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

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Message-ID: <20090514094046.GF6417@elf.ucw.cz>
Date:	Thu, 14 May 2009 11:40:46 +0200
From:	Pavel Machek <pavel@....cz>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
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


> > > > 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). 

								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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