[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, 3 insertions, 0 deletions

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);