On Fri, Feb 25, 2011 at 08:51:49AM +0800, Shaohua Li wrote:

On Thu, 2011-02-24 at 22:04 +0800, Andrea Arcangeli wrote:

quoted

On Thu, Feb 24, 2011 at 04:08:47PM +0800, Shaohua Li wrote:

quoted

with madvise, the min_free_kbytes is still high (same as the 'always'
case). The result is still we have about 50M memory is reserved. you can
try at your machine with boot option 'mem=2G' and check the zoneinfo
output.

yes I know. The objective of that test was exactly to know if the
problem is higher memory footprint because of THP or only the
anti-frag/min_free_kbytes which would still be present with the
"madvise" setting (anti-frag is only shutdown by the "never"
setting). If you still have the out of memory with madvise, then you
can keep THP enabled "always" and then "echo 16384 >
/proc/sys/vm/min_free_kbytes", it should work fine then even with THP
always mode then, no need to disable THP (simply you won't have a good
guarantee that anti-frag is functional so the hugepage usage will be
reduced over time compared to the default min_free_kbytes that enables
anti-frag fully).

I can disable THP or set the min_free_kbytes manually in our test, but
just wonder if it's possible we can avoid the memory waste even with THP
enabled, because this will make more people enable it by default.

With a lower value of min_free_kbytes, THP would give diminishing returns
over time as hugepage allocation success rates start degrading over time. It
might not happen for several days or weeks making it a tricky problem to
diagnose. So yes, the memory waste with THP enabled can be fixed but it
would only be suitable for short-term benchmarks.

If you
don't consider this is a problem, we can disable THP.

-- 
Mel Gorman
SUSE Labs

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