[lkml]   [2006]   [Jun]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [patch 0/5] [PATCH,RFC] vfs: per-superblock unused dentries list (2nd version)
On Mon, Jun 19, 2006 at 10:27:39AM +1000, Neil Brown wrote:
> On Monday June 19, wrote:
> >
> > > I can see that shrink_dcache_sb could take a long time and should be
> > > fixed, which should be as simple as replacing it with
> > > shrink_dcache_parent; shrink_dcache_anon.
> >
> > But these are not guaranteed to reclaim all the dentries from a given
> > superblock. Yes, they move the dentries to the LRU, but other activity in the
> > system means that they may not get reclaimed during the subsequent calls
> > to prune_dcache() and hence they may live beyond the unmount....
> >
> My proposed patch earlier in this thread (I can post it again if you
> like) addresses exactly this issue. Instead of moving dentries to the
> global LRU, it moves them to a private LRU, and the calls prune_dcache
> on that. So there is no room for other activity to get in the way of
> prune_dcache doing what needs to be done.

Ok. That sounds like it would work.

> > > But I'm still puzzled as to why a long dcache LRU slows down
> > > unmounting.
> > >
> > > Can you give more details?
> >
> > It's not the unmount that slows down - it's the fact that the dcache lock
> > is held for so long that rest of the system halts for time it takes
> > to run shrink_dcache_sb(). We've seen up to 50s to do a (touch fred; rm fred)
> > when the LRU has grown to several million dentries and shrink_dcache_sb()
> > is running. When this happens, it's not uncommon to see every CPU in the
> > machine spinning on the dcache_lock...
> Definitely a problem.
> Maybe it was hoped that the call to cond_resched_lock(&dcache_lock)
> would avoid this, but apparently not.

The first pass over the LRU doesn't even do that....

> I still maintain that we should replace shrink_dcache_sb with calls to
> shrink_dcache_anon and shrink_dcache_parent. That, together with my
> previous patch, should fix this problem quite cleanly. If I send you
> a combined patch against the latest -mm can you test?

Ok. Send me the patch and I'll try to get some tests done on it...


Dave Chinner
Principal Engineer
SGI Australian Software Group
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

 \ /
  Last update: 2006-06-19 03:03    [W:0.123 / U:3.524 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site