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On 02/23/2015 02:16 PM, Andrew Morton wrote:
On Wed, 18 Feb 2015 19:08:12 -0500 Rik van Riel <riel@xxxxxxxxxx>
Here's a live one:If so, this might be rather undesirable behaviour in some
situations (and ditto the current behaviour for pte_none
This can be tuned by adjusting khugepaged_max_ptes_none,
Application does MADV_DONTNEED to free up a load of memory and
then khugepaged comes along and pages that memory back in again.
It seems a bit silly to do this after userspace has deliberately
discarded those pages!
Presumably MADV_NOHUGEPAGE can be used to prevent this, but it's a
bit of a hand-grenade. I guess the MADV_DONTNEED manpage should be
updated to explain all this?
That makes me wonder what a good value for khugepaged_max_ptes_none
Doubling the amount of memory a program uses seems quite unreasonable.
Increasing the amount of memory a program uses by 512x seems totally
Increasing the amount of memory a program uses by 20% might be
reasonable, if that much memory is available, since that seems to
be about how much performance improvement we have ever seen from
Andrew, Andrea, do you have any ideas on this?
Is this something to just set, or should we ask Ebru to run
a few different tests with this?