[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>

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;