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

[HORIGUCHI NAOYA(堀口 直也)]

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@xxxxxxxxxxxxx>
> Cc: Zi Yan <ziy@xxxxxxxxxx>
> Cc: John Hubbard <jhubbard@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: linux-mm@xxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>

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