Since merged pages are copied every time they need to be modified, the
write access time is different between shared and non-shared pages. Add
ksm_cow_time() function which evaluates latency of these COW breaks.
First, 4000 pages are allocated and the time, required to modify 1 byte in
every other page, is measured. After this, the pages are merged into 2000
pairs and in each pair, 1 page is modified (i.e. they are decoupled) to
detect COW breaks. The time needed to break COW of merged pages is then
compared with performance of non-shared pages.
The test is run as follows: ./ksm_tests -C
The output:
Total size: 15 MiB
Not merged pages:
Total time: 0.002185489 s
Average speed: 3202.945 MiB/s
Merged pages:
Total time: 0.004386872 s
Average speed: 1595.670 MiB/s
Link: https://lkml.kernel.org/r/1d03ee0d1b341959d4b61672c6401d498bff5652.1629386192.git.zhansayabagdaulet@gmail.com
Signed-off-by: Zhansaya Bagdauletkyzy <zhansayabagdaulet@gmail.com>
Reviewed-by: Tyler Hicks <tyhicks@linux.microsoft.com>
Reviewed-by: Pavel Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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