On Wed, 14 May 2008 06:41:53 -0700 (PDT) Sage Weil <sage@xxxxxxxxxxxx> wrote: > > On Wed, May 14, 2008 at 11:40:28AM +0400, Evgeniy Polyakov (johnpol@xxxxxxxxxxx) 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. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
