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From: Andrew Morton <akpm@linux-foundation.org>
To: Mike Kravetz <mike.kravetz@oracle.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	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>
Subject: Re: [PATCH RESEND 0/8] hugetlb: add demote/split page functionality
Date: Mon, 16 Aug 2021 18:46:11 -0700	[thread overview]
Message-ID: <20210816184611.07b97f4c26b83090f5d48fab@linux-foundation.org> (raw)
In-Reply-To: <b4401912-b59a-2150-feef-468c2d25ba3e@oracle.com>

On Mon, 16 Aug 2021 17:46:58 -0700 Mike Kravetz <mike.kravetz@oracle.com> wrote:

> > It really is a ton of new code.  I think we're owed much more detail
> > about the problem than the above.  To be confident that all this
> > material is truly justified?
> 
> The desired functionality for this specific use case is to simply
> convert a 1G huegtlb page to 512 2MB hugetlb pages.  As mentioned
> 
> "Converting larger to smaller hugetlb pages can be accomplished today by
>  first freeing the larger page to the buddy allocator and then allocating
>  the smaller pages.  However, there are two issues with this approach:
>  1) This process can take quite some time, especially if allocation of
>     the smaller pages is not immediate and requires migration/compaction.
>  2) There is no guarantee that the total size of smaller pages allocated
>     will match the size of the larger page which was freed.  This is
>     because the area freed by the larger page could quickly be
>     fragmented."
> 
> These two issues have been experienced in practice.

Well the first issue is quantifiable.  What is "some time"?  If it's
people trying to get a 5% speedup on a rare operation because hey,
bugging the kernel developers doesn't cost me anything then perhaps we
have better things to be doing.

And the second problem would benefit from some words to help us
understand how much real-world hurt this causes, and how frequently.
And let's understand what the userspace workarounds look like, etc.

> A big chunk of the code changes (aprox 50%) is for the vmemmap
> optimizations.  This is also the most complex part of the changes.
> I added the code as interaction with vmemmap reduction was discussed
> during the RFC.  It is only a performance enhancement and honestly
> may not be worth the cost/risk.  I will get some numbers to measure
> the actual benefit.

Cool.




  reply	other threads:[~2021-08-17  1:46 UTC|newest]

Thread overview: 42+ 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
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 [this message]
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

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