linux-kernel - Re: [PATCH v1 0/2] mm: migrate: vm event counter for hugepage migration

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Date:   Thu, 12 Apr 2018 08:18:59 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc:     linux-mm@...ck.org, Zi Yan <zi.yan@...t.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 0/2] mm: migrate: vm event counter for hugepage
 migration

On Wed 11-04-18 17:09:25, Naoya Horiguchi wrote:
> Hi everyone,
> 
> I wrote patches introducing separate vm event counters for hugepage migration
> (both for hugetlb and thp.)
> Hugepage migration is different from normal page migration in event frequency
> and/or how likely it succeeds, so maintaining statistics for them in mixed
> counters might not be helpful both for develors and users.

This is quite a lot of code to be added se we should better document
what it is intended for. Sure I understand your reasonaning about huge
pages are more likely to fail but is this really worth a separate
counter? Do you have an example of how this would be useful?

If we are there then what about different huge page sizes (for hugetlb)?
Do we need per-hstate stats?

In other words, is this really worth it?

>  include/linux/vm_event_item.h |   7 +++
>  mm/migrate.c                  | 103 +++++++++++++++++++++++++++++++++++-------
>  mm/vmstat.c                   |   8 ++++
>  3 files changed, 102 insertions(+), 16 deletions(-)

-- 
Michal Hocko
SUSE Labs