[PATCH] [RFC] mm: fs: Invalidate BH LRU during page migration

[Chris Goldsworthy <cgoldswo@codeaurora.org>]

Pages containing buffer_heads that are in the buffer_head LRU cache
will be pinned and thus cannot be migrated.  Correspondingly,
invalidate the BH LRU before a migration starts and stop any
buffer_head from being cached in the LRU, until migration has
finished.

Signed-off-by: Chris Goldsworthy <cgoldswo@codeaurora.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
---
 fs/buffer.c                 |  6 ++++++
 include/linux/buffer_head.h |  3 +++
 include/linux/migrate.h     |  2 ++
 mm/migrate.c                | 18 ++++++++++++++++++
 mm/page_alloc.c             |  3 +++
 mm/swap.c                   |  3 +++
 6 files changed, 35 insertions(+)

diff --git a/fs/buffer.c b/fs/buffer.c
index 96c7604..39ec4ec 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1289,6 +1289,8 @@ static inline void check_irqs_on(void)
 #endif
 }
 
+bool bh_migration_done = true;
+
 /*
  * Install a buffer_head into this cpu's LRU.  If not already in the LRU, it is
  * inserted at the front, and the buffer_head at the back if any is evicted.
@@ -1303,6 +1305,9 @@ static void bh_lru_install(struct buffer_head *bh)
 	check_irqs_on();
 	bh_lru_lock();
 
+	if (!bh_migration_done)
+		goto out;
+
 	b = this_cpu_ptr(&bh_lrus);
 	for (i = 0; i < BH_LRU_SIZE; i++) {
 		swap(evictee, b->bhs[i]);
@@ -1313,6 +1318,7 @@ static void bh_lru_install(struct buffer_head *bh)
 	}
 
 	get_bh(bh);
+out:
 	bh_lru_unlock();
 	brelse(evictee);
 }
diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index 6b47f94..ae4eb6d 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -193,6 +193,9 @@ void __breadahead_gfp(struct block_device *, sector_t block, unsigned int size,
 		  gfp_t gfp);
 struct buffer_head *__bread_gfp(struct block_device *,
 				sector_t block, unsigned size, gfp_t gfp);
+
+extern bool bh_migration_done;
+
 void invalidate_bh_lrus(void);
 struct buffer_head *alloc_buffer_head(gfp_t gfp_flags);
 void free_buffer_head(struct buffer_head * bh);
diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index 3a38963..9e4a2dc 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -46,6 +46,7 @@ extern int isolate_movable_page(struct page *page, isolate_mode_t mode);
 extern void putback_movable_page(struct page *page);
 
 extern void migrate_prep(void);
+extern void migrate_finish(void);
 extern void migrate_prep_local(void);
 extern void migrate_page_states(struct page *newpage, struct page *page);
 extern void migrate_page_copy(struct page *newpage, struct page *page);
@@ -67,6 +68,7 @@ static inline int isolate_movable_page(struct page *page, isolate_mode_t mode)
 	{ return -EBUSY; }
 
 static inline int migrate_prep(void) { return -ENOSYS; }
+static inline int migrate_finish(void) { return -ENOSYS; }
 static inline int migrate_prep_local(void) { return -ENOSYS; }
 
 static inline void migrate_page_states(struct page *newpage, struct page *page)
diff --git a/mm/migrate.c b/mm/migrate.c
index a69da8a..08c981d 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -64,6 +64,19 @@
  */
 void migrate_prep(void)
 {
+	bh_migration_done = false;
+
+	/*
+	 * This barrier ensures that callers of bh_lru_install() between
+	 * the barrier and the call to invalidate_bh_lrus() read
+	 *  bh_migration_done() as false.
+	 */
+	/*
+	 * TODO: Remove me? lru_add_drain_all() already has an smp_mb(),
+	 * but it would be good to ensure that the barrier isn't forgotten.
+	 */
+	smp_mb();
+
 	/*
 	 * Clear the LRU lists so pages can be isolated.
 	 * Note that pages may be moved off the LRU after we have
@@ -73,6 +86,11 @@ void migrate_prep(void)
 	lru_add_drain_all();
 }
 
+void migrate_finish(void)
+{
+	bh_migration_done = true;
+}
+
 /* Do the necessary work of migrate_prep but not if it involves other CPUs */
 void migrate_prep_local(void)
 {
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 6446778..e4cb959 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -8493,6 +8493,9 @@ static int __alloc_contig_migrate_range(struct compact_control *cc,
 		ret = migrate_pages(&cc->migratepages, alloc_migration_target,
 				NULL, (unsigned long)&mtc, cc->mode, MR_CONTIG_RANGE);
 	}
+
+	migrate_finish();
+
 	if (ret < 0) {
 		putback_movable_pages(&cc->migratepages);
 		return ret;
diff --git a/mm/swap.c b/mm/swap.c
index 31b844d..97efc49 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -36,6 +36,7 @@
 #include <linux/hugetlb.h>
 #include <linux/page_idle.h>
 #include <linux/local_lock.h>
+#include <linux/buffer_head.h>
 
 #include "internal.h"
 
@@ -759,6 +760,8 @@ void lru_add_drain_all(void)
 	if (WARN_ON(!mm_percpu_wq))
 		return;
 
+	invalidate_bh_lrus();
+
 	/*
 	 * Guarantee pagevec counter stores visible by this CPU are visible to
 	 * other CPUs before loading the current drain generation.
-- 
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