NOFAIL would make no sense in kvmalloc() calls, ever, it would never
> fallback to vmalloc :)
>
> I'm hoping this can get merged during the 4.12 window to fix the broken
> commit d224e9381897.
I've added your Acked-by and staged it for 4.12, please see:
https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=for-4.12/dm&id=8c1e2162f27b319da913683143c0c6c09b083ebb
Not sure when I'll send it to Linus but certainly no later than for rc4
inclusion.
Thanks,
Mike
next prev parent reply other threads:[~2017-05-22 23:36 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 [this message]
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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