"NeilBrown" <neilb@xxxxxxx> writes: > On Sun, 21 Nov 2021, OGAWA Hirofumi wrote: >> "NeilBrown" <neilb@xxxxxxx> writes: >> >> > congestion_wait() in this context is just a sleep - block devices do not >> > in general support congestion signalling any more. >> > >> > The goal here is to wait for any recently written data to get to >> > storage. This can be achieved using blkdev_issue_flush(). >> >> Purpose of flush option should be for making umount faster, not data >> integrity. (but current flush implement is strange at several places, IMO) > > I don't think that is true. I believe the purpose of the flush option > is to write out data as soon as a file is closed, so that if the media > is removed without first unmounting, the data is more likely to be safe. > That is why the commit which introduce it: > Commit ae78bf9c4f5f ("[PATCH] add -o flush for fat") > particularly mentions "removable media". Right. This was to make the removable device usage better (but sync option is too slow). e.g. # cp -a /foo/source /mnt/fatfs # umount <don't too slow> or <do other thing, and forget umount> >> So, I don't think the issue_flush is not proper for it (flush is very >> slow on some usb thumb), and rather I think it is better off to just >> remove the congestion_wait(). > > We already call blkdev_issue_flush() on fsync. With my patch, a simple > close() effective becomes an fsync() and a close(). I think that is > completely consistent with the purpose of "-o flush". It makes much slower above "cp -a" part. So I think it is overkill. -- OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>