Re: [patch] mm, thp: always direct reclaim for MADV_HUGEPAGE even when deferred

From: David Rientjes
Date: Wed Dec 28 2016 - 16:34:28 EST

On Wed, 28 Dec 2016, Michal Hocko wrote:

> I do care more about _users_ and their _experience_ than what
> application _writers_ think is the best. This is the whole point
> of giving the defrag tunable. madvise(MADV_HUGEPAGE) is just a hint to
> the system that using transparent hugepages is _preferable_, not
> mandatory. We have an option to allow stalls for those vmas to increase
> the allocation success rate. We also have tunable to completely ignore
> it. And we should also have an option to not stall.

The application developer who uses madvise(MADV_HUGEPAGE) is doing so for
a reason.

We lack the ability to defragment in the background for all users who
don't want to block while allowing madvise(MADV_HUGEPAGE) users to block,
as the changelog for this patch clearly indicates.