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Subject: [PATCH 2/9] Remove bdi_congested() and wb_congested() and related
 functions
From:   NeilBrown <neilb@suse.de>
To:     Andrew Morton <akpm@linux-foundation.org>,
        Jaegeuk Kim <jaegeuk@kernel.org>, Chao Yu <chao@kernel.org>,
        Jeff Layton <jlayton@kernel.org>,
        Ilya Dryomov <idryomov@gmail.com>,
        Miklos Szeredi <miklos@szeredi.hu>,
        Trond Myklebust <trond.myklebust@hammerspace.com>,
        Anna Schumaker <anna.schumaker@netapp.com>,
        Ryusuke Konishi <konishi.ryusuke@gmail.com>,
        "Darrick J. Wong" <djwong@kernel.org>,
        Philipp Reisner <philipp.reisner@linbit.com>,
        Lars Ellenberg <lars.ellenberg@linbit.com>,
        Paolo Valente <paolo.valente@linaro.org>,
        Jens Axboe <axboe@kernel.dk>
Cc:     linux-mm@kvack.org, linux-nilfs@vger.kernel.org,
        linux-nfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net, linux-ext4@vger.kernel.org,
        ceph-devel@vger.kernel.org, drbd-dev@lists.linbit.com,
        linux-kernel@vger.kernel.org, linux-block@vger.kernel.org
Date:   Thu, 27 Jan 2022 13:46:29 +1100
Message-ID: <164325158955.29787.4769373293473421057.stgit@noble.brown>
In-Reply-To: <164325106958.29787.4865219843242892726.stgit@noble.brown>
References: <164325106958.29787.4865219843242892726.stgit@noble.brown>
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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 <neilb@suse.de>
---
 drivers/block/drbd/drbd_int.h |    3 ---
 drivers/block/drbd/drbd_req.c |    3 +--
 fs/ext2/ialloc.c              |    2 --
 fs/nilfs2/segbuf.c            |   11 -----------
 fs/xfs/xfs_buf.c              |    3 ---
 include/linux/backing-dev.h   |   26 --------------------------
 mm/vmscan.c                   |    4 +---
 7 files changed, 2 insertions(+), 50 deletions(-)

diff --git a/drivers/block/drbd/drbd_int.h b/drivers/block/drbd/drbd_int.h
index f27d5b0f9a0b..f804b1bfb3e6 100644
--- a/drivers/block/drbd/drbd_int.h
+++ b/drivers/block/drbd/drbd_int.h
@@ -638,9 +638,6 @@ enum {
 	STATE_SENT,		/* Do not change state/UUIDs while this is set */
 	CALLBACK_PENDING,	/* Whether we have a call_usermodehelper(, UMH_WAIT_PROC)
 				 * pending, from drbd worker context.
-				 * If set, bdi_write_congested() returns true,
-				 * so shrink_page_list() would not recurse into,
-				 * and potentially deadlock on, this drbd worker.
 				 */
 	DISCONNECT_SENT,
 
diff --git a/drivers/block/drbd/drbd_req.c b/drivers/block/drbd/drbd_req.c
index 3235532ae077..2e5fb7e442e3 100644
--- a/drivers/block/drbd/drbd_req.c
+++ b/drivers/block/drbd/drbd_req.c
@@ -909,8 +909,7 @@ static bool remote_due_to_read_balancing(struct drbd_device *device, sector_t se
 
 	switch (rbm) {
 	case RB_CONGESTED_REMOTE:
-		return bdi_read_congested(
-			device->ldev->backing_bdev->bd_disk->bdi);
+		return 0;
 	case RB_LEAST_PENDING:
 		return atomic_read(&device->local_cnt) >
 			atomic_read(&device->ap_pending_cnt) + atomic_read(&device->rs_pending_cnt);
diff --git a/fs/ext2/ialloc.c b/fs/ext2/ialloc.c
index df14e750e9fe..d632764da240 100644
--- a/fs/ext2/ialloc.c
+++ b/fs/ext2/ialloc.c
@@ -173,8 +173,6 @@ static void ext2_preread_inode(struct inode *inode)
 	struct backing_dev_info *bdi;
 
 	bdi = inode_to_bdi(inode);
-	if (bdi_rw_congested(bdi))
-		return;
 
 	block_group = (inode->i_ino - 1) / EXT2_INODES_PER_GROUP(inode->i_sb);
 	gdp = ext2_get_group_desc(inode->i_sb, block_group, NULL);
diff --git a/fs/nilfs2/segbuf.c b/fs/nilfs2/segbuf.c
index 43287b0d3e9b..d1ebc9da7130 100644
--- a/fs/nilfs2/segbuf.c
+++ b/fs/nilfs2/segbuf.c
@@ -343,17 +343,6 @@ static int nilfs_segbuf_submit_bio(struct nilfs_segment_buffer *segbuf,
 	struct bio *bio = wi->bio;
 	int err;
 
-	if (segbuf->sb_nbio > 0 &&
-	    bdi_write_congested(segbuf->sb_super->s_bdi)) {
-		wait_for_completion(&segbuf->sb_bio_event);
-		segbuf->sb_nbio--;
-		if (unlikely(atomic_read(&segbuf->sb_err))) {
-			bio_put(bio);
-			err = -EIO;
-			goto failed;
-		}
-	}
-
 	bio->bi_end_io = nilfs_end_bio_write;
 	bio->bi_private = segbuf;
 	bio_set_op_attrs(bio, mode, mode_flags);
diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index b45e0d50a405..b7ebcfe6b8d3 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;
-
 	xfs_buf_read_map(target, map, nmaps,
 		     XBF_TRYLOCK | XBF_ASYNC | XBF_READ_AHEAD, &bp, ops,
 		     __this_address);
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index 860b675c2929..2d764566280c 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -135,11 +135,6 @@ static inline bool writeback_in_progress(struct bdi_writeback *wb)
 
 struct backing_dev_info *inode_to_bdi(struct inode *inode);
 
-static inline int wb_congested(struct bdi_writeback *wb, int cong_bits)
-{
-	return wb->congested & cong_bits;
-}
-
 long congestion_wait(int sync, long timeout);
 
 static inline bool mapping_can_writeback(struct address_space *mapping)
@@ -391,27 +386,6 @@ static inline void wb_blkcg_offline(struct blkcg *blkcg)
 
 #endif	/* CONFIG_CGROUP_WRITEBACK */
 
-static inline int bdi_congested(struct backing_dev_info *bdi, int cong_bits)
-{
-	return wb_congested(&bdi->wb, cong_bits);
-}
-
-static inline int bdi_read_congested(struct backing_dev_info *bdi)
-{
-	return bdi_congested(bdi, 1 << WB_sync_congested);
-}
-
-static inline int bdi_write_congested(struct backing_dev_info *bdi)
-{
-	return bdi_congested(bdi, 1 << WB_async_congested);
-}
-
-static inline int bdi_rw_congested(struct backing_dev_info *bdi)
-{
-	return bdi_congested(bdi, (1 << WB_sync_congested) |
-				  (1 << WB_async_congested));
-}
-
 const char *bdi_dev_name(struct backing_dev_info *bdi);
 
 #endif	/* _LINUX_BACKING_DEV_H */
diff --git a/mm/vmscan.c b/mm/vmscan.c
index ce8492939bd3..0b930556c4f2 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2362,9 +2362,7 @@ static unsigned int move_pages_to_lru(struct lruvec *lruvec,
  */
 static int current_may_throttle(void)
 {
-	return !(current->flags & PF_LOCAL_THROTTLE) ||
-		current->backing_dev_info == NULL ||
-		bdi_write_congested(current->backing_dev_info);
+	return !(current->flags & PF_LOCAL_THROTTLE);
 }
 
 /*