Messages in this thread | | | Date | Wed, 14 May 2008 10:56:54 -0700 | From | Andrew Morton <> | Subject | Re: POHMELFS high performance network filesystem. Transactions, failover, performance. |
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On Wed, 14 May 2008 06:41:53 -0700 (PDT) Sage Weil <sage@newdream.net> wrote:
> > On Wed, May 14, 2008 at 11:40:28AM +0400, Evgeniy Polyakov (johnpol@2ka.mipt.ru) wrote: > > > > If any thread takes more than one kmap() at a time, it is deadlockable. > > > > Because there is a finite pool of kmaps. Everyone can end up holding > > > > one or more kmaps, then waiting for someone else to release one. > > > > > > It never takes the whole LAST_PKMAP maps. So the same can be applied to > > > any user who kmaps at least one page - while user waits for free slot, > > > it can be reused by someone else and so on. > > > > Actually CIFS uses the same logic: maps multiple pages in wrteback path > > and release them after received reply. > > Yes. Only a pagevec at a time, though... apparently 14 is a small enough > number not to bite too many people in practice? >
In practice you need a large number of threads performing writeout to trigger this. iirc that's how it was demonstrated back in the 2.4 days. Say, thousands of processes/threads doing write+fsync to separate files.
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