Re: Page cache write performance issue

[Nick Piggin]

Nathan Scott wrote:

> On Wed, Oct 13, 2004 at 12:02:06AM -0700, Andrew Morton wrote:
>
> > Well something else if fishy: how can you possibly achieve only 4MB/sec? 
>
> These are 1K writes too remember, so it feels a bit like we
> write 'em out one at a time, sync (though no O_SYNC, or fsync,
> or such involved here).  This is on an i686, so 4K pages, and
> using 4K filesystem blocksizes (both xfs and ext2).

Still shouldn't cause such a big slowdown. Seems like they
might be getting written off the end of the page reclaim
LRU (although in that case it is a bit odd that increasing
the dirty thresholds are improving performance).

I don't think we have any vmscan metrics for this... kswapd
definitely has become more active in 2.6.9-rc. If you're stuck
for ideas, try editing mm/vmscan.c:may_write_to_queue - comment
out the if(current_is_kswapd()) check.

It is a long shot though. Andrew probably has better ideas.

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