linux-kernel - Re: [Bug #13058] First hibernation attempt fails

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Message-ID: <20090420195306.GA3299@elf.ucw.cz>
Date:	Mon, 20 Apr 2009 21:53:06 +0200
From:	Pavel Machek <pavel@....cz>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	torvalds@...ux-foundation.org, jens.axboe@...cle.com,
	alan-jenkins@...fmail.co.uk, rjw@...k.pl,
	linux-kernel@...r.kernel.org, kernel-testers@...r.kernel.org
Subject: Re: [Bug #13058] First hibernation attempt fails

Hi!

> > > And the thing is, that "swsusp_shrink_memory()" is just full of 
> > > heuristics. There's no hard numbers there. It doesn't seem to wait for 
> > > writeout, it just does the equivalent of "shrink_list()" and 
> > > "shrink_slab()", but it seems to have been basically cribbed half-way 
> > > from the regular "try to free memory", without really doing it all.
> > 
> > akpm designed shrink_memory(). Long time ago it was just while (1)
> > kmalloc() loop. It should be waiting. Andrew?
> 
> I always wanted the thing to just allocate all the memory which it
> needed and then to either return it all to the caller or free it all
> again for the caller to reallocate (preferably the former).

We need half of memory free for swsusp to work. If we "just allocate"
it, we will trigger OOM killer; we'd prefer to fail suspend than to
OOM kill.

> But for some reason which I don't recall (Pavel provided it, iirc)
> that

Alas, I do not remember that clearly.

> doesn't work.  So the current (and subsequently tweaked) scheme was put
> in there instead.  It turned out to be surprisingly difficult and ugly
> to graft it in top of the existing page reclaim code, and various
> changes were subsequently made to make it sort-of-work.
> 
> Remind me: why can't we just allocate N pages at suspend-time?

We need half of memory free. The reason we can't "just allocate" is
probably OOM killer; but my memories are quite weak :-(.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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