Re: [PATCH 8/8] prepare to remove/proc/sys/vm/hugepages_treat_as_movable

From: Naoya Horiguchi
Date: Tue Aug 06 2013 - 00:31:03 EST

On Tue, Aug 06, 2013 at 07:22:02AM +0530, Aneesh Kumar K.V wrote:
> Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> writes:
> >>
> >> Considering that we have architectures that won't support migrating
> >> explicit hugepages with this patch series, is it ok to use
> >> GFP_HIGHUSER_MOVABLE for hugepage allocation ?
> >
> > Originally this parameter was introduced to make hugepage pool on ZONE_MOVABLE.
> > The benefit is that we can extend the hugepage pool more easily,
> > because external fragmentation less likely happens than other zone type
> > by rearranging fragmented pages with page migration/reclaim.
> >
> > So I think using ZONE_MOVABLE for hugepage allocation by default makes sense
> > even on the architectures which don't support hugepage migration.
> But allocating hugepages from ZONE_MOVABLE means we have pages in that
> zone which we can't migrate. Doesn't that impact other features like
> hotplug ?

Memory blocks occupied by hugepages are not removable before this patchset,
whether they are from ZONE_MOVABLE or not, and the hugepage users accepted
it for now. So I think this change doesn't make things worse than now.

It can be more preferable to switch on/off __GFP_MOVABLE flag depending on
archs without using the tunable parameter. I'm ok for this direction, but
I want to do it as a separate work.

Naoya Horiguchi
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