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From: Michal Hocko <mhocko@kernel.org>
To: Mikulas Patocka <mpatocka@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>,
	Shaohua Li <shli@kernel.org>,
	dm-devel@redhat.com
Subject: Re: [PATCH 18/20] dm: clean up GFP_NIO usage
Date: Thu, 28 Apr 2016 16:41:15 +0200	[thread overview]
Message-ID: <20160428144115.GJ31489@dhcp22.suse.cz> (raw)
In-Reply-To: <alpine.LRH.2.02.1604281016520.14065@file01.intranet.prod.int.rdu2.redhat.com>

On Thu 28-04-16 10:20:09, Mikulas Patocka wrote:
> 
> 
> On Thu, 28 Apr 2016, Michal Hocko wrote:
> 
> > From: Michal Hocko <mhocko@suse.com>
> > 
> > copy_params uses GFP_NOIO for explicit allocation requests because this
> > might be called from the suspend path. To quote Mikulas:
> > : The LVM tool calls suspend and resume ioctls on device mapper block
> > : devices.
> > :
> > : When a device is suspended, any bio sent to the device is held. If the
> > : resume ioctl did GFP_KERNEL allocation, the allocation could get stuck
> > : trying to write some dirty cached pages to the suspended device.
> > :
> > : The LVM tool and the dmeventd daemon use mlock to lock its address space,
> > : so the copy_from_user/copy_to_user call cannot trigger a page fault.
> > 
> > Relying on the mlock is quite fragile and we have a better way in kernel
> > to enfore NOIO which is already used for the vmalloc fallback. Just use
> > memalloc_noio_{save,restore} around the whole copy_params function which
> > will force the same also to the page fult paths via copy_{from,to}_user.
> 
> The userspace memory is locked, so we don't need to use memalloc_noio_save 
> around copy_from_user. If the memory weren't locked, memalloc_noio_save 
> wouldn't help us to prevent the IO.

OK, you are right. Got your point. You would have to read from disk to
fault memory in so this is not just about not performing IO during the
reclaim.

So scratch this patch then.

Thanks!
-- 
Michal Hocko
SUSE Labs

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  reply	other threads:[~2016-04-28 14:41 UTC|newest]

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-04-28 13:23 [PATCH 0/19] get rid of superfluous __GFP_REPEAT Michal Hocko
2016-04-28 13:23 ` [PATCH 01/20] tree wide: get rid of __GFP_REPEAT for order-0 allocations part I Michal Hocko
2016-04-28 13:23 ` [PATCH 02/20] x86: get rid of superfluous __GFP_REPEAT Michal Hocko
2016-04-28 13:23 ` [PATCH 03/20] x86/efi: " Michal Hocko
2016-04-28 13:23 ` [PATCH 04/20] arm: " Michal Hocko
2016-04-28 14:55   ` Russell King - ARM Linux
2016-04-28 15:08     ` Michal Hocko
2016-04-29  9:41       ` Michal Hocko
2016-04-28 13:23 ` [PATCH 05/20] arm64: " Michal Hocko
2016-04-28 13:23 ` [PATCH 06/20] arc: " Michal Hocko
2016-04-28 13:23 ` [PATCH 07/20] mips: " Michal Hocko
2016-04-28 13:23 ` [PATCH 08/20] nios2: " Michal Hocko
2016-04-28 13:23 ` [PATCH 09/20] parisc: " Michal Hocko
2016-04-28 13:23 ` [PATCH 10/20] score: " Michal Hocko
2016-04-28 13:23 ` [PATCH 11/20] powerpc: " Michal Hocko
2016-04-28 13:23 ` [PATCH 12/20] sparc: " Michal Hocko
2016-04-28 13:23 ` [PATCH 13/20] s390: " Michal Hocko
2016-04-28 13:24 ` [PATCH 14/20] sh: " Michal Hocko
2016-04-28 13:24 ` [PATCH 15/20] tile: " Michal Hocko
2016-04-28 16:21   ` Chris Metcalf
2016-04-28 13:24 ` [PATCH 16/20] unicore32: " Michal Hocko
2016-04-28 13:24 ` [PATCH 17/20] dm: get rid of superfluous gfp flags Michal Hocko
2016-04-29 18:54   ` Mike Snitzer
2016-05-02  7:31     ` Michal Hocko
2016-04-28 13:24 ` [PATCH 18/20] dm: clean up GFP_NIO usage Michal Hocko
2016-04-28 14:20   ` Mikulas Patocka
2016-04-28 14:41     ` Michal Hocko [this message]
2016-04-28 13:24 ` [PATCH 19/20] md: simplify free_params for kmalloc vs vmalloc fallback Michal Hocko
2016-04-28 14:51   ` [PATCH] " Michal Hocko
2016-04-28 15:04     ` Mikulas Patocka
2016-04-28 15:28       ` Michal Hocko
2016-04-28 15:40         ` Mikulas Patocka
2016-04-28 16:59           ` Michal Hocko
2016-04-28 15:37   ` [PATCH 19/20] " Mike Snitzer
2016-04-28 16:00     ` Michal Hocko
2016-04-28 13:24 ` [PATCH 20/20] jbd2: get rid of superfluous __GFP_REPEAT Michal Hocko
2016-05-12 16:53 ` [PATCH 0/19] " Michal Hocko
2016-05-12 20:13   ` Andrew Morton
2016-05-13  6:58     ` Michal Hocko

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