linux-kernel - Re: [PATCH] staging: zcache: reduce tmem bucket lock contention

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Message-ID: <20111003230632.GA12719@kroah.com>
Date:	Mon, 3 Oct 2011 16:06:32 -0700
From:	Greg KH <greg@...ah.com>
To:	Seth Jennings <sjenning@...ux.vnet.ibm.com>
Cc:	gregkh@...e.de, cascardo@...oscopio.com,
	dan.magenheimer@...cle.com, rdunlap@...otime.net,
	devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: zcache: reduce tmem bucket lock contention

On Thu, Sep 29, 2011 at 09:32:26AM -0500, Seth Jennings wrote:
> tmem uses hash buckets each with their own rbtree and lock to
> quickly lookup tmem objects.  tmem has TMEM_HASH_BUCKETS (256)
> buckets per pool.  However, because of the way the tmem_oid is
> generated for frontswap pages, only 16 unique tmem_oids are being
> generated, resulting in only 16 of the 256 buckets being used.
> This cause high lock contention for the per bucket locks.
> 
> This patch changes SWIZ_BITS to include more bits of the offset.
> The result is that all 256 hash buckets are potentially used resulting in a
> 95% drop in hash bucket lock contention.

This patch is somehow corrupted and can't be applied, care to resend it
with Dan's acked-by so that I can apply it?

thanks,

greg k-h
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