linux-kernel - Re: POHMELFS high performance network filesystem. Transactions, failover, performance.

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Message-ID: <Pine.LNX.4.64.0805140638450.14334@cobra.newdream.net>
Date:	Wed, 14 May 2008 06:41:53 -0700 (PDT)
From:	Sage Weil <sage@...dream.net>
To:	Evgeniy Polyakov <johnpol@....mipt.ru>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: POHMELFS high performance network filesystem. Transactions,
 failover, performance.

> On Wed, May 14, 2008 at 11:40:28AM +0400, Evgeniy Polyakov (johnpol@....mipt.ru) wrote:
> > > If any thread takes more than one kmap() at a time, it is deadlockable.
> > > Because there is a finite pool of kmaps.  Everyone can end up holding
> > > one or more kmaps, then waiting for someone else to release one.
> > 
> > It never takes the whole LAST_PKMAP maps. So the same can be applied to
> > any user who kmaps at least one page - while user waits for free slot,
> > it can be reused by someone else and so on.
> 
> Actually CIFS uses the same logic: maps multiple pages in wrteback path
> and release them after received reply.

Yes.  Only a pagevec at a time, though... apparently 14 is a small enough 
number not to bite too many people in practice?

sage
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