[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, 0 insertions, 3 deletions

diff --git a/mm/msync.c b/mm/msync.c
index bc6c953..d083544 100644
--- a/mm/msync.c
+++ b/mm/msync.c
@@ -170,8 +170,6 @@ asmlinkage long sys_msync(unsigned long start, size_t len, int flags)
 	 * just ignore them, but return -ENOMEM at the end.
 	 */
 	down_read(&current->mm->mmap_sem);
-	if (flags & MS_SYNC)
-		current->flags |= PF_SYNCWRITE;
 	vma = find_vma(current->mm, start);
 	if (!vma) {
 		error = -ENOMEM;
@@ -228,7 +226,6 @@ asmlinkage long sys_msync(unsigned long start, size_t len, int flags)
 		}
 	} while (vma && !done);
 out_unlock:
-	current->flags &= ~PF_SYNCWRITE;
 	up_read(&current->mm->mmap_sem);
 out:
 	return error;