Re: Quadratic behavior of shrink_dcache_parent()

[Rafael J. Wysocki]

On Monday, 20 November 2006 12:10, Miklos Szeredi wrote:
> The shrink_dcache_parent() can take a very long time for deep
> directory trees: minutes for depth of 100,000, probably hours for
> depth of 1,000,000.
> 
> The reason is that after dropping a leaf, it starts again from the
> root.

Oh, well.  So that's the reason why the shrinking of memory in swsusp can
take so much time.

> Filesystems affected include FUSE, NFS, CIFS.  Others I haven't
> checked.  NFS and to a lesser extent CIFS don't seem to efficiently
> handle lookups within such a deep hierarchy, so they're sort of
> immune.
> 
> But with FUSE it's pretty easy to DoS the system.
> 
> Limiting the depth to some sane value could work around this problem,
> but that would mean having to traverse subtrees in rename().
> 
> Any better ideas?

None, for now.  It looks like I need to learn that code ...

Greetings,
Rafael


-- 
You never change things by fighting the existing reality.
		R. Buckminster Fuller
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/