[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>

1 files changed, 1 insertions, 3 deletions

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;