> When investigation livelock in RHEL3, i found possible badness in
> prune_dcache, which exist in 2.6.24 also.
Have you actually tested with 2.6.24? shrink_dcache_parent() isn't
called from umount anymore. I think this is the commit responsible
for fixing the issue:
commit c636ebdb186bf37f98d3839f69293597723edb36
Author: David Howells <dhowells@xxxxxxxxxx>
Date: Wed Oct 11 01:22:19 2006 -0700
[PATCH] VFS: Destroy the dentries contributed by a superblock on unmounting
Miklos
> situation - system has ~6 mounted filesystem, at 5 FS do some io, and
> one FS start umount.
> shrink_dcache_parent - collect unused dentries after call
> select_parent() and put these dentries into end of LRU for kill.
> but between exit from select_parent() and enter to prune_dcache(,sb)
> some processed add more unused dentries and put to end lru also.
> prune_dcache start skip some dentiries in loop
> >>>>
> while (skip && tmp != &dentry_unused &&
> list_entry(tmp, struct dentry,
> d_lru)->d_sb != sb) {
> skip--;
> tmp = tmp->prev;
> }
>
> >>>
> but not found correct dentry for superblock.
> later condition
> if (tmp == &dentry_unused)
> break;
> not hit - because LRU has additional dentry, and prune_dcache(,sb) kill
> dentry not related to submitted superblock.
> (this first stranges - for me)
>
> but this not all, because count != 0 prune_dcache run in loop and kill
> all dentries not related to submited sb, with can be need many time (in
> my situation ~15min for ~200k dentries).
>
> after exit from prune_dcache - shrink_dcache_parent() do loop and try
> again destroy dentries - which also need some time.
>
> my tests - show changing condition, from
> if (tmp == &dentry_unused)
> break;
> to
> if (tmp == &dentry_unused) || (sb && (list_entry(tmp,
> struct dentry, d_lru)->d_sb != sb))
> break;
> help with live lock - because prune_dcache exit from loop early and move
> required dentries to end of LRU - for easy kill.
>
> Please comment this investigation.
>
> PS. please send copy to me, i not subscribed to list.
>
>
> --
> Alex Lyashkov <Alexey.lyashkov@xxxxxxx>
> Lustre Group, Sun Microsystems
>
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