Messages in this thread | | | Date | Mon, 28 Jul 2008 16:41:24 -0700 | From | Andrew Morton <> | Subject | Re: PERF: performance tests with the split LRU VM in -mm |
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On Mon, 28 Jul 2008 10:57:42 -0400 Rik van Riel <riel@redhat.com> wrote:
> On Thu, 24 Jul 2008 22:25:10 -0400 > Rik van Riel <riel@redhat.com> wrote: > > > TEST 1: dd if=/dev/sda of=/dev/null bs=1M > > > > kernel speed swap used > > > > 2.6.26 111MB/s 500kB > > -mm 110MB/s 59MB (ouch, system noticably slower) > > noforce 111MB/s 128kB > > stream 108MB/s 0 (slight regression, not sure why yet) > > > > This patch shows that the split LRU VM in -mm has a problem > > with large streaming IOs: the working set gets pushed out of > > memory, which makes doing anything else during the big streaming > > IO kind of painful. > > > > However, either of the two patches posted fixes that problem, > > though at a slight performance penalty for the "stream" patch. > > OK, the throughput number with this test turns out not to mean > nearly as much as I thought. > > Switching off CPU frequency scaling, pinning the CPUs at the > highest speed, resulted in a throughput of only 102MB/s. > > My suspicion is that faster running code on the CPU results > in IOs being sent down to the device faster, resulting in > smaller IOs and lower throughput. > > This would be promising for the "stream" patch, which makes > choosing between the two patches harder :) > > Andrew, what is your preference between: > http://lkml.org/lkml/2008/7/15/465 > and > http://marc.info/?l=linux-mm&m=121683855132630&w=2 >
Boy. They both seem rather hacky special-cases. But that doesn't mean that they're undesirable hacky special-cases. I guess the second one looks a bit more "algorithmic" and a bit less hacky-special-case. But it all depends on testing..
On a different topic, these:
vmscan-give-referenced-active-and-unmapped-pages-a-second-trip-around-the-lru.patch vm-dont-run-touch_buffer-during-buffercache-lookups.patch
have been floating about in -mm for ages, awaiting demonstration that they're a net benefit. But all of this new page-reclaim rework was built on top of those two patches and incorporates and retains them.
I could toss them out, but that would require some rework and would partially invalidate previous testing and who knows, they _might_ be good patches. Or they might not be.
What are your thoughts?
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