linux-kernel - Re: [PATCH] mm,memory_hotplug: Explicitly pass the head to isolate_huge

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Message-ID: <20190213151547.cwaqptreai43s65j@d104.suse.de>
Date:   Wed, 13 Feb 2019 16:15:50 +0100
From:   Oscar Salvador <osalvador@...e.de>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Mike Kravetz <mike.kravetz@...cle.com>, akpm@...ux-foundation.org,
        david@...hat.com, anthony.yznaga@...cle.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm,memory_hotplug: Explicitly pass the head to
 isolate_huge_page

On Wed, Feb 13, 2019 at 01:33:39PM +0100, Michal Hocko wrote:
> Why isn't our check in has_unmovable_pages sufficient?

Taking a closer look, it should be enough.
I was mainly confused by the fact that if the zone is ZONE_MOVABLE,
we do not keep checking in has_unmovable_pages():

if (zone_idx(zone) == ZONE_MOVABLE)
	continue;

But I overlooked that htlb_alloc_mask() checks whether the allocation
cand end up in a movable zone.
hugepage_movable_supported() checks that and if the hstate does not
support migration at all, we skip __GFP_MOVABLE.

So I think that the check in has_unmovable_pages() should be more than enough,
so we could strip the checks from do_migrate_ranges() and
scan_movable_pages() regarding hugepage migratability.

I will run some tests just to make sure this holds and then
I will send a patch.

Thanks
-- 
Oscar Salvador
SUSE L3