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

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Message-ID: <2d4634ce-9167-6ca6-fb91-f3c671fff672@arm.com>
Date:   Wed, 3 Jun 2020 06:56:57 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     linux-mm@...ck.org, hughd@...gle.com,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Zi Yan <ziy@...dia.com>, John Hubbard <jhubbard@...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 06/02/2020 08:31 PM, Matthew Wilcox wrote:
> On Fri, May 22, 2020 at 09:04:04AM +0530, Anshuman Khandual wrote:
>> This adds the following two new VM events which will help in validating PMD
>> based THP migration without split. Statistics reported through these events
>> will help in performance debugging.
>>
>> 1. THP_PMD_MIGRATION_SUCCESS
>> 2. THP_PMD_MIGRATION_FAILURE
> 
> There's nothing actually PMD specific about these events, is there?
> If we have a THP of a non-PMD size, you'd want that reported through the
> same statistic, wouldn't you?

Yes, there is nothing PMD specific here and we would use the same statistics
for non-PMD size THP migration (if any) as well. But is THP migration really
supported for non-PMD sizes ? CONFIG_ARCH_ENABLE_THP_MIGRATION depends upon
CONFIG_TRANSPARENT_HUGEPAGE without being specific or denying about possible
PUD level support. Fair enough, will drop the PMD from the events and their
functions.