linux-kernel - [PATCH] mm: migrate: Do not retry 10 times for the subpages of fail-to-migrate THP

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Date:   Thu, 21 Jul 2022 20:05:08 +0800
From:   Baolin Wang <baolin.wang@...ux.alibaba.com>
To:     akpm@...ux-foundation.org
Cc:     ying.huang@...el.com, ziy@...dia.com, shy828301@...il.com,
        baolin.wang@...ux.alibaba.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] mm: migrate: Do not retry 10 times for the subpages of fail-to-migrate THP

If THP is failed to migrate due to -ENOSYS or -ENOMEM case, the THP will
be split, and the subpages of fail-to-migrate THP will be tried to migrate
again, so we should not account the retry counter in the second loop, since
we already accounted 'nr_thp_failed' in the first loop.

Moreover we also do not need retry 10 times for -EAGAIN case for the subpages
of fail-to-migrate THP in the second loop, since we already regarded the
THP as migration failure, and save some migration time (for the worst case,
will try 512 * 10 times) according to previous discussion [1].

[1] https://lore.kernel.org/linux-mm/87r13a7n04.fsf@yhuang6-desk2.ccr.corp.intel.com/

Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
---
Note, this patch is based on the patch set [1] from Huang Ying.
[1] https://lore.kernel.org/linux-mm/20220711084948.274787-1-ying.huang@intel.com/
---
 mm/migrate.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 8429206..e36a084 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1507,7 +1507,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
 			case -EAGAIN:
 				if (is_thp)
 					thp_retry++;
-				else
+				else if (!no_subpage_counting)
 					retry++;
 				nr_retry_pages += nr_subpages;
 				break;
@@ -1533,8 +1533,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
 			}
 		}
 	}
-	if (!no_subpage_counting)
-		nr_failed += retry;
+	nr_failed += retry;
 	nr_thp_failed += thp_retry;
 	nr_failed_pages += nr_retry_pages;
 	/*
-- 
1.8.3.1