linux-kernel - Re: [patch 00/27] [rfc] vfs scalability patchset

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Date:	Sat, 25 Apr 2009 09:06:49 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	npiggin@...e.de, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 00/27] [rfc] vfs scalability patchset

On Sat, Apr 25, 2009 at 04:01:43AM -0400, Christoph Hellwig wrote:
> On Sat, Apr 25, 2009 at 05:18:29AM +0100, Al Viro wrote:
> > However, files_lock part 2 looks very dubious - if nothing else, I would
> > expect that you'll get *more* cross-CPU traffic that way, since the CPU
> > where final fput() runs will correlate only weakly (if at all) with one
> > where open() had been done.  So you are getting more cachelines bouncing.
> > I want to see the numbers for this one, and on different kinds of loads,
> > but as it is I've very sceptical.  BTW, could you try to collect stats
> > along the lines of "CPU #i has done N_{i,j} removals from sb list for
> > files that had been in list #j"?
> > 
> > Splitting files_lock on per-sb basis might be an interesting variant, too.
> 
> We should just kill files_lock and s_files completely.  The remaining
> user are may remount r/o checks, and with counters in place not only on
> the vfsmount but also on the superblock we can kill fs_may_remount_ro in
> it's current form.  The only interesting bit left after that is
> mark_files_ro which is so buggy that I'd prefer to kill it including the
> underlying functionality.

Maybe...  What Eric proposed is essentially a reuse of s_list for per-inode
list of struct file.  Presumably with something like i_lock for protection.
So that's not a conflict.
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