Re: [PATCH 24/25] r/o bind mounts: track number of mount writers

From: Christoph Hellwig
Date: Mon Sep 24 2007 - 15:25:08 EST

On Mon, Sep 24, 2007 at 12:10:35PM -0700, Andrew Morton wrote:
> > As we already say in various messages the percpu counters in here
> > look rather fishy. I'd recomment to take a look at the per-cpu
> > superblock counters in XFS as they've been debugged quite well
> > now and could probably be lifted into a generic library for this
> > kind of think. The code is mostly in fs/xfs/xfs_mount.c can
> > can be spotted by beeing under #ifdef HAVE_PERCPU_SB.
> >
> > It also handles cases like hotplug cpu nicely that this code
> > seems to work around by always iterating over all possible cpus
> > which might not be nice on a dual core laptop with a distro kernel
> > that also has to support big iron.
> hm. How come xfs invented a new version of percpu_counters?

This code actually predates the generic percpu_counters even if it
was merged to mainline later. Neither Dave who wrote it nor me
who reviewed it before it was merged thought of percpu_counters
probably. Then again this code is considerably more complex due
to features actually needed in a very hot fastpath.
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