VM: Automatic page cache reclaim (take 3)

Hi,

Here's the next round of these patches. These are totally different in an attempt to meet the "simpler" request after the last patches. For reference the earlier threads are:

http://marc.theaimsgroup.com/?l=linux-kernel&m=110839604924587&w=2
http://marc.theaimsgroup.com/?l=linux-mm&m=111461480721249&w=2

This set of patches replaces my other vm- patches that are currently in -mm. So they're against 2.6.12-rc5-mm1 about half way through the -mm patchset.

As I said already this patch is a lot simpler. The reclaim is turned on or off on a per-zone basis using a syscall. I haven't tested the x86 syscall, so it might be wrong. It uses the existing reclaim/pageout code with the small addition of a may_swap flag to scan_control (patch 1/4).

I also added __GFP_NORECLAIM (patch 3/4) so that certain allocation types can be flagged to never cause reclaim. This was a deficiency that was in all of my earlier patch sets. Previously, doing a big buffered read would fill one zone with page cache and then start to reclaim from that same zone, leaving the other zones untouched.

Adding some extra throttling on the reclaim was also required (patch 4/4). Without the machine would grind to a crawl when doing a "make -j" kernel build. Even with this patch the System Time is higher on average, but it seems tolerable. Here are some numbers for kernbench runs on a 2-node, 4cpu, 8Gig RAM Altix in the "make -j" run:

			wall  user   sys   %cpu  ctx sw.  sleeps
			----  ----   ---   ----   ------  ------
No patch		1009  1384   847   258   298170   504402
w/patch, no reclaim     880   1376   667   288   254064   396745
w/patch & reclaim       1079  1385   926   252   291625   548873

These numbers are the average of 2 runs of 3 "make -j" runs done right after system boot. Run-to-run variability for "make -j" is huge, so these numbers aren't terribly useful except to seee that with reclaim the benchmark still finishes in a reasonable amount of time.

I also looked at the NUMA hit/miss stats for the "make -j" runs and the reclaim doesn't make any difference when the machine is thrashing away.

Doing a "make -j8" on a single node that is filled with page cache pages takes 700 seconds with reclaim turned on and 735 seconds without reclaim (due to remote memory accesses).

The simple zone_reclaim syscall program is at
http://www.bork.org/~mort/sgi/zone_reclaim.c

Please test or comment!
mh

Martin Hicks   ||   Silicon Graphics Inc.   ||   [email protected]
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