[PATCH 1/2] staging: zram: minimize `slot_free_lock' usage (v3)

[Sergey Senozhatsky <sergey.senozhatsky@gmail.com>]

Calling handle_pending_slot_free() for every RW operation may
cause unneccessary slot_free_lock locking, because most likely
process will see NULL slot_free_rq. handle_pending_slot_free()
only when current detects that slot_free_rq is not NULL.

v3: do not acquire zram lock in zram_slot_free().
v2: protect handle_pending_slot_free() with zram rw_lock.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>

---

 drivers/staging/zram/zram_drv.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
index 91d94b5..a8261b4 100644
--- a/drivers/staging/zram/zram_drv.c
+++ b/drivers/staging/zram/zram_drv.c
@@ -517,6 +517,7 @@ static void handle_pending_slot_free(struct zram *zram)
 {
 	struct zram_slot_free *free_rq;
 
+	down_write(&zram->lock);
 	spin_lock(&zram->slot_free_lock);
 	while (zram->slot_free_rq) {
 		free_rq = zram->slot_free_rq;
@@ -525,6 +526,7 @@ static void handle_pending_slot_free(struct zram *zram)
 		kfree(free_rq);
 	}
 	spin_unlock(&zram->slot_free_lock);
+	up_write(&zram->lock);
 }
 
 static int zram_bvec_rw(struct zram *zram, struct bio_vec *bvec, u32 index,
@@ -532,14 +534,15 @@ static int zram_bvec_rw(struct zram *zram, struct bio_vec *bvec, u32 index,
 {
 	int ret;
 
+	if (zram->slot_free_rq)
+		handle_pending_slot_free(zram);
+
 	if (rw == READ) {
 		down_read(&zram->lock);
-		handle_pending_slot_free(zram);
 		ret = zram_bvec_read(zram, bvec, index, offset, bio);
 		up_read(&zram->lock);
 	} else {
 		down_write(&zram->lock);
-		handle_pending_slot_free(zram);
 		ret = zram_bvec_write(zram, bvec, index, offset);
 		up_write(&zram->lock);
 	}
@@ -753,9 +756,7 @@ static void zram_slot_free(struct work_struct *work)
 	struct zram *zram;
 
 	zram = container_of(work, struct zram, free_work);
-	down_write(&zram->lock);
 	handle_pending_slot_free(zram);
-	up_write(&zram->lock);
 }
 
 static void add_slot_free(struct zram *zram, struct zram_slot_free *free_rq)