From: Michal Hocko <mhocko@kernel.org>
To: Mike Kravetz <mike.kravetz@oracle.com>
Cc: linux-mm@kvack.org, Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
Andrew Morton <akpm@linux-foundation.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH 3/5] mm, hugetlb: do not rely on overcommit limit during migration
Date: Thu, 14 Dec 2017 08:40:53 +0100 [thread overview]
Message-ID: <20171214074053.GC16951@dhcp22.suse.cz> (raw)
In-Reply-To: <ec386202-9bee-e230-1b37-bc05c4cd8f49@oracle.com>
On Wed 13-12-17 15:35:33, Mike Kravetz wrote:
> On 12/04/2017 06:01 AM, Michal Hocko wrote:
[...]
> > Before migration
> > /sys/devices/system/node/node0/hugepages/hugepages-2048kB/free_hugepages:0
> > /sys/devices/system/node/node0/hugepages/hugepages-2048kB/nr_hugepages:1
> > /sys/devices/system/node/node0/hugepages/hugepages-2048kB/surplus_hugepages:0
> > /sys/devices/system/node/node1/hugepages/hugepages-2048kB/free_hugepages:0
> > /sys/devices/system/node/node1/hugepages/hugepages-2048kB/nr_hugepages:0
> > /sys/devices/system/node/node1/hugepages/hugepages-2048kB/surplus_hugepages:0
> >
> > After
> >
> > /sys/devices/system/node/node0/hugepages/hugepages-2048kB/free_hugepages:0
> > /sys/devices/system/node/node0/hugepages/hugepages-2048kB/nr_hugepages:0
> > /sys/devices/system/node/node0/hugepages/hugepages-2048kB/surplus_hugepages:0
> > /sys/devices/system/node/node1/hugepages/hugepages-2048kB/free_hugepages:0
> > /sys/devices/system/node/node1/hugepages/hugepages-2048kB/nr_hugepages:1
> > /sys/devices/system/node/node1/hugepages/hugepages-2048kB/surplus_hugepages:0
> >
> > with the previous implementation, both nodes would have nr_hugepages:1
> > until the page is freed.
>
> With the previous implementation, the migration would have failed unless
> nr_overcommit_hugepages was explicitly set. Correct?
yes
[...]
> In the previous version of this patch, I asked about handling of 'free' huge
> pages. I did a little digging and IIUC, we do not attempt migration of
> free huge pages. The routine isolate_huge_page() has this check:
>
> if (!page_huge_active(page) || !get_page_unless_zero(page)) {
> ret = false;
> goto unlock;
> }
>
> I believe one of your motivations for this effort was memory offlining.
> So, this implies that a memory area can not be offlined if it contains
> a free (not in use) huge page?
do_migrate_range will ignore this free huge page and then we will free
it up in dissolve_free_huge_pages
> Just FYI and may be something we want to address later.
Maybe yes. The free pool might be reserved which would make
dissolve_free_huge_pages to fail. Maybe we can be more clever and
allocate a new huge page in that case.
> My other issues were addressed.
>
> Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Thanks!
--
Michal Hocko
SUSE Labs
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next prev parent reply other threads:[~2017-12-14 7:40 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-04 14:01 [RFC PATCH 0/5] mm, hugetlb: allocation API and migration improvements Michal Hocko
2017-12-04 14:01 ` [RFC PATCH 1/5] mm, hugetlb: unify core page allocation accounting and initialization Michal Hocko
2017-12-13 0:20 ` Mike Kravetz
2017-12-04 14:01 ` [RFC PATCH 2/5] mm, hugetlb: integrate giga hugetlb more naturally to the allocation path Michal Hocko
2017-12-13 0:24 ` Mike Kravetz
2017-12-04 14:01 ` [RFC PATCH 3/5] mm, hugetlb: do not rely on overcommit limit during migration Michal Hocko
2017-12-13 23:35 ` Mike Kravetz
2017-12-14 7:40 ` Michal Hocko [this message]
2017-12-14 20:57 ` Mike Kravetz
2017-12-04 14:01 ` [RFC PATCH 4/5] mm, hugetlb: get rid of surplus page accounting tricks Michal Hocko
2017-12-14 0:45 ` Mike Kravetz
2017-12-14 7:50 ` Michal Hocko
2017-12-14 20:58 ` Mike Kravetz
2017-12-04 14:01 ` [RFC PATCH 5/5] mm, hugetlb: further simplify hugetlb allocation API Michal Hocko
2017-12-14 21:01 ` Mike Kravetz
2017-12-15 9:33 ` [RFC PATCH 0/5] mm, hugetlb: allocation API and migration improvements Michal Hocko
2017-12-20 5:33 ` Naoya Horiguchi
2017-12-20 9:53 ` Michal Hocko
2017-12-20 22:43 ` Mike Kravetz
2017-12-21 7:28 ` Michal Hocko
2017-12-21 23:35 ` Mike Kravetz
2017-12-22 9:48 ` Michal Hocko
2017-12-22 8:58 ` Naoya Horiguchi
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