linux-kernel - Re: [RFC V2] mm/vmstat: Add events for PMD based THP migration without split

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Message-ID: <20200520071521.GA29616@hori.linux.bs1.fc.nec.co.jp>
Date:   Wed, 20 May 2020 07:15:22 +0000
From:   HORIGUCHI NAOYA(堀口　直也) 
        <naoya.horiguchi@....com>
To:     Anshuman Khandual <anshuman.khandual@....com>
CC:     "linux-mm@...ck.org" <linux-mm@...ck.org>,
        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" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC V2] mm/vmstat: Add events for PMD based THP migration
 without split

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 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
> 
> Cc: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> Cc: Zi Yan <ziy@...dia.com>
> Cc: John Hubbard <jhubbard@...dia.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: linux-mm@...ck.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....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