linux-kernel - Re: [PATCH] mm/vmstat: Add events for PMD based THP migration without split

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Date:   Wed, 3 Jun 2020 12:08:28 -0400
From:   Daniel Jordan <daniel.m.jordan@...cle.com>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     Daniel Jordan <daniel.m.jordan@...cle.com>,
        John Hubbard <jhubbard@...dia.com>, linux-mm@...ck.org,
        hughd@...gle.com, Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Zi Yan <ziy@...dia.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/vmstat: Add events for PMD based THP migration
 without split

On Wed, Jun 03, 2020 at 10:06:31AM +0530, Anshuman Khandual wrote:
> Does this look okay and sufficient ?
> 
> --- a/Documentation/vm/page_migration.rst
> +++ b/Documentation/vm/page_migration.rst
> @@ -253,5 +253,20 @@ 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
> +=====================
> +Following events can be used to quantify page migration.
> +
> +- PGMIGRATE_SUCCESS
> +- PGMIGRATE_FAIL
> +- THP_MIGRATION_SUCCESS
> +- THP_MIGRATION_FAILURE
> +
> +THP_MIGRATION_FAILURE in particular represents an event when a THP could not be
> +migrated as a single entity following an allocation failure and ended up getting
> +split into constituent normal pages before being retried. This event, along with
> +PGMIGRATE_SUCCESS and PGMIGRATE_FAIL will help in quantifying and analyzing THP
> +migration events including both success and failure cases.

Looks great!

> Sure, will update the commit message accordingly.

Thanks.  Hopefully these will help someone in the future.