From: Anshuman Khandual <anshuman.khandual@arm.com>
To: John Hubbard <jhubbard@nvidia.com>, linux-mm@kvack.org
Cc: Andrew Morton <akpm@linux-foundation.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Zi Yan <ziy@nvidia.com>,
linux-kernel@vger.kernel.org
Subject: Re: [RFC] mm/vmstat: Add events for THP migration without split
Date: Fri, 15 May 2020 09:33:54 +0530 [thread overview]
Message-ID: <9cac0480-210c-28de-259e-c17c88e8c899@arm.com> (raw)
In-Reply-To: <8be2c517-ba87-400b-dfbe-461bd6065c2d@nvidia.com>
On 05/14/2020 11:59 PM, John Hubbard wrote:
> On 2020-05-11 21:22, Anshuman Khandual wrote:
>> Add the following new trace events which will help in validating
>> migration events involving PMD based THP pages.
>>
>> 1. THP_PMD_MIGRATION_ENTRY_SET 2. THP_PMD_MIGRATION_ENTRY_REMOVE
>>
>> There are no clear method to confirm whether a THP migration
>> happened with out involving it's split. These trace events along
>> with PGMIGRATE_SUCCESS and PGMIGRATE_FAILURE will provide
>> additional insights. After this change,
>>
>
>
> Hi Anshuman,
>
> It's very nice to see this work, and I think that reporting a bit
> more about THP migration stats is going to make development and
> performance debugging a lot more efficient (and pleasant).
That is definitely one of the motivations for these events here.
>
>
>> A single 2M THP (2K base page) when migrated
>>
>> 1. Without split
>>
>> ................ pgmigrate_success 1 pgmigrate_fail 0
>> ................ thp_pmd_migration_entry_set 1
>> thp_pmd_migration_entry_remove 1 ................
>>
>
> I do think we should decouple the trace event name(s) just a *little*
> more, from the mechanisms used to migrate THPs. In other words, let's
> report the number of THP migration successes, and name it
> accordingly--rather than "set" and "remove", which are pretty
> low-level and furthermore depend on today's exact code.
Agreed, the events are low level and follows the implementation very
closely. Hence posted as a RFC instead, as I was not very sure about
these events.
>
> Maybe Zi Yan's recommended name is exactly right, in fact:
>
> THP_PMD_MIGRATION_SUCCESS
Will also add another THP_PMD_MIGRATION_FAILURE even in migrate_pages()
when a huge page could not be allocated and THP gets split.
prev parent reply other threads:[~2020-05-15 4:04 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-12 4:22 Anshuman Khandual
2020-05-14 14:28 ` Zi Yan
2020-05-15 3:50 ` Anshuman Khandual
2020-05-14 18:29 ` John Hubbard
2020-05-15 4:03 ` Anshuman Khandual [this message]
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