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Message-ID: <f8255302-24d8-4847-a17c-01353f0a39e5@suse.cz>
Date: Tue, 20 Feb 2024 08:43:00 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Baolin Wang <baolin.wang@...ux.alibaba.com>, akpm@...ux-foundation.org
Cc: mgorman@...hsingularity.net, ziy@...dia.com, rostedt@...dmis.org,
mhiramat@...nel.org, mathieu.desnoyers@...icios.com, linux-mm@...ck.org,
linux-trace-kernel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] mm: compaction: update the cc->nr_migratepages when
allocating or freeing the freepages
On 2/20/24 07:16, Baolin Wang wrote:
> Currently we will use 'cc->nr_freepages >= cc->nr_migratepages' comparison
> to ensure that enough freepages are isolated in isolate_freepages(), however
> it just decreases the cc->nr_freepages without updating cc->nr_migratepages
> in compaction_alloc(), which will waste more CPU cycles and cause too many
> freepages to be isolated.
>
> So we should also update the cc->nr_migratepages when allocating or freeing
> the freepages to avoid isolating excess freepages. And I can see fewer free
> pages are scanned and isolated when running thpcompact on my Arm64 server:
> k6.7 k6.7_patched
> Ops Compaction pages isolated 120692036.00 118160797.00
> Ops Compaction migrate scanned 131210329.00 154093268.00
> Ops Compaction free scanned 1090587971.00 1080632536.00
> Ops Compact scan efficiency 12.03 14.26
>
> Moreover, I did not see an obvious latency improvements, this is likely because
> isolating freepages is not the bottleneck in the thpcompact test case.
> k6.7 k6.7_patched
> Amean fault-both-1 1089.76 ( 0.00%) 1080.16 * 0.88%*
> Amean fault-both-3 1616.48 ( 0.00%) 1636.65 * -1.25%*
> Amean fault-both-5 2266.66 ( 0.00%) 2219.20 * 2.09%*
> Amean fault-both-7 2909.84 ( 0.00%) 2801.90 * 3.71%*
> Amean fault-both-12 4861.26 ( 0.00%) 4733.25 * 2.63%*
> Amean fault-both-18 7351.11 ( 0.00%) 6950.51 * 5.45%*
> Amean fault-both-24 9059.30 ( 0.00%) 9159.99 * -1.11%*
> Amean fault-both-30 10685.68 ( 0.00%) 11399.02 * -6.68%*
>
> Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> Acked-by: Mel Gorman <mgorman@...hsingularity.net>
Reviewed-by: Vlastimil Babka <vbabka@...e.cz>
Thanks.
> ---
> Hi Andrew, please use this patch to replace below 2 old patches. Thanks.
> https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git/commit/?h=mm-everything-2024-02-20-04-19&id=cb30899d456d64fb83ee3e3d95cd9fbb18735d87
> https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git/commit/?h=mm-everything-2024-02-20-04-19&id=65713d1c4fc498d35dc1f7c1234ef815aa128429
>
> Changes from v2:
> - Add acked tag from Mel.
> - Fix the mm_compaction_migratepages trace event.
> Changes from v1:
> - Rebased on the latest mm-unstable branch.
> ---
> include/trace/events/compaction.h | 6 +++---
> mm/compaction.c | 12 ++++++++++--
> 2 files changed, 13 insertions(+), 5 deletions(-)
>
> diff --git a/include/trace/events/compaction.h b/include/trace/events/compaction.h
> index 2b2a975efd20..d05759d18538 100644
> --- a/include/trace/events/compaction.h
> +++ b/include/trace/events/compaction.h
> @@ -78,10 +78,10 @@ DEFINE_EVENT(mm_compaction_isolate_template, mm_compaction_fast_isolate_freepage
> #ifdef CONFIG_COMPACTION
> TRACE_EVENT(mm_compaction_migratepages,
>
> - TP_PROTO(struct compact_control *cc,
> + TP_PROTO(unsigned int nr_migratepages,
> unsigned int nr_succeeded),
>
> - TP_ARGS(cc, nr_succeeded),
> + TP_ARGS(nr_migratepages, nr_succeeded),
>
> TP_STRUCT__entry(
> __field(unsigned long, nr_migrated)
> @@ -90,7 +90,7 @@ TRACE_EVENT(mm_compaction_migratepages,
>
> TP_fast_assign(
> __entry->nr_migrated = nr_succeeded;
> - __entry->nr_failed = cc->nr_migratepages - nr_succeeded;
> + __entry->nr_failed = nr_migratepages - nr_succeeded;
> ),
>
> TP_printk("nr_migrated=%lu nr_failed=%lu",
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 4494b2914386..218089b29f13 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -1798,6 +1798,7 @@ static struct folio *compaction_alloc(struct folio *src, unsigned long data)
> dst = list_entry(cc->freepages.next, struct folio, lru);
> list_del(&dst->lru);
> cc->nr_freepages--;
> + cc->nr_migratepages--;
>
> return dst;
> }
> @@ -1813,6 +1814,7 @@ static void compaction_free(struct folio *dst, unsigned long data)
>
> list_add(&dst->lru, &cc->freepages);
> cc->nr_freepages++;
> + cc->nr_migratepages++;
> }
>
> /* possible outcome of isolate_migratepages */
> @@ -2435,7 +2437,7 @@ compact_zone(struct compact_control *cc, struct capture_control *capc)
> unsigned long last_migrated_pfn;
> const bool sync = cc->mode != MIGRATE_ASYNC;
> bool update_cached;
> - unsigned int nr_succeeded = 0;
> + unsigned int nr_succeeded = 0, nr_migratepages;
>
> /*
> * These counters track activities during zone compaction. Initialize
> @@ -2553,11 +2555,17 @@ compact_zone(struct compact_control *cc, struct capture_control *capc)
> pageblock_start_pfn(cc->migrate_pfn - 1));
> }
>
> + /*
> + * Record the number of pages to migrate since the
> + * compaction_alloc/free() will update cc->nr_migratepages
> + * properly.
> + */
> + nr_migratepages = cc->nr_migratepages;
> err = migrate_pages(&cc->migratepages, compaction_alloc,
> compaction_free, (unsigned long)cc, cc->mode,
> MR_COMPACTION, &nr_succeeded);
>
> - trace_mm_compaction_migratepages(cc, nr_succeeded);
> + trace_mm_compaction_migratepages(nr_migratepages, nr_succeeded);
>
> /* All pages were either migrated or will be released */
> cc->nr_migratepages = 0;
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