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From: John Hubbard <jhubbard@nvidia.com>
To: Zi Yan <ziy@nvidia.com>, Randy Dunlap <rdunlap@infradead.org>,
	"Anshuman Khandual" <anshuman.khandual@arm.com>,
	Andrew Morton <akpm@linux-foundation.org>
Cc: <linux-mm@kvack.org>, Jonathan Corbet <corbet@lwn.net>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ingo Molnar <mingo@redhat.com>,
	Daniel Jordan <daniel.m.jordan@oracle.com>,
	Hugh Dickins <hughd@google.com>,
	Matthew Wilcox <willy@infradead.org>,
	Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
	<linux-doc@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH V4] mm/vmstat: Add events for THP migration without split
Date: Thu, 9 Jul 2020 13:15:15 -0700
Message-ID: <5968b2ca-98cd-cede-0716-9d44af630dce@nvidia.com> (raw)
In-Reply-To: <C5E3C65C-8253-4638-9D3C-71A61858BB8B@nvidia.com>

On 2020-07-09 10:42, Zi Yan wrote:
...
> diff --git a/Documentation/vm/page_migration.rst b/Documentation/vm/page_migration.rst
> index e65d49f3cf86..68883ac485fa 100644
> --- a/Documentation/vm/page_migration.rst
> +++ b/Documentation/vm/page_migration.rst
> @@ -253,24 +253,32 @@ which are function pointers of struct address_space_operations.
>        PG_isolated is alias with PG_reclaim flag so driver shouldn't use the flag
>        for own purpose.
> 
> -Quantifying Migration
> +Monitoring Migration
>   =====================
> -Following events can be used to quantify page migration.
> -
> -1. PGMIGRATE_SUCCESS       /* Normal page migration success */
> -2. PGMIGRATE_FAIL          /* Normal page migration failure */
> -3. THP_MIGRATION_SUCCESS   /* Transparent huge page migration success */
> -4. THP_MIGRATION_FAILURE   /* Transparent huge page migration failure */
> -5. THP_MIGRATION_SPLIT     /* Transparent huge page got split, retried */
> -
> -THP_MIGRATION_SUCCESS is when THP is migrated successfully without getting
> -split into it's subpages. THP_MIGRATION_FAILURE is when THP could neither
> -be migrated nor be split. THP_MIGRATION_SPLIT is when THP could not
> -just be migrated as is but instead get split into it's subpages and later
> -retried as normal pages. THP events would also update normal page migration
> -statistics PGMIGRATE_SUCCESS and PGMIGRATE_FAILURE. These events will help
> -in quantifying and analyzing various THP migration events including both
> -success and failure cases.
> +
> +The following events (counters) can be used to monitor page migration.
> +
> +1. PGMIGRATE_SUCCESS: Normal page migration success. Each count means that a
> +   page was migrated. If the page was a non-THP page, then this counter is
> +   increased by one. If the page was a THP, then this counter is increased by
> +   the number of THP subpages. For example, migration of a single 2MB THP that
> +   has 4KB-size base pages (subpages) will cause this counter to increase by
> +   512.
> +
> +2. PGMIGRATE_FAIL: Normal page migration failure. Same counting rules as for
> +   _SUCCESS, above: this will be increased by the number of subpages, if it was
> +   a THP.
> +
> +3. THP_MIGRATION_SUCCESS: A THP was migrated without being split.
> +
> +4. THP_MIGRATION_FAIL: A THP could not be migrated nor it could be split.
> +
> +5. THP_MIGRATION_SPLIT: A THP was migrated, but not as such: first, the THP had
> +   to be split. After splitting, a migration retry was used for it's sub-pages.


Just a documentation nit: "its sub-pages", not "it's sub-pages".


thanks,
-- 
John Hubbard
NVIDIA

  reply index

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-09  9:39 Anshuman Khandual
2020-07-09 15:34 ` Randy Dunlap
2020-07-09 16:34   ` Zi Yan
2020-07-09 16:39     ` Randy Dunlap
2020-07-09 17:42       ` Zi Yan
2020-07-09 20:15         ` John Hubbard [this message]
2020-07-09 21:24         ` Randy Dunlap
2020-07-10  3:41         ` Anshuman Khandual
2020-07-24 15:04         ` Daniel Jordan
2020-07-10  3:30   ` Anshuman Khandual
2020-07-10  3:33     ` Randy Dunlap

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