linux-kernel - [PATCH 5.15 148/148] ext4: use locality group preallocation for small closed files

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Message-Id: <20220926100801.796536949@linuxfoundation.org>
Date:   Mon, 26 Sep 2022 12:13:02 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, stable@...nel.org,
        Ojaswin Mujoo <ojaswin@...ux.ibm.com>,
        "Ritesh Harjani (IBM)" <ritesh.list@...il.com>,
        Jan Kara <jack@...e.cz>, Theodore Tso <tytso@....edu>,
        Stefan Wahren <stefan.wahren@...e.com>
Subject: [PATCH 5.15 148/148] ext4: use locality group preallocation for small closed files

From: Jan Kara <jack@...e.cz>

commit a9f2a2931d0e197ab28c6007966053fdababd53f upstream.

Curently we don't use any preallocation when a file is already closed
when allocating blocks (from writeback code when converting delayed
allocation). However for small files, using locality group preallocation
is actually desirable as that is not specific to a particular file.
Rather it is a method to pack small files together to reduce
fragmentation and for that the fact the file is closed is actually even
stronger hint the file would benefit from packing. So change the logic
to allow locality group preallocation in this case.

Fixes: 196e402adf2e ("ext4: improve cr 0 / cr 1 group scanning")
CC: stable@...nel.org
Reported-and-tested-by: Stefan Wahren <stefan.wahren@...e.com>
Tested-by: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@...il.com>
Signed-off-by: Jan Kara <jack@...e.cz>
Link: https://lore.kernel.org/all/0d81a7c2-46b7-6010-62a4-3e6cfc1628d6@i2se.com/
Link: https://lore.kernel.org/r/20220908092136.11770-4-jack@suse.cz
Signed-off-by: Theodore Ts'o <tytso@....edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 fs/ext4/mballoc.c |   27 +++++++++++++++------------
 1 file changed, 15 insertions(+), 12 deletions(-)

--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -5169,6 +5169,7 @@ static void ext4_mb_group_or_file(struct
 	struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
 	int bsbits = ac->ac_sb->s_blocksize_bits;
 	loff_t size, isize;
+	bool inode_pa_eligible, group_pa_eligible;
 
 	if (!(ac->ac_flags & EXT4_MB_HINT_DATA))
 		return;
@@ -5176,25 +5177,27 @@ static void ext4_mb_group_or_file(struct
 	if (unlikely(ac->ac_flags & EXT4_MB_HINT_GOAL_ONLY))
 		return;
 
+	group_pa_eligible = sbi->s_mb_group_prealloc > 0;
+	inode_pa_eligible = true;
 	size = ac->ac_o_ex.fe_logical + EXT4_C2B(sbi, ac->ac_o_ex.fe_len);
 	isize = (i_size_read(ac->ac_inode) + ac->ac_sb->s_blocksize - 1)
 		>> bsbits;
 
+	/* No point in using inode preallocation for closed files */
 	if ((size == isize) && !ext4_fs_is_busy(sbi) &&
-	    !inode_is_open_for_write(ac->ac_inode)) {
-		ac->ac_flags |= EXT4_MB_HINT_NOPREALLOC;
-		return;
-	}
-
-	if (sbi->s_mb_group_prealloc <= 0) {
-		ac->ac_flags |= EXT4_MB_STREAM_ALLOC;
-		return;
-	}
+	    !inode_is_open_for_write(ac->ac_inode))
+		inode_pa_eligible = false;
 
-	/* don't use group allocation for large files */
 	size = max(size, isize);
-	if (size > sbi->s_mb_stream_request) {
-		ac->ac_flags |= EXT4_MB_STREAM_ALLOC;
+	/* Don't use group allocation for large files */
+	if (size > sbi->s_mb_stream_request)
+		group_pa_eligible = false;
+
+	if (!group_pa_eligible) {
+		if (inode_pa_eligible)
+			ac->ac_flags |= EXT4_MB_STREAM_ALLOC;
+		else
+			ac->ac_flags |= EXT4_MB_HINT_NOPREALLOC;
 		return;
 	}