Messages in this thread | | | Date | Wed, 29 Apr 2009 13:06:20 -0400 | From | Christoph Hellwig <> | Subject | Re: [PATCH] vmscan: evict use-once pages first |
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On Tue, Apr 28, 2009 at 08:36:51PM -0700, Elladan wrote: > Rik, > > This patch appears to significantly improve application latency while a large > file copy runs. I'm not seeing behavior that implies continuous bad page > replacement. > > I'm still seeing some general lag, which I attribute to general filesystem > slowness. For example, latencytop sees many events like these: > > down xfs_buf_lock _xfs_buf_find xfs_buf_get_flags 1475.8 msec 5.9 %
This actually is contention on the buffer lock, and most likely happens because it's trying to access a buffer that's beeing read in currently.
> > xfs_buf_iowait xfs_buf_iostart xfs_buf_read_flags 1740.9 msec 2.6 %
That's an actual metadata read.
> Writing a page to disk 1042.9 msec 43.7 % > > It also occasionally sees long page faults: > > Page fault 2068.3 msec 21.3 % > > I guess XFS (and the elevator) is just doing a poor job managing latency > (particularly poor since all the IO on /usr/bin is on the reader disk).
The filesystem doesn't really decide which priorities to use, except for some use of the WRITE_SYNC which is used rather minimall in XFS in 2.6.28.
> Creating block layer request 451.4 msec 14.4 %
I guess that a wait in get_request because we're above nr_requests..
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