linux-ext4 - [PATCH 27/27] direct-io: remove random prefetches

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Date:   Wed,  6 Apr 2022 08:05:16 +0200
From:   Christoph Hellwig <hch@....de>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     dm-devel@...hat.com, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-um@...ts.infradead.org,
        linux-block@...r.kernel.org, drbd-dev@...ts.linbit.com,
        nbd@...er.debian.org, ceph-devel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        xen-devel@...ts.xenproject.org, linux-bcache@...r.kernel.org,
        linux-raid@...r.kernel.org, linux-mmc@...r.kernel.org,
        linux-mtd@...ts.infradead.org, linux-nvme@...ts.infradead.org,
        linux-s390@...r.kernel.org, linux-scsi@...r.kernel.org,
        target-devel@...r.kernel.org, linux-btrfs@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net,
        cluster-devel@...hat.com, jfs-discussion@...ts.sourceforge.net,
        linux-nilfs@...r.kernel.org, ntfs3@...ts.linux.dev,
        ocfs2-devel@....oracle.com, linux-mm@...ck.org
Subject: [PATCH 27/27] direct-io: remove random prefetches

Randomly poking into block device internals for manual prefetches isn't
exactly a very maintainable thing to do.  And none of the performance
criticil direct I/O implementations still use this library function
anyway, so just drop it.

Signed-off-by: Christoph Hellwig <hch@....de>
---
 fs/direct-io.c | 32 ++++----------------------------
 1 file changed, 4 insertions(+), 28 deletions(-)

diff --git a/fs/direct-io.c b/fs/direct-io.c
index aef06e607b405..840752006f601 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -1115,11 +1115,10 @@ static inline int drop_refcount(struct dio *dio)
  * individual fields and will generate much worse code. This is important
  * for the whole file.
  */
-static inline ssize_t
-do_blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
-		      struct block_device *bdev, struct iov_iter *iter,
-		      get_block_t get_block, dio_iodone_t end_io,
-		      dio_submit_t submit_io, int flags)
+ssize_t __blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
+		struct block_device *bdev, struct iov_iter *iter,
+		get_block_t get_block, dio_iodone_t end_io,
+		dio_submit_t submit_io, int flags)
 {
 	unsigned i_blkbits = READ_ONCE(inode->i_blkbits);
 	unsigned blkbits = i_blkbits;
@@ -1334,29 +1333,6 @@ do_blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
 	kmem_cache_free(dio_cache, dio);
 	return retval;
 }
-
-ssize_t __blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
-			     struct block_device *bdev, struct iov_iter *iter,
-			     get_block_t get_block,
-			     dio_iodone_t end_io, dio_submit_t submit_io,
-			     int flags)
-{
-	/*
-	 * The block device state is needed in the end to finally
-	 * submit everything.  Since it's likely to be cache cold
-	 * prefetch it here as first thing to hide some of the
-	 * latency.
-	 *
-	 * Attempt to prefetch the pieces we likely need later.
-	 */
-	prefetch(&bdev->bd_disk->part_tbl);
-	prefetch(bdev->bd_disk->queue);
-	prefetch((char *)bdev->bd_disk->queue + SMP_CACHE_BYTES);
-
-	return do_blockdev_direct_IO(iocb, inode, bdev, iter, get_block,
-				     end_io, submit_io, flags);
-}
-
 EXPORT_SYMBOL(__blockdev_direct_IO);
 
 static __init int dio_init(void)
-- 
2.30.2