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authorSean Christopherson <seanjc@google.com>2023-10-27 11:21:56 -0700
committerPaolo Bonzini <pbonzini@redhat.com>2023-11-13 05:31:38 -0500
commit0003e2a414687fff6a75250d381e4abf345d663f (patch)
tree7eca3e93819013585f28865630a850a57cc03a91 /mm/compaction.c
parent5a475554db1e476a14216e742ea2bdb77362d5d5 (diff)
mm: Add AS_UNMOVABLE to mark mapping as completely unmovable
Add an "unmovable" flag for mappings that cannot be migrated under any circumstance. KVM will use the flag for its upcoming GUEST_MEMFD support, which will not support compaction/migration, at least not in the foreseeable future. Test AS_UNMOVABLE under folio lock as already done for the async compaction/dirty folio case, as the mapping can be removed by truncation while compaction is running. To avoid having to lock every folio with a mapping, assume/require that unmovable mappings are also unevictable, and have mapping_set_unmovable() also set AS_UNEVICTABLE. Cc: Matthew Wilcox <willy@infradead.org> Co-developed-by: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Sean Christopherson <seanjc@google.com> Message-Id: <20231027182217.3615211-15-seanjc@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'mm/compaction.c')
-rw-r--r--mm/compaction.c43
1 files changed, 31 insertions, 12 deletions
diff --git a/mm/compaction.c b/mm/compaction.c
index 38c8d216c6a3..12b828aed7c8 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -883,6 +883,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
/* Time to isolate some pages for migration */
for (; low_pfn < end_pfn; low_pfn++) {
+ bool is_dirty, is_unevictable;
if (skip_on_failure && low_pfn >= next_skip_pfn) {
/*
@@ -1080,8 +1081,10 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
if (!folio_test_lru(folio))
goto isolate_fail_put;
+ is_unevictable = folio_test_unevictable(folio);
+
/* Compaction might skip unevictable pages but CMA takes them */
- if (!(mode & ISOLATE_UNEVICTABLE) && folio_test_unevictable(folio))
+ if (!(mode & ISOLATE_UNEVICTABLE) && is_unevictable)
goto isolate_fail_put;
/*
@@ -1093,26 +1096,42 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
if ((mode & ISOLATE_ASYNC_MIGRATE) && folio_test_writeback(folio))
goto isolate_fail_put;
- if ((mode & ISOLATE_ASYNC_MIGRATE) && folio_test_dirty(folio)) {
- bool migrate_dirty;
+ is_dirty = folio_test_dirty(folio);
+
+ if (((mode & ISOLATE_ASYNC_MIGRATE) && is_dirty) ||
+ (mapping && is_unevictable)) {
+ bool migrate_dirty = true;
+ bool is_unmovable;
/*
* Only folios without mappings or that have
- * a ->migrate_folio callback are possible to
- * migrate without blocking. However, we may
- * be racing with truncation, which can free
- * the mapping. Truncation holds the folio lock
- * until after the folio is removed from the page
- * cache so holding it ourselves is sufficient.
+ * a ->migrate_folio callback are possible to migrate
+ * without blocking.
+ *
+ * Folios from unmovable mappings are not migratable.
+ *
+ * However, we can be racing with truncation, which can
+ * free the mapping that we need to check. Truncation
+ * holds the folio lock until after the folio is removed
+ * from the page so holding it ourselves is sufficient.
+ *
+ * To avoid locking the folio just to check unmovable,
+ * assume every unmovable folio is also unevictable,
+ * which is a cheaper test. If our assumption goes
+ * wrong, it's not a correctness bug, just potentially
+ * wasted cycles.
*/
if (!folio_trylock(folio))
goto isolate_fail_put;
mapping = folio_mapping(folio);
- migrate_dirty = !mapping ||
- mapping->a_ops->migrate_folio;
+ if ((mode & ISOLATE_ASYNC_MIGRATE) && is_dirty) {
+ migrate_dirty = !mapping ||
+ mapping->a_ops->migrate_folio;
+ }
+ is_unmovable = mapping && mapping_unmovable(mapping);
folio_unlock(folio);
- if (!migrate_dirty)
+ if (!migrate_dirty || is_unmovable)
goto isolate_fail_put;
}