linux-kernel - Re: upcoming kerneloops.org item: get_page_from

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Message-ID: <20090630062720.GA1351@ucw.cz>
Date:	Tue, 30 Jun 2009 08:27:20 +0200
From:	Pavel Machek <pavel@....cz>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	penberg@...helsinki.fi, arjan@...radead.org,
	linux-kernel@...r.kernel.org, cl@...ux-foundation.org,
	npiggin@...e.de, David Rientjes <rientjes@...gle.com>,
	Mel Gorman <mel@....ul.ie>
Subject: Re: upcoming kerneloops.org item: get_page_from_freelist


> > This is not a new concept. oom has never been "immediately kill".
> 
> Well, it has been immediate for a long time.  A couple of reasons which
> I can recall:
> 
> - A page-allocating process will oom-kill another process in the
>   expectation that the killing will free up some memory.  If the
>   oom-killed process remains stuck in the page allocator, that doesn't
>   work.
> 
> - The oom-killed process might be holding locks (typically fs locks).
>   This can cause an arbitrary number of other processes to be blocked.
>   So to get the system unstuck we need the oom-killed process to
>   immediately exit the page allocator, to handle the NULL return and to
>   drop those locks.
> 
> There may be other reasons - it was all a long time ago, and I've never
> personally hacked on the oom-killer much and I never get oom-killed. 
> But given the amount of development work which goes on in there, some
> people must be getting massacred.
> 
> 
> A long time ago, the Suse kernel shipped with a largely (or
> completely?) disabled oom-killer.  It removed the
> retry-small-allocations-for-ever logic and simply returned NULL to the
> caller.  I never really understood what problem/thinking led Andrea to
> do that.

I guess he was trying to get huge 32bit highmem machines to work... On
such systems, kmalloc failures will eventually get you...
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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