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Date:   Wed, 24 Apr 2019 08:21:36 +0200
From:   Andreas Dilger <adilger@...ger.ca>
To:     Khazhismel Kumykov <khazhy@...gle.com>
Cc:     Theodore Ts'o <tytso@....edu>,
        linux-ext4 <linux-ext4@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Jan Kara <jack@...e.cz>
Subject: Re: [PATCH v2] ext4: cond_resched in work-heavy group loops

On Apr 23, 2019, at 11:13 PM, Khazhismel Kumykov <khazhy@...gle.com> wrote:
> 
> These functions may take a long time looping over many groups, which
> may cause issues for non-preempt kernels.
> ext4_mb_init_backend()
> ext4_setup_system_zone()
> ext4_mb_release()
> 
> Signed-off-by: Khazhismel Kumykov <khazhy@...gle.com>

Reviewed-by: Andreas Dilger <adilger@...ger.ca>

> ---
> v2:
> - a few other places that in testing showed to be slow
> 
> fs/ext4/block_validity.c | 1 +
> fs/ext4/mballoc.c        | 2 ++
> 2 files changed, 3 insertions(+)
> 
> diff --git a/fs/ext4/block_validity.c b/fs/ext4/block_validity.c
> index 913061c0de1b..16134469ea3c 100644
> --- a/fs/ext4/block_validity.c
> +++ b/fs/ext4/block_validity.c
> @@ -155,6 +155,7 @@ int ext4_setup_system_zone(struct super_block *sb)
> 		return 0;
> 
> 	for (i=0; i < ngroups; i++) {
> +		cond_resched();
> 		if (ext4_bg_has_super(sb, i) &&
> 		    ((i < 5) || ((i % flex_size) == 0)))
> 			add_system_zone(sbi, ext4_group_first_block_no(sb, i),
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 8ef5f12bbee2..99ba720dbb7a 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);
> @@ -2705,6 +2706,7 @@ int ext4_mb_release(struct super_block *sb)
> 
> 	if (sbi->s_group_info) {
> 		for (i = 0; i < ngroups; i++) {
> +			cond_resched();
> 			grinfo = ext4_get_group_info(sb, i);
> #ifdef DOUBLE_CHECK
> 			kfree(grinfo->bb_bitmap);
> --
> 2.21.0.593.g511ec345e18-goog
> 


Cheers, Andreas






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