On Tue, 2011-01-04 at 00:44 -0800, Daniel Stodden wrote: > Hi anyone. > > If somebody's got a sec to enlighten me, there's some phenomenon I > recently came across and found somewhat counterintuitive first. > > Whenever I > > 1. Dirty a bunch of pages backed by an NFS mount on some server. > > 2. Block the traffic with iptables (TCP, assuming that mattered). > Still plenty of writeback pending. > > 3. Sync > > I see #3 drive the dirty count in /proc/meminfo drop back to > almost-zero, immediately. The sync itself blocks, though. > > So the pages are called clean the moment the write got queued, not > acked? Leaving the rest just to retransmits by the socket then? Is this > just done so because one can, or would that order rather matter for > consistency? Take a look at the 'Writeback:' count, which should turn non-zero when you hit #3. The VM allows pages to be either dirty or in writeback, but not both at the same time. This is not NFS-specific. The same rule applies to local filesystems. Cheers Trond -- Trond Myklebust Linux NFS client maintainer NetApp Trond.Myklebust@xxxxxxxxxx www.netapp.com -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
