Commit [39deaf85: mm: compaction: make isolate_lru_page() filter-aware]
noted that compaction does not migrate dirty or writeback pages and
that is was meaningless to pick the page and re-add it to the LRU list.
This had to be partially reverted because some dirty pages can be
migrated by compaction without blocking.
This patch updates "mm: compaction: make isolate_lru_page" by skipping
over pages that migration has no possibility of migrating to minimise
LRU disruption.
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
---
include/linux/mmzone.h | 2 ++
mm/compaction.c | 3 +++
mm/vmscan.c | 35 +++++++++++++++++++++++++++++++++--
3 files changed, 38 insertions(+), 2 deletions(-)
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 188cb2f..ac5b522 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -173,6 +173,8 @@ static inline int is_unevictable_lru(enum lru_list l)
#define ISOLATE_CLEAN ((__force isolate_mode_t)0x4)
/* Isolate unmapped file */
#define ISOLATE_UNMAPPED ((__force isolate_mode_t)0x8)
+/* Isolate for asynchronous migration */
+#define ISOLATE_ASYNC_MIGRATE ((__force isolate_mode_t)0x10)
/* LRU Isolation modes. */
typedef unsigned __bitwise__ isolate_mode_t;
diff --git a/mm/compaction.c b/mm/compaction.c
index 615502b..0379263 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -349,6 +349,9 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
continue;
}
+ if (!cc->sync)
+ mode |= ISOLATE_ASYNC_MIGRATE;
+
/* Try isolate the page */
if (__isolate_lru_page(page, mode, 0) != 0)
continue;
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 69057b5..16fb177 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1061,8 +1061,39 @@ int __isolate_lru_page(struct page *page, isolate_mode_t mode, int file)
ret = -EBUSY;
- if ((mode & ISOLATE_CLEAN) && (PageDirty(page) || PageWriteback(page)))
- return ret;
+ /*
+ * To minimise LRU disruption, the caller can indicate that it only
+ * wants to isolate pages it will be able to operate on without
+ * blocking - clean pages for the most part.
+ *
+ * ISOLATE_CLEAN means that only clean pages should be isolated. This
+ * is used by reclaim when it is cannot write to backing storage
+ *
+ * ISOLATE_ASYNC_MIGRATE is used to indicate that it only wants to pages
+ * that it is possible to migrate without blocking
+ */
+ if (mode & (ISOLATE_CLEAN|ISOLATE_ASYNC_MIGRATE)) {
+ /* All the caller can do on PageWriteback is block */
+ if (PageWriteback(page))
+ return ret;
+
+ if (PageDirty(page)) {
+ struct address_space *mapping;
+
+ /* ISOLATE_CLEAN means only clean pages */
+ if (mode & ISOLATE_CLEAN)
+ return ret;
+
+ /*
+ * Only pages without mappings or that have a
+ * ->migratepage callback are possible to migrate
+ * without blocking
+ */
+ mapping = page_mapping(page);
+ if (mapping && !mapping->a_ops->migratepage)
+ return ret;
+ }
+ }
if ((mode & ISOLATE_UNMAPPED) && page_mapped(page))
return ret;
--
1.7.3.4
--
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