linux-kernel - Re: [RFC 0/3] Recursive reclaim (on __PF

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Date:	Fri, 26 Oct 2007 19:44:09 +0200
From:	Pavel Machek <pavel@....cz>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Christoph Lameter <clameter@....com>,
	Daniel Phillips <phillips@...nq.net>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	dkegel@...gle.com, David Miller <davem@...emloft.net>,
	Nick Piggin <npiggin@...e.de>
Subject: Re: [RFC 0/3] Recursive reclaim (on __PF_MEMALLOC)

Hi!

> > > or
> > > 
> > >   - have a global reserve and selectively serves sockets
> > >     (what I've been doing)
> > 
> > That is a scalability problem on large systems! Global means global 
> > serialization, cacheline bouncing and possibly livelocks. If we get into 
> > this global shortage then all cpus may end up taking the same locks 
> > cycling thought the same allocation paths.
> 
> Dude, breathe, these boxens of yours will never swap over network simply
> because you never configure swap. 
> 
> And, _no_, it does not necessarily mean global serialisation. By simply
> saying there must be N pages available I say nothing about on which node
> they should be available, and the way the watermarks work they will be
> evenly distributed over the appropriate zones.

Agreed. Scalability of emergency swapping reserved is simply
unimportant. Please, lets get swapping to _work_ first, then we can
make it faster.

No, I do not think we'll ever see a livelock on this.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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