From: Mike Kravetz <mike.kravetz@oracle.com>
To: Michal Hocko <mhocko@kernel.org>
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 12:57:54 -0800 [thread overview]
Message-ID: <1ce15f58-4b39-3e03-d0e3-4cd30bcc69b9@oracle.com> (raw)
In-Reply-To: <20171214074053.GC16951@dhcp22.suse.cz>
On 12/13/2017 11:40 PM, Michal Hocko wrote:
> 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.
Don't think we need to try and do anything more clever right now. I was
just a little confused about the hot plug code. Thanks for the explanation.
--
Mike Kravetz
>
>> My other issues were addressed.
>>
>> Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
>
> Thanks!
>
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next prev parent reply other threads:[~2017-12-14 20:58 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
2017-12-14 20:57 ` Mike Kravetz [this message]
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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