[PATCH 14/23] workingset: Use xas_store_noinit() to clear shadow entry

[Jan Kara]

Shadow entries have no marks. Use xas_store_noinit() to clear the entry
so avoid unneeded initialization of the xarray marks. This provides a
nice boost to truncate numbers. Sample benchmark showing time to
truncate 128 files 1GB each on machine with 64GB of RAM (so about half
of entries are shadow entries):

         AVG      STDDEV
Vanilla  4.825s   0.036
Patched  4.516s   0.014

So we can see about 6% reduction in overall truncate time.

Signed-off-by: Jan Kara <jack@xxxxxxx>
---
 mm/truncate.c   | 2 +-
 mm/workingset.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/truncate.c b/mm/truncate.c
index dd9ebc1da356..baef636564cc 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -39,7 +39,7 @@ static inline void __clear_shadow_entry(struct address_space *mapping,
 	xas_set_update(&xas, workingset_update_node);
 	if (xas_load(&xas) != entry)
 		return;
-	xas_store(&xas, NULL);
+	xas_store_noinit(&xas, NULL);
 	mapping->nrexceptional--;
 }
 
diff --git a/mm/workingset.c b/mm/workingset.c
index 474186b76ced..6a492140057f 100644
--- a/mm/workingset.c
+++ b/mm/workingset.c
@@ -537,7 +537,7 @@ static enum lru_status shadow_lru_isolate(struct list_head *item,
 	 * We could store a shadow entry here which was the minimum of the
 	 * shadow entries we were tracking ...
 	 */
-	xas_store(&xas, NULL);
+	xas_store_noinit(&xas, NULL);
 	__inc_lruvec_slab_state(node, WORKINGSET_NODERECLAIM);
 
 out_invalid:
-- 
2.16.4