Re: [PATCH] Fix dcache race during umount

[Neil Brown]

On Thursday June 22, dhowells@xxxxxxxxxx wrote:
> 
> Hi Neil,
> 
> I'd like to propose an alternative to your patch to fix the dcache race
> between unmounting a filesystem and the memory shrinker.
> 
> In my patch, generic_shutdown_super() is made to call shrink_dcache_sb()
> instead of shrink_dcache_anon(), and the latter function is discarded
> completely since it's no longer used.

Is that a good idea?
I was under the impression that on large machines, the shear size of
the dentry_unused list makes scanning all of it under the dcache_lock
an unpleasant thing to do.

Do you not have easy access to the roots of all trees in your
super-block-sharing situation so that shrink_dcache_parent can be
called on them all?

I would have thought that we want to get rid of shrink_dcache_sb rather
than create more users of it ??

> 
> I feel that prune_dcache() should probably at some point be merged into its
> two callers, since shrink_dcache_parent() and select_parent() can probably
> then do a better job of eating a dentry subtree from the leaves inwards, but I
> haven't attempted that with this patch.
> 

I think this is true, prune_dcache is serving two masters and is
overly complex as a result.

NeilBrown
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