linux-kernel - [PATCH v2 08/12] ext4: Don't skip prefetching BLOCK

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Message-Id: <dc3130b8daf45ffe63d8a3c1edcf00eb8ba70e1f.1685449706.git.ojaswin@linux.ibm.com>
Date:   Tue, 30 May 2023 18:03:46 +0530
From:   Ojaswin Mujoo <ojaswin@...ux.ibm.com>
To:     linux-ext4@...r.kernel.org, "Theodore Ts'o" <tytso@....edu>
Cc:     Ritesh Harjani <riteshh@...ux.ibm.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jan Kara <jack@...e.cz>,
        Kemeng Shi <shikemeng@...weicloud.com>,
        Ritesh Harjani <ritesh.list@...il.com>
Subject: [PATCH v2 08/12] ext4: Don't skip prefetching BLOCK_UNINIT groups

Currently, ext4_mb_prefetch() and ext4_mb_prefetch_fini() skip
BLOCK_UNINIT groups since fetching their bitmaps doesn't need disk IO.
As a consequence, we end not initializing the buddy structures and CR0/1
lists for these BGs, even though it can be done without any disk IO
overhead. Hence, don't skip such BGs during prefetch and prefetch_fini.

This improves the accuracy of CR0/1 allocation as earlier, we could have
essentially empty BLOCK_UNINIT groups being ignored by CR0/1 due to their buddy
not being initialized, leading to slower CR2 allocations. With this patch CR0/1
will be able to discover these groups as well, thus improving performance.

Signed-off-by: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@...il.com>
Reviewed-by: Jan Kara <jack@...e.cz>
---
 fs/ext4/mballoc.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index c86565606359..79455c7e645b 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2590,9 +2590,7 @@ ext4_group_t ext4_mb_prefetch(struct super_block *sb, ext4_group_t group,
 		 */
 		if (gdp && grp && !EXT4_MB_GRP_TEST_AND_SET_READ(grp) &&
 		    EXT4_MB_GRP_NEED_INIT(grp) &&
-		    ext4_free_group_clusters(sb, gdp) > 0 &&
-		    !(ext4_has_group_desc_csum(sb) &&
-		      (gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)))) {
+		    ext4_free_group_clusters(sb, gdp) > 0 ) {
 			bh = ext4_read_block_bitmap_nowait(sb, group, true);
 			if (bh && !IS_ERR(bh)) {
 				if (!buffer_uptodate(bh) && cnt)
@@ -2633,9 +2631,7 @@ void ext4_mb_prefetch_fini(struct super_block *sb, ext4_group_t group,
 		grp = ext4_get_group_info(sb, group);
 
 		if (grp && gdp && EXT4_MB_GRP_NEED_INIT(grp) &&
-		    ext4_free_group_clusters(sb, gdp) > 0 &&
-		    !(ext4_has_group_desc_csum(sb) &&
-		      (gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)))) {
+		    ext4_free_group_clusters(sb, gdp) > 0) {
 			if (ext4_mb_init_group(sb, group, GFP_NOFS))
 				break;
 		}
-- 
2.31.1