linux-ext4 - Re: [PATCH] ext4: add cond_resched() to ext4_mb_init

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Date:   Thu, 18 Apr 2019 13:53:26 +0200
From:   Jan Kara <jack@...e.cz>
To:     Khazhismel Kumykov <khazhy@...gle.com>
Cc:     tytso@....edu, adilger.kernel@...ger.ca,
        linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ext4: add cond_resched() to ext4_mb_init_backend()

On Mon 15-04-19 19:59:34, Khazhismel Kumykov wrote:
> on non-preempt kernels for filesystems with large number of groups we
> may take a long time (>50 ticks) initializing all the groups.
> 
> Signed-off-by: Khazhismel Kumykov <khazhy@...gle.com>

Thanks for the patch. I'm not opposed to this but I'm just wondering: Has
this caused any real issues to you? Or how have you come across this
particular loop? Because I'd think we have more similar loops in ext4
codebase...

								Honza

> ---
>  fs/ext4/mballoc.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 8ef5f12bbee2..c89f497ccf50 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -2490,6 +2490,7 @@ static int ext4_mb_init_backend(struct super_block *sb)
>  	sbi->s_buddy_cache->i_ino = EXT4_BAD_INO;
>  	EXT4_I(sbi->s_buddy_cache)->i_disksize = 0;
>  	for (i = 0; i < ngroups; i++) {
> +		cond_resched();
>  		desc = ext4_get_group_desc(sb, i, NULL);
>  		if (desc == NULL) {
>  			ext4_msg(sb, KERN_ERR, "can't read descriptor %u", i);
> -- 
> 2.21.0.392.gf8f6787159e-goog
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR