linux-ext4 - [PATCH v3 04/20] ext4: correct calculation of s_mb

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Date:   Sat,  4 Mar 2023 01:21:04 +0800
From:   Kemeng Shi <shikemeng@...weicloud.com>
To:     tytso@....edu, adilger.kernel@...ger.ca, ojaswin@...ux.ibm.com,
        ritesh.list@...il.com
Cc:     linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
        shikemeng@...weicloud.com
Subject: [PATCH v3 04/20] ext4: correct calculation of s_mb_preallocated

We will add pa_free to s_mb_preallocated when new ext4_prealloc_space is
created. In ext4_mb_new_inode_pa, we will call ext4_mb_use_inode_pa
before adding pa_free to s_mb_preallocated. However, ext4_mb_use_inode_pa
will consume pa_free for block allocation which triggerred the creation
of ext4_prealloc_space. Add pa_free to s_mb_preallocated before
ext4_mb_use_inode_pa to correct calculation of s_mb_preallocated.
There is no such problem in ext4_mb_new_group_pa as pa_free of group pa
is consumed in ext4_mb_release_context instead of ext4_mb_use_group_pa.

Signed-off-by: Kemeng Shi <shikemeng@...weicloud.com>
Reviewed-by: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
---
 fs/ext4/mballoc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index d1c5b6ea57da..d7ea3c2014ff 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -4670,8 +4670,8 @@ ext4_mb_new_inode_pa(struct ext4_allocation_context *ac)
 		 pa->pa_len, pa->pa_lstart);
 	trace_ext4_mb_new_inode_pa(ac, pa);

-	ext4_mb_use_inode_pa(ac, pa);
 	atomic_add(pa->pa_free, &sbi->s_mb_preallocated);
+	ext4_mb_use_inode_pa(ac, pa);

 	ei = EXT4_I(ac->ac_inode);
 	grp = ext4_get_group_info(sb, ac->ac_b_ex.fe_group);
-- 
2.30.0