linux-kernel - Re: [PATCH v2 0/4] Extend migrate_misplaced

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Date:   Tue, 22 Aug 2023 10:47:15 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc:     <akpm@...ux-foundation.org>, <mgorman@...hsingularity.net>,
        <shy828301@...il.com>, <david@...hat.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 0/4] Extend migrate_misplaced_page() to support batch
 migration

Baolin Wang <baolin.wang@...ux.alibaba.com> writes:

> Hi,
>
> Currently, on our ARM servers with NUMA enabled, we found the cross-die latency
> is a little larger that will significantly impact the workload's performance.
> So on ARM servers we will rely on the NUMA balancing to avoid the cross-die
> accessing. And I posted a patchset[1] to support speculative numa fault to
> improve the NUMA balancing's performance according to the principle of data
> locality. Moreover, thanks to Huang Ying's patchset[2], which introduced batch
> migration as a way to reduce the cost of TLB flush, and it will also benefit
> the migration of multiple pages all at once during NUMA balancing.
>
> So we plan to continue to support batch migration in do_numa_page() to improve
> the NUMA balancing's performance, but before adding complicated batch migration
> algorithm for NUMA balancing, some cleanup and preparation work need to do firstly,
> which are done in this patch set. In short, this patchset extends the
> migrate_misplaced_page() interface to support batch migration, and no functional
> changes intended.
>
> In addition, these cleanup can also benefit the compound page's NUMA balancing,
> which was discussed in previous thread[3]. IIUC, for the compound page's NUMA
> balancing, it is possible that partial pages were successfully migrated, so it is
> necessary to return the number of pages that were successfully migrated from
> migrate_misplaced_page().

But I don't find the return number is used except as bool now.

Per my understanding, I still don't find much value of the changes
except as preparation for batch migration in NUMA balancing.  So I still
think it's better to wait for the whole series.  Where we can check why
these changes are necessary for batch migration.  And I think that you
will provide some number to justify the batch migration, including pros
and cons.

--
Best Regards,
Huang, Ying

> This series is based on the latest mm-unstable(d226b59b30cc).
>
> [1] https://lore.kernel.org/lkml/cover.1639306956.git.baolin.wang@linux.alibaba.com/t/#mc45929849b5d0e29b5fdd9d50425f8e95b8f2563
> [2] https://lore.kernel.org/all/20230213123444.155149-1-ying.huang@intel.com/T/#u
> [3] https://lore.kernel.org/all/f8d47176-03a8-99bf-a813-b5942830fd73@arm.com/
>
> Changes from v1:
>  - Move page validation into a new function suggested by Huang Ying.
>  - Change numamigrate_isolate_page() to boolean type.
>  - Update some commit message.
>
> Baolin Wang (4):
>   mm: migrate: factor out migration validation into
>     numa_page_can_migrate()
>   mm: migrate: move the numamigrate_isolate_page() into do_numa_page()
>   mm: migrate: change migrate_misplaced_page() to support multiple pages
>     migration
>   mm: migrate: change to return the number of pages migrated
>     successfully
>
>  include/linux/migrate.h | 15 +++++++---
>  mm/huge_memory.c        | 23 +++++++++++++--
>  mm/internal.h           |  1 +
>  mm/memory.c             | 43 ++++++++++++++++++++++++++-
>  mm/migrate.c            | 64 +++++++++--------------------------------
>  5 files changed, 88 insertions(+), 58 deletions(-)