[PATCH] Kill PF_SYNCWRITE flag

A process flag to indicate whether we are doing sync io is incredibly
ugly. It also causes performance problems when one does a lot of async
io and then proceeds to sync it. Part of the io will go out as async,
and the other part as sync. This causes a disconnect between the
previously submitted io and the synced io. For io schedulers such as CFQ,
this will cause us lost merges and suboptimal behaviour in scheduling.

Remove PF_SYNCWRITE completely from the fsync/msync paths, and let
the O_DIRECT path just directly indicate that the writes are sync
by using WRITE_SYNC instead.

Signed-off-by: Jens Axboe <axboe@suse.de>

3 files changed, 5 insertions, 4 deletions

diff --git a/block/as-iosched.c b/block/as-iosched.c
index 9b13d72ffefa..56c99fa037df 100644
--- a/block/as-iosched.c
+++ b/block/as-iosched.c
@@ -1339,7 +1339,7 @@ static void as_add_request(request_queue_t *q, struct request *rq)
         arq->state = AS_RQ_NEW;
 
         if (rq_data_dir(arq->request) == READ
-                        || current->flags&PF_SYNCWRITE)
+                        || (arq->request->flags & REQ_RW_SYNC))
                 arq->is_sync = 1;
         else
                 arq->is_sync = 0;
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index c88f161d3fb3..4c4e9cc3ae26 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -277,8 +277,6 @@ static struct cfq_queue *cfq_find_cfq_hash(struct cfq_data *, unsigned int, unsi
 static void cfq_dispatch_insert(request_queue_t *, struct cfq_rq *);
 static struct cfq_queue *cfq_get_queue(struct cfq_data *cfqd, unsigned int key, struct task_struct *tsk, gfp_t gfp_mask);
 
-#define process_sync(tsk)       ((tsk)->flags & PF_SYNCWRITE)
-
 /*
  * lots of deadline iosched dupes, can be abstracted later...
  */
@@ -334,7 +332,7 @@ static int cfq_queue_empty(request_queue_t *q)
 
 static inline pid_t cfq_queue_pid(struct task_struct *task, int rw)
 {
-        if (rw == READ || process_sync(task))
+        if (rw == READ || rw == WRITE_SYNC)
                 return task->pid;
 
         return CFQ_KEY_ASYNC;
diff --git a/block/ll_rw_blk.c b/block/ll_rw_blk.c
index 17c42ddd31db..2270bb451385 100644
--- a/block/ll_rw_blk.c
+++ b/block/ll_rw_blk.c
@@ -2827,6 +2827,9 @@ static void init_request_from_bio(struct request *req, struct bio *bio)
         if (unlikely(bio_barrier(bio)))
                 req->flags |= (REQ_HARDBARRIER | REQ_NOMERGE);
 
+        if (bio_sync(bio))
+                req->flags |= REQ_RW_SYNC;
+
         req->errors = 0;
         req->hard_sector = req->sector = bio->bi_sector;
         req->hard_nr_sectors = req->nr_sectors = bio_sectors(bio);