Re: [PATCH 2/3] mm: make the threshold of enabling THP configurable

[Cong Wang]

ä 2011å06æ21æ 17:36, Mel Gorman åé:
>
> Fragmentation avoidance benefits from tuning min_free_kbytes to a higher
> value and minimising fragmentation-related problems is crucial if THP is
> to allocate its necessary pages.
>
> THP tunes min_free_kbytes automatically and this value is in part
> related to the number of zones. At 512M on a single node machine, the
> recommended min_free_kbytes is close to 10% of memory which is barely
> tolerable as it is. At 256M, it's 17%, at 128M, it's 34% so tuning the
> value lower has diminishing returns as the performance impact of giving
> up such a high percentage of free memory is not going to be offset by
> reduced TLB misses. Tuning it to a higher value might make some sense
> if the higher min_free_kbytes was a problem but it would be much more
> rational to tune it as a sysctl than making it a compile-time decision.

What this patch changed is the check of total memory pages in hugepage_init(),
which I don't think is suitable as a sysctl.

If you mean min_free_kbytes could be tuned as a sysctl, that should be done
in other patch, right? :)

Thanks.
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