From: Mike Kravetz <mike.kravetz@oracle.com>
To: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Cc: David Hildenbrand <david@redhat.com>,
Michal Hocko <mhocko@suse.com>,
Oscar Salvador <osalvador@suse.de>, Zi Yan <ziy@nvidia.com>,
Muchun Song <songmuchun@bytedance.com>,
Naoya Horiguchi <naoya.horiguchi@linux.dev>,
David Rientjes <rientjes@google.com>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 5/8] hugetlb: document the demote sysfs interfaces
Date: Tue, 21 Sep 2021 10:17:35 -0700 [thread overview]
Message-ID: <f602af2c-1055-1eff-3071-cca891d779b7@oracle.com> (raw)
In-Reply-To: <87bl4m9gsw.fsf@linux.ibm.com>
On 9/21/21 6:52 AM, Aneesh Kumar K.V wrote:
> Mike Kravetz <mike.kravetz@oracle.com> writes:
>
>> Describe demote and demote_size interfaces.
>>
>> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
>> ---
>> Documentation/admin-guide/mm/hugetlbpage.rst | 29 ++++++++++++++++++--
>> 1 file changed, 27 insertions(+), 2 deletions(-)
>>
>> diff --git a/Documentation/admin-guide/mm/hugetlbpage.rst b/Documentation/admin-guide/mm/hugetlbpage.rst
>> index 8abaeb144e44..902059a0257b 100644
>> --- a/Documentation/admin-guide/mm/hugetlbpage.rst
>> +++ b/Documentation/admin-guide/mm/hugetlbpage.rst
>> @@ -234,8 +234,12 @@ will exist, of the form::
>>
>> hugepages-${size}kB
>>
>> -Inside each of these directories, the same set of files will exist::
>> +Inside each of these directories, the set of files contained in ``/proc``
>> +will exist. In addition, two additional interfaces for demoting huge
>> +pages will exist::
>>
>> + demote
>> + demote_size
>> nr_hugepages
>> nr_hugepages_mempolicy
>> nr_overcommit_hugepages
>> @@ -243,7 +247,28 @@ Inside each of these directories, the same set of files will exist::
>> resv_hugepages
>> surplus_hugepages
>>
>> -which function as described above for the default huge page-sized case.
>> +The demote interfaces provide the ability to split a huge page into
>> +smaller huge pages. For example, the x86 architecture supports both
>> +1GB and 2MB huge pages sizes. A 1GB huge page can be split into 512
>> +2MB huge pages. The demote interfaces are:
>> +
>> +demote_size
>> + is the size of demoted pages. When a page is demoted a corresponding
>> + number of huge pages of demote_size will be created. For huge pages
>> + of the smallest supported size (2MB on x86), demote_size will be the
>> + system page size (PAGE_SIZE). If demote_size is the system page size
>> + then demoting a page will simply free the huge page. demote_size is
>> + a read only interface.
>
> That is an alternate interface for nr_hugepages. Will it be better to
> return EINVAL on write to 'demote' file below
> /sys/kernel/mm/hugepages/hugepages-2048kB ?
>
> Or may be not expose demote possibility within 2M hugepage directory at all?
>
Thanks for taking a look Aneesh!
You are right. If demote_size is PAGE_SIZE, then demote is just an
alternative to freeing huge pages via the nr_hugepages interface.
So, why even provide such an interface?
It certainly would be easy to just not display demote interfaces for the
smallest huge page size.
Based on other feedback, I am also making demote_size writable. It
makes little sense on x86 with only two huge page sizes. However, it
might be useful on other architectures with more sizes. demote_size can
only be a valid huge page size. Before your comment, I was going to
allow setting demote_size to PAGE_SIZE. Perhaps, that should not be
allowed.
Thanks for the suggestion, I think removing support for demote_size ==
PAGE_SIZE will make the code simpler.
--
Mike Kravetz
next prev parent reply other threads:[~2021-09-21 17:17 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-16 22:49 [PATCH RESEND 0/8] hugetlb: add demote/split page functionality Mike Kravetz
2021-08-16 22:49 ` [PATCH 1/8] hugetlb: add demote hugetlb page sysfs interfaces Mike Kravetz
2021-08-16 22:49 ` [PATCH 2/8] hugetlb: add HPageCma flag and code to free non-gigantic pages in CMA Mike Kravetz
2021-08-16 22:49 ` [PATCH 3/8] hugetlb: add demote bool to gigantic page routines Mike Kravetz
2021-08-16 22:49 ` [PATCH 4/8] hugetlb: add hugetlb demote page support Mike Kravetz
2021-08-16 22:49 ` [PATCH 5/8] hugetlb: document the demote sysfs interfaces Mike Kravetz
2021-08-16 23:28 ` Andrew Morton
2021-08-17 1:04 ` Mike Kravetz
2021-09-21 13:52 ` Aneesh Kumar K.V
2021-09-21 17:17 ` Mike Kravetz [this message]
2021-08-16 22:49 ` [PATCH 6/8] hugetlb: vmemmap optimizations when demoting hugetlb pages Mike Kravetz
2021-08-16 22:49 ` [PATCH 7/8] hugetlb: prepare destroy and prep routines for vmemmap optimized pages Mike Kravetz
2021-08-16 22:49 ` [PATCH 8/8] hugetlb: Optimized demote vmemmap optimizatized pages Mike Kravetz
2021-08-16 23:23 ` [PATCH RESEND 0/8] hugetlb: add demote/split page functionality Andrew Morton
2021-08-17 0:17 ` Mike Kravetz
2021-08-17 0:39 ` Andrew Morton
2021-08-17 0:58 ` Mike Kravetz
2021-08-16 23:27 ` Andrew Morton
2021-08-17 0:46 ` Mike Kravetz
2021-08-17 1:46 ` Andrew Morton
2021-08-17 7:30 ` David Hildenbrand
2021-08-17 16:19 ` Mike Kravetz
2021-08-17 18:49 ` David Hildenbrand
2021-08-24 22:08 ` Mike Kravetz
2021-08-26 7:32 ` Hillf Danton
2021-08-27 17:22 ` Vlastimil Babka
2021-08-27 23:04 ` Mike Kravetz
2021-08-30 10:11 ` Vlastimil Babka
2021-09-02 18:17 ` Mike Kravetz
2021-09-06 14:40 ` Vlastimil Babka
2021-09-07 8:50 ` Hillf Danton
2021-09-08 21:00 ` Mike Kravetz
2021-09-09 4:07 ` Hillf Danton
2021-09-09 11:54 ` Michal Hocko
2021-09-09 13:45 ` Vlastimil Babka
2021-09-09 21:31 ` Mike Kravetz
2021-09-10 8:20 ` Michal Hocko
2021-09-11 0:11 ` Mike Kravetz
2021-09-11 3:11 ` Hillf Danton
2021-09-13 15:50 ` Michal Hocko
2021-09-15 16:57 ` Mike Kravetz
2021-09-17 20:44 ` Mike Kravetz
-- strict thread matches above, loose matches on Subject: below --
2021-07-21 23:05 [PATCH " Mike Kravetz
2021-07-21 23:05 ` [PATCH 5/8] hugetlb: document the demote sysfs interfaces Mike Kravetz
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