From: "Huang, Ying" <ying.huang@intel.com>
To: "Zi Yan" <ziy@nvidia.com>
Cc: Yang Shi <shy828301@gmail.com>, <mgorman@suse.de>,
<kirill.shutemov@linux.intel.com>, <mhocko@suse.com>,
<hughd@google.com>, <gerald.schaefer@linux.ibm.com>,
<hca@linux.ibm.com>, <gor@linux.ibm.com>,
<borntraeger@de.ibm.com>, <akpm@linux-foundation.org>,
<linux-mm@kvack.org>, <linux-s390@vger.kernel.org>,
<linux-kernel@vger.kernel.org>
Subject: Re: [v2 PATCH 6/7] mm: migrate: check mapcount for THP instead of ref count
Date: Thu, 15 Apr 2021 14:45:54 +0800 [thread overview]
Message-ID: <87fszsoxjx.fsf@yhuang6-desk1.ccr.corp.intel.com> (raw)
In-Reply-To: <6297AD92-8D0E-4BEC-8E1F-5C5AC32FA128@nvidia.com> (Zi Yan's message of "Wed, 14 Apr 2021 11:02:58 -0400")
"Zi Yan" <ziy@nvidia.com> writes:
> On 13 Apr 2021, at 23:00, Huang, Ying wrote:
>
>> Yang Shi <shy828301@gmail.com> writes:
>>
>>> The generic migration path will check refcount, so no need check refcount here.
>>> But the old code actually prevents from migrating shared THP (mapped by multiple
>>> processes), so bail out early if mapcount is > 1 to keep the behavior.
>>
>> What prevents us from migrating shared THP? If no, why not just remove
>> the old refcount checking?
>
> If two or more processes are in different NUMA nodes, a THP shared by them can be
> migrated back and forth between NUMA nodes, which is quite costly. Unless we have
> a better way of figuring out a good location for such pages to reduce the number
> of migration, it might be better not to move them, right?
>
Some mechanism has been provided in should_numa_migrate_memory() to
identify the shared pages from the private pages. Do you find it
doesn't work well in some situations?
The multiple threads in one process which run on different NUMA nodes
may share pages too. So it isn't a good solution to exclude pages
shared by multiple processes.
Best Regards,
Huang, Ying
next prev parent reply other threads:[~2021-04-15 6:46 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-13 21:24 [v2 RFC PATCH 0/7] mm: thp: use generic THP migration for NUMA hinting fault Yang Shi
2021-04-13 21:24 ` [v2 PATCH 1/7] mm: memory: add orig_pmd to struct vm_fault Yang Shi
2021-05-17 15:09 ` Mel Gorman
2021-05-17 19:39 ` Yang Shi
2021-05-18 7:36 ` Mel Gorman
2021-05-18 17:03 ` Yang Shi
2021-04-13 21:24 ` [v2 PATCH 2/7] mm: memory: make numa_migrate_prep() non-static Yang Shi
2021-05-17 15:11 ` Mel Gorman
2021-04-13 21:24 ` [v2 PATCH 3/7] mm: thp: refactor NUMA fault handling Yang Shi
2021-04-14 2:43 ` Huang, Ying
2021-04-14 17:15 ` Yang Shi
2021-05-17 15:27 ` Mel Gorman
2021-05-17 19:41 ` Yang Shi
2021-04-13 21:24 ` [v2 PATCH 4/7] mm: migrate: account THP NUMA migration counters correctly Yang Shi
2021-05-17 15:28 ` Mel Gorman
2021-04-13 21:24 ` [v2 PATCH 5/7] mm: migrate: don't split THP for misplaced NUMA page Yang Shi
2021-05-17 15:29 ` Mel Gorman
2021-04-13 21:24 ` [v2 PATCH 6/7] mm: migrate: check mapcount for THP instead of ref count Yang Shi
2021-04-14 3:00 ` Huang, Ying
2021-04-14 15:02 ` Zi Yan
2021-04-15 6:45 ` Huang, Ying [this message]
2021-04-15 18:57 ` Zi Yan
2021-04-14 17:23 ` Yang Shi
2021-04-13 21:24 ` [v2 PATCH 7/7] mm: thp: skip make PMD PROT_NONE if THP migration is not supported Yang Shi
2021-05-17 15:30 ` Mel Gorman
2021-05-03 21:58 ` [v2 RFC PATCH 0/7] mm: thp: use generic THP migration for NUMA hinting fault Yang Shi
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