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To:     Anshuman Khandual <anshuman.khandual@arm.com>
CC:     "linux-mm@kvack.org" <linux-mm@kvack.org>,
        Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
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Subject: Re: [RFC V2] mm/vmstat: Add events for PMD based THP migration
 without split
Thread-Topic: [RFC V2] mm/vmstat: Add events for PMD based THP migration
 without split
Thread-Index: AQHWLN+t0tdY3mXd/ESlj6rXEl97xqiwkxmA
Date:   Wed, 20 May 2020 07:15:22 +0000
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On Mon, May 18, 2020 at 12:12:36PM +0530, Anshuman Khandual wrote:
> This adds the following two new VM events which will help in validating P=
MD
> based THP migration without split. Statistics reported through these even=
ts
> will help in performance debugging.
>=20
> 1. THP_PMD_MIGRATION_SUCCESS
> 2. THP_PMD_MIGRATION_FAILURE
>=20
> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> Cc: Zi Yan <ziy@nvidia.com>
> Cc: John Hubbard <jhubbard@nvidia.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: linux-mm@kvack.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>

Hi Anshuman,

I'm neutral for additinal lines in /proc/vmstat. It's a classic (so widely
used) but inflexible interface. Users disabling thp are not happy with many
thp-related lines, but judging from the fact that we already have many
thp-related lines some users really need them. So I feel hard to decide to
agree or disagree with additional lines.

I think that tracepoints are the more flexible interfaces for monitoring,
so I'm interested more in whether thp migration could be monitorable via
tracepoint. Do you have any idea/plan on it?

Thanks,
Naoya Horiguchi=