Re: [PATCH 2/2] Remove bdi_congested() and wb_congested() and related functions
From: Dave Chinner <david@fromorbit.com>
Date: 2021-12-13 05:50:49
Also in:
linux-fsdevel, linux-mm, linux-xfs, lkml
On Mon, Dec 13, 2021 at 03:14:27PM +1100, NeilBrown wrote:
These functions are no longer useful as the only bdis that report congestion are in ceph, fuse, and nfs. None of those bdis can be the target of the calls in drbd, ext2, nilfs2, or xfs. Removing the test on bdi_write_contested() in current_may_throttle() could cause a small change in behaviour, but only when PF_LOCAL_THROTTLE is set. So replace the calls by 'false' and simplify the code - and remove the functions. Signed-off-by: NeilBrown <redacted>
....
quoted hunk ↗ jump to hunk
diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c index 631c5a61d89b..22f73b3e888e 100644 --- a/fs/xfs/xfs_buf.c +++ b/fs/xfs/xfs_buf.c@@ -843,9 +843,6 @@ xfs_buf_readahead_map( { struct xfs_buf *bp; - if (bdi_read_congested(target->bt_bdev->bd_disk->bdi)) - return;
Ok, but this isn't a "throttle writeback" test here - it's trying to avoid having speculative readahead blocking on a full request queue instead of just skipping the readahead IO. i.e. prevent readahead thrashing and/or adding unnecessary read load when we already have a full read queue... So what is the replacement for that? We want to skip the entire buffer lookup/setup/read overhead if we're likely to block on IO submission - is there anything we can use to do this these days? Cheers, Dave. -- Dave Chinner david@fromorbit.com