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Date: Thu, 13 Aug 2020 20:48:50 +0530
From: Ritesh Harjani <riteshh@...ux.ibm.com>
To: brookxu <brookxu.cn@...il.com>, adilger.kernel@...ger.ca,
tytso@....edu, linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: put grp related checks into ext4_mb_good_group()
On 8/7/20 7:31 PM, brookxu wrote:
> We will make these judgments in ext4_mb_good_group(), maybe there
> is no need to repeat judgments here.
>
> Signed-off-by: Chunguang Xu <brookxu@...cent.com>
Nack. This could essentially cause performance issues.
But then maybe we should add a comment saying these extra checks are
intentionally done here without explicit ext4_lock_group() for
performance optimizations.
-ritesh
> ---
> fs/ext4/mballoc.c | 16 ++--------------
> 1 file changed, 2 insertions(+), 14 deletions(-)
>
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 4304113..84871f7 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -2178,21 +2178,8 @@ static int ext4_mb_good_group_nolock(struct ext4_allocation_context *ac,
> struct ext4_group_info *grp = ext4_get_group_info(ac->ac_sb, group);
> struct super_block *sb = ac->ac_sb;
> bool should_lock = ac->ac_flags & EXT4_MB_STRICT_CHECK;
> - ext4_grpblk_t free;
> int ret = 0;
>
> - if (should_lock)
> - ext4_lock_group(sb, group);
> - free = grp->bb_free;
> - if (free == 0)
> - goto out;
> - if (cr <= 2 && free < ac->ac_g_ex.fe_len)
> - goto out;
> - if (unlikely(EXT4_MB_GRP_BBITMAP_CORRUPT(grp)))
> - goto out;
> - if (should_lock)
> - ext4_unlock_group(sb, group);
> -
> /* We only do this if the grp has never been initialized */
> if (unlikely(EXT4_MB_GRP_NEED_INIT(grp))) {
> ret = ext4_mb_init_group(ac->ac_sb, group, GFP_NOFS);
> @@ -2202,8 +2189,9 @@ static int ext4_mb_good_group_nolock(struct ext4_allocation_context *ac,
>
> if (should_lock)
> ext4_lock_group(sb, group);
> +
> ret = ext4_mb_good_group(ac, group, cr);
> -out:
> +
> if (should_lock)
> ext4_unlock_group(sb, group);
> return ret;
>
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