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Some users (hi Zwane) have seen a problem when running a workload that
eats nearly all of physical memory - th system does an OOM kill, even
when there is still a lot of swap free.
The problem appears to be a very big task that is holding the swap
token, and the VM has a very hard time finding any other page in the
system that is swappable.
Instead of ignoring the swap token when sc->priority reaches 0, we could
simply take the swap token away from the memory hog and make sure we
don't give it back to the memory hog for a few seconds.
This patch resolves the problem Zwane ran into.
Signed-off-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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It turns out that the original swap token implementation, by Song Jiang, only
enforced the swap token while the task holding the token is handling a page
fault. This patch approximates that, without adding an additional flag to the
mm_struct, by checking whether the mm->mmap_sem is held for reading, like the
page fault code does.
This patch has the effect of automatically, and gradually, disabling the
enforcement of the swap token when there is little or no paging going on, and
"turning up" the intensity of the swap token code the more the task holding
the token is thrashing.
Thanks to Song Jiang for pointing out this aspect of the token based thrashing
control concept.
The new code shows a slight degradation over the old swap token code, but
still a big win over running without the swap token.
2.6.12+ swap token disabled
$ for i in `seq 10` ; do /usr/bin/time ./qsbench -n 30000000 -p 3 ; done
101.74user 23.13system 8:26.91elapsed 24%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (38597major+430315minor)pagefaults 0swaps
101.98user 24.91system 8:03.06elapsed 26%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (33939major+430457minor)pagefaults 0swaps
101.93user 22.12system 7:34.90elapsed 27%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (33166major+421267minor)pagefaults 0swaps
101.82user 22.38system 8:31.40elapsed 24%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (39338major+433262minor)pagefaults 0swaps
2.6.12+ swap token enabled, timeout 300 seconds
$ for i in `seq 4` ; do /usr/bin/time ./qsbench -n 30000000 -p 3 ; done
102.58user 16.08system 3:41.44elapsed 53%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (19707major+285786minor)pagefaults 0swaps
102.07user 19.56system 4:00.64elapsed 50%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (19012major+299259minor)pagefaults 0swaps
102.64user 18.25system 4:07.31elapsed 48%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (21990major+304831minor)pagefaults 0swaps
101.39user 19.41system 5:15.81elapsed 38%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (24850major+323321minor)pagefaults 0swaps
2.6.12+ with new swap token code, timeout 300 seconds
$ for i in `seq 4` ; do /usr/bin/time ./qsbench -n 30000000 -p 3 ; done
101.87user 24.66system 5:53.20elapsed 35%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (26848major+363497minor)pagefaults 0swaps
102.83user 19.95system 4:17.25elapsed 47%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (19946major+305722minor)pagefaults 0swaps
102.09user 19.46system 5:12.57elapsed 38%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (25461major+334994minor)pagefaults 0swaps
101.67user 20.61system 4:52.97elapsed 41%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (22190major+329508minor)pagefaults 0swaps
Signed-off-by: Rik Van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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