linux-kernel - Re: [patch 0/7] [RFC] SLUB: Improve allocpercpu to reduce per cpu access overhead

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Message-Id: <1193999326.27652.348.camel@twins>
Date:	Fri, 02 Nov 2007 11:28:46 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	David Miller <davem@...emloft.net>
Cc:	clameter@....com, akpm@...ux-foundation.org,
	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	mathieu.desnoyers@...ymtl.ca, penberg@...helsinki.fi
Subject: Re: [patch 0/7] [RFC] SLUB: Improve allocpercpu to reduce per cpu
	access overhead

On Thu, 2007-11-01 at 15:58 -0700, David Miller wrote:

> Since you're the one who wants to change the semantics and guarentees
> of this interface, perhaps it might help if you did some greps around
> the tree to see how alloc_percpu() is actually used.  That's what
> I did when I started running into trouble with your patches.

This fancy new BDI stuff also lives off percpu_counter/alloc_percpu().

That means that for example each NFS mount also consumes a number of
words - not quite sure from the top of my head how many, might be in the
order of 24 bytes or something.

I once before started looking at this, because the current
alloc_percpu() can have some false sharing - not that I have machines
that are overly bothered by that. I like the idea of a strict percpu
region, however do be aware of the users.

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