From 2aa339120c7dfe834297a77b13b1a98e12842932 Mon Sep 17 00:00:00 2001 From: David Hildenbrand Date: Tue, 16 Apr 2024 19:25:33 +0200 Subject: [PATCH] mm/ksm: remove page_mapcount() usage in stable_tree_search() We want to limit the use of page_mapcount() to the places where it is absolutely necessary. If our folio has a stable node, it is a (small) KSM folio -- see folio_stable_node(). Let's use folio_mapcount() in stable_tree_search() instead, which results in no functional change. The mapcount > 1 check is a bit confusing, because that's usually a check for page sharing. Looks like the reason is that we are guaranteed to not exceed ksm_max_page_sharing for the tree KSM folio when merging with that. Let's update the documentation to make that clearer. Link: https://lkml.kernel.org/r/20240416172533.663418-1-david@redhat.com Signed-off-by: David Hildenbrand Reviewed-by: Alex Shi Signed-off-by: Andrew Morton --- mm/ksm.c | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) diff --git a/mm/ksm.c b/mm/ksm.c index 486c9974f8e20..159604ad47799 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -1909,12 +1909,15 @@ again: if (page_node) { VM_BUG_ON(page_node->head != &migrate_nodes); /* - * Test if the migrated page should be merged - * into a stable node dup. If the mapcount is - * 1 we can migrate it with another KSM page - * without adding it to the chain. + * If the mapcount of our migrated KSM folio is + * at most 1, we can merge it with another + * KSM folio where we know that we have space + * for one more mapping without exceeding the + * ksm_max_page_sharing limit: see + * chain_prune(). This way, we can avoid adding + * this stable node to the chain. */ - if (page_mapcount(page) > 1) + if (folio_mapcount(folio) > 1) goto chain_append; } -- 2.30.2