On 20.06.24 23:29, David Hildenbrand wrote:
Currently we always take a folio reference even if migration will not
even be tried or isolation failed, requiring us to grab+drop an additional
reference.
Further, we end up calling folio_likely_mapped_shared() while the folio
might have already been unmapped, because after we dropped the PTL, that
can easily happen. We want to stop touching mapcounts and friends from
such context, and only call folio_likely_mapped_shared() while the folio
is still mapped: mapcount information is pretty much stale and unreliable
otherwise.
So let's move checks into numamigrate_isolate_folio(), rename that
function to migrate_misplaced_folio_prepare(), and call that function
from callsites where we call migrate_misplaced_folio(), but still with
the PTL held.
We can now stop taking temporary folio references, and really only take
a reference if folio isolation succeeded. Doing the
folio_likely_mapped_shared() + golio isolation under PT lock is now similar
to how we handle MADV_PAGEOUT.
While at it, combine the folio_is_file_lru() checks.
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---
Donet just reported an issue. I suspect this fixes it -- in any case, this is
the right thing to do.
From 0833b9896e98c8d88c521609c811a220d14a2e7e Mon Sep 17 00:00:00 2001
From: David Hildenbrand <david@xxxxxxxxxx>
Date: Wed, 26 Jun 2024 18:14:44 +0200
Subject: [PATCH] Fixup: mm/migrate: move NUMA hinting fault folio isolation +
checks under PTL
Donet reports an issue during NUMA migration we haven't seen previously:
[ 71.422804] list_del corruption, c00c00000061b3c8->next is
LIST_POISON1 (5deadbeef0000100)
[ 71.422839] ------------[ cut here ]------------
[ 71.422843] kernel BUG at lib/list_debug.c:56!
[ 71.422850] Oops: Exception in kernel mode, sig: 5 [#1]
We forgot to convert one "return 0;" to return an error instead from
migrate_misplaced_folio_prepare() in case the target node is nearly
full.
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---
mm/migrate.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/migrate.c b/mm/migrate.c
index 8beedbb42a93..9ed43c1eea5e 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2564,7 +2564,7 @@ int migrate_misplaced_folio_prepare(struct folio *folio,
int z;
if (!(sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING))
- return 0;
+ return -EAGAIN;
for (z = pgdat->nr_zones - 1; z >= 0; z--) {
if (managed_zone(pgdat->node_zones + z))
break;
base-commit: 4b17ce353e02b47b00e2fe87b862f09e8b9a47e6
--
2.45.2
--
Cheers,
David / dhildenb
