linux-kernel - Re: [PATCH 4/6] PM/Hibernate: Rework shrinking of memory

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <200905141949.53108.rjw@sisk.pl>
Date:	Thu, 14 May 2009 19:49:52 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Pavel Machek <pavel@....cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-pm@...ts.linux-foundation.org, fengguang.wu@...el.com,
	linux-kernel@...r.kernel.org, nigel@...onice.net,
	rientjes@...gle.com, linux-mm@...ck.org
Subject: Re: [PATCH 4/6] PM/Hibernate: Rework shrinking of memory

On Thursday 14 May 2009, Pavel Machek wrote:
> 
> > > > > The main point (I thought) was to remove shrink_all_memory().  Instead,
> > > > > we're retaining it and adding even more stuff?
> > > > 
> > > > The idea is that afterwards we can drop shrink_all_memory() once the
> > > > performance problem has been resolved.  Also, we now allocate memory for the
> > > > image using GFP_KERNEL instead of doing it with GFP_ATOMIC after freezing
> > > > devices.  I'd think that's an improvement?
> > > 
> > > Dunno.  GFP_KERNEL might attempt to do writeback/swapout/etc, which
> > > could be embarrassing if the devices are frozen.
> > 
> > They aren't, because the preallocation is done upfront, so once the OOM killer
> > has been taken care of, it's totally safe. :-)
> 
> As is GFP_ATOMIC. Except that GFP_KERNEL will cause catastrophic
> consequences when accounting goes wrong. (New kernel's idea of what is
> on disk will differ from what is _really_ on disk.)
> 
> If accounting is right, GFP_ATOMIC and GFP_KERNEL is equivalent.
> 
> If accounting is wrong, GFP_ATOMIC will fail with NULL, while
> GFP_KERNEL will do something bad.
> 
> I'd keep GFP_ATOMIC (or GFP_NOIO or similar). 

Repeating myself: with this and the next patch applied, we preallocate memory
for the image _before_ freezing devices and therefore it is safe to use
GFP_KERNEL, because the OOM killer has been taken care of by [3/6].

Thanks,
Rafael
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/