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

From: John Hubbard
Date: Tue Jun 02 2020 - 00:48:16 EST

On 2020-06-01 21:20, Anshuman Khandual wrote:
also important: maybe this patch should also be tracking other causes
of THP PMD migration failure, in order to get a truer accounting of the

I hope one of the experts here can weigh in on that...

Is there any other failure reasons which are only specific to THP migration.
Else, adding stats about generic migration failure reasons will just blur
the overall understanding about THP migration successes and failure cases
that results in splitting.

Thinking about that: we do have PGMIGRATE_SUCCESS and PGMIGRATE_FAIL, so I
suppose comparing those numbers with the new THP_PMD_MIGRATION_SUCCESS and
THP_PMD_MIGRATION_FAILURE events should cover it.

However, the fact that this is under discussion hints at the need for a
bit of documentation help. What do you think about adding some notes about
all of this to, say, Documentation/vm/page_migration.rst ?

John Hubbard