On Fri, 28 Sep 2007 16:32:18 -0400 Trond Myklebust <trond.myklebust@xxxxxxxxxx> wrote: > On Fri, 2007-09-28 at 13:10 -0700, Andrew Morton wrote: > > On Fri, 28 Sep 2007 15:52:28 -0400 > > Trond Myklebust <trond.myklebust@xxxxxxxxxx> wrote: > > > > > On Fri, 2007-09-28 at 12:26 -0700, Andrew Morton wrote: > > > > On Fri, 28 Sep 2007 15:16:11 -0400 Trond Myklebust <trond.myklebust@xxxxxxxxxx> wrote: > > > > > Looking back, they were getting caught up in > > > > > balance_dirty_pages_ratelimited() and friends. See the attached > > > > > example... > > > > > > > > that one is nfs-on-loopback, which is a special case, isn't it? > > > > > > I'm not sure that the hang that is illustrated here is so special. It is > > > an example of a bog-standard ext3 write, that ends up calling the NFS > > > client, which is hanging. The fact that it happens to be hanging on the > > > nfsd process is more or less irrelevant here: the same thing could > > > happen to any other process in the case where we have an NFS server that > > > is down. > > > > hm, so ext3 got stuck in nfs via __alloc_pages direct reclaim? > > > > We should be able to fix that by marking the backing device as > > write-congested. That'll have small race windows, but it should be a 99.9% > > fix? > > No. The problem would rather appear to be that we're doing > per-backing_dev writeback (if I read sync_sb_inodes() correctly), but > we're measuring variables which are global to the VM. The backing device > that we are selecting may not be writing out any dirty pages, in which > case, we're just spinning in balance_dirty_pages_ratelimited(). OK, so it's unrelated to page reclaim. > Should we therefore perhaps be looking at adding per-backing_dev stats > too? That's what mm-per-device-dirty-threshold.patch and friends are doing. Whether it works adequately is not really known at this time. Unfortunately kernel developers don't test -mm much. _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
