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Subject: [PATCH 4/6] EXT4: remove congestion_wait from ext4_bio_write_page,
 and simplify
From:   NeilBrown <neilb@suse.de>
To:     Andrew Morton <akpm@linux-foundation.org>,
        Theodore Ts'o <tytso@mit.edu>,
        Andreas Dilger <adilger.kernel@dilger.ca>,
        "Darrick J. Wong" <djwong@kernel.org>,
        Matthew Wilcox <willy@infradead.org>,
        Mel Gorman <mgorman@suse.de>, Michal Hocko <mhocko@suse.com>,
        ". Dave Chinner" <david@fromorbit.com>,
        Jonathan Corbet <corbet@lwn.net>
Cc:     linux-xfs@vger.kernel.org, linux-ext4@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        linux-doc@vger.kernel.org
Date:   Fri, 17 Sep 2021 12:56:57 +1000
Message-ID: <163184741781.29351.8660877195340279243.stgit@noble.brown>
In-Reply-To: <163184698512.29351.4735492251524335974.stgit@noble.brown>
References: <163184698512.29351.4735492251524335974.stgit@noble.brown>
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congestion_wait() is indistinguishable from
schedule_timeout_uninterruptible().  It is best avoided and should be
deprecated.

It is not needed in ext4_bio_write_page().  There are two cases.
If there are no ->io_bio yet, then it is appropriate to use __GFP_NOFAIL
which does the waiting in a better place.  The code already uses this
flag on the second attempt.  This patch changes to it always use that
flag for this case.

If there *are* ->io_bio (in which case the allocation was non-blocking)
we submit the io and return the first case.  No waiting is needed in
this case.

So remove the congestion_wait() call, and simplify the code so that the
two cases are somewhat clearer.

Remove the "if (io->io_bio)" before calling ext4_io_submit() as that
test is performed internally by that function.

Signed-off-by: NeilBrown <neilb@suse.de>
---
 fs/ext4/page-io.c |   13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
index f038d578d8d8..3b6ece0d3ad6 100644
--- a/fs/ext4/page-io.c
+++ b/fs/ext4/page-io.c
@@ -506,7 +506,7 @@ int ext4_bio_write_page(struct ext4_io_submit *io,
 	 * can't happen in the common case of blocksize == PAGE_SIZE.
 	 */
 	if (fscrypt_inode_uses_fs_layer_crypto(inode) && nr_to_submit) {
-		gfp_t gfp_flags = GFP_NOFS;
+		gfp_t gfp_flags;
 		unsigned int enc_bytes = round_up(len, i_blocksize(inode));
 
 		/*
@@ -514,21 +514,18 @@ int ext4_bio_write_page(struct ext4_io_submit *io,
 		 * a waiting mask (i.e. request guaranteed allocation) on the
 		 * first page of the bio.  Otherwise it can deadlock.
 		 */
+	retry_encrypt:
 		if (io->io_bio)
 			gfp_flags = GFP_NOWAIT | __GFP_NOWARN;
-	retry_encrypt:
+		else
+			gfp_flags = GFP_NOFS | __GFP_NOFAIL;
 		bounce_page = fscrypt_encrypt_pagecache_blocks(page, enc_bytes,
 							       0, gfp_flags);
 		if (IS_ERR(bounce_page)) {
 			ret = PTR_ERR(bounce_page);
 			if (ret == -ENOMEM &&
 			    (io->io_bio || wbc->sync_mode == WB_SYNC_ALL)) {
-				gfp_flags = GFP_NOFS;
-				if (io->io_bio)
-					ext4_io_submit(io);
-				else
-					gfp_flags |= __GFP_NOFAIL;
-				congestion_wait(BLK_RW_ASYNC, HZ/50);
+				ext4_io_submit(io);
 				goto retry_encrypt;
 			}