This is a note to let you know that I've just added the patch titled
mm/compaction: count pages and stop correctly during page isolation
to the 5.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
mm-compaction-count-pages-and-stop-correctly-during-page-isolation.patch
and it can be found in the queue-5.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 38935861d85a4d9a353d1dd5a156c97700e2765d Mon Sep 17 00:00:00 2001
From: Zi Yan <ziy@xxxxxxxxxx>
Date: Fri, 13 Nov 2020 22:51:40 -0800
Subject: mm/compaction: count pages and stop correctly during page isolation
From: Zi Yan <ziy@xxxxxxxxxx>
commit 38935861d85a4d9a353d1dd5a156c97700e2765d upstream.
In isolate_migratepages_block, when cc->alloc_contig is true, we are
able to isolate compound pages. But nr_migratepages and nr_isolated did
not count compound pages correctly, causing us to isolate more pages
than we thought.
So count compound pages as the number of base pages they contain.
Otherwise, we might be trapped in too_many_isolated while loop, since
the actual isolated pages can go up to COMPACT_CLUSTER_MAX*512=16384,
where COMPACT_CLUSTER_MAX is 32, since we stop isolation after
cc->nr_migratepages reaches to COMPACT_CLUSTER_MAX.
In addition, after we fix the issue above, cc->nr_migratepages could
never be equal to COMPACT_CLUSTER_MAX if compound pages are isolated,
thus page isolation could not stop as we intended. Change the isolation
stop condition to '>='.
The issue can be triggered as follows:
In a system with 16GB memory and an 8GB CMA region reserved by
hugetlb_cma, if we first allocate 10GB THPs and mlock them (so some THPs
are allocated in the CMA region and mlocked), reserving 6 1GB hugetlb
pages via /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages will
get stuck (looping in too_many_isolated function) until we kill either
task. With the patch applied, oom will kill the application with 10GB
THPs and let hugetlb page reservation finish.
[ziy@xxxxxxxxxx: v3]
Link: https://lkml.kernel.org/r/20201030183809.3616803-1-zi.yan@xxxxxxxx
Fixes: 1da2f328fa64 ("cmm,thp,compaction,cma: allow THP migration for CMA allocations")
Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Reviewed-by: Yang Shi <shy828301@xxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20201029200435.3386066-1-zi.yan@xxxxxxxx
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
mm/compaction.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1013,8 +1013,8 @@ isolate_migratepages_block(struct compac
isolate_success:
list_add(&page->lru, &cc->migratepages);
- cc->nr_migratepages++;
- nr_isolated++;
+ cc->nr_migratepages += compound_nr(page);
+ nr_isolated += compound_nr(page);
/*
* Avoid isolating too much unless this block is being
@@ -1022,7 +1022,7 @@ isolate_success:
* or a lock is contended. For contention, isolate quickly to
* potentially remove one source of contention.
*/
- if (cc->nr_migratepages == COMPACT_CLUSTER_MAX &&
+ if (cc->nr_migratepages >= COMPACT_CLUSTER_MAX &&
!cc->rescan && !cc->contended) {
++low_pfn;
break;
@@ -1133,7 +1133,7 @@ isolate_migratepages_range(struct compac
if (!pfn)
break;
- if (cc->nr_migratepages == COMPACT_CLUSTER_MAX)
+ if (cc->nr_migratepages >= COMPACT_CLUSTER_MAX)
break;
}
Patches currently in stable-queue which might be from ziy@xxxxxxxxxx are
queue-5.9/mm-compaction-count-pages-and-stop-correctly-during-page-isolation.patch
queue-5.9/mm-compaction-stop-isolation-if-too-many-pages-are-isolated-and-we-have-pages-to-migrate.patch
