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SubjectRe: Page cache write performance issue
Nick Piggin <piggin@cyberone.com.au> wrote:
>
> Andrew probably has better ideas.

uh, is this an ia32 highmem box?

If so, you've hit the VM sour spot. That 128M highmem zone gets 100%
filled with dirty pages and we end up doing a ton of writeout off the page
LRU. And we do that while `dd' is cheerfully writing to a totally
different part of the disk via balance_dirty_pages(). Seekstorm ensues.
Although last time I looked (a long time ago) the slowdown was only 2:1 -
perhaps your disk is in writethrough mode??

Basically, *any* other config is fine. 896MB and below, 1.5GB and above.

I could well understand that a minor kswapd tweak would make this bad
situation worse. Making the dirty ratios really small (dirty_ratio less
than the 128MB) should make it go away.

If it's not ia32 then dunno.
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