Nick Piggin wrote:
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.
It turns out that setting the pte accessed bit in hardware
can apparently take a few thousand CPU cycles - 3000 cycles
is the number I've heard for one CPU family.
This is a similar number of cycles as is needed to zero out
a page. Giving a cache hot page to userspace could cancel
out the rest of the cost of the page fault handling.
Lets stick with the simpler MADV_DONTNEED code for now and
save the page flag for something else...
--
Politics is the struggle between those who want to make their country
the best in the world, and those who believe it already is. Each group
calls the other unpatriotic.
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