Messages in this thread | | | Date | Fri, 04 May 2007 20:53:00 +1000 | From | Nick Piggin <> | Subject | Re: [PATCH] MM: implement MADV_FREE lazy freeing of anonymous memory |
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Rik van Riel wrote: > With lazy freeing of anonymous pages through MADV_FREE, performance of > the MySQL sysbench workload more than doubles on my quad-core system.
OK, I've run some tests on a 16 core Opteron system, both sysbench with MySQL 5.33 (set up as described in the freebsd vs linux page), and with ebizzy.
What I found is that, on this system, MADV_FREE performance improvement was in the noise when you look at it on top of the MADV_DONTNEED glibc and down_read(mmap_sem) patch in sysbench.
In ebizzy it was slightly up at low loads and slightly down at high loads, though I wouldn't put as much stock in ebizzy as the real workload, because the numbers are going to be highly dependand on access patterns.
Now these numbers are collected under best-case conditions for MADV_FREE, ie. no page reclaim going on. If you consider page reclaim, then you would think there might be room for regressions.
So far, I'm not convinced this is a good use of a page flag or the added complexity. There are lots of ways we can improve performance using a page flag (my recent PG_waiters, PG_mlock, PG_replicated, etc.) to improve performance, so I think we need some more numbers.
(I'll be away for the weekend...)
LHS is # threads, numbers are +/- 99.9% confidence.
sysbench transactions per sec (higher is better)
2.6.21 1, 453.092000 +/- 7.089284 2, 831.722000 +/- 13.138541 4, 1468.590000 +/- 40.160654 8, 2139.822000 +/- 62.223220 16, 2118.802000 +/- 83.247076 32, 1051.596000 +/- 62.455236 64, 917.078000 +/- 21.086954
new glibc 1, 466.376000 +/- 9.018054 2, 867.020000 +/- 26.163901 4, 1535.880000 +/- 25.784081 8, 2261.856000 +/- 53.350146 16, 2249.020000 +/- 120.361138 32, 1521.858000 +/- 110.236781 64, 1405.262000 +/- 85.260624
mmap_sem 1, 476.144000 +/- 15.865284 2, 871.778000 +/- 12.736486 4, 1529.348000 +/- 21.400517 8, 2235.590000 +/- 54.192125 16, 2177.422000 +/- 27.416498 32, 2120.986000 +/- 58.499708 64, 1949.362000 +/- 51.177977
madv_free 1, 475.056000 +/- 6.943168 2, 861.438000 +/- 22.101826 4, 1564.782000 +/- 55.190110 8, 2211.792000 +/- 59.843995 16, 2163.232000 +/- 46.031627 32, 2100.544000 +/- 86.744497 64, 1947.058000 +/- 62.392049
ebizzy elapsed time (lower is better)
mmap_sem 1, 45.544000 +/- 3.538529 4, 78.492000 +/- 8.881464 16, 224.538000 +/- 7.762784 64, 913.466000 +/- 53.506338
madv_free 1, 43.350000 +/- 0.778292 4, 68.190000 +/- 8.623731 16, 225.568000 +/- 14.940109 64, 899.136000 +/- 56.153209
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