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Date:   Mon, 22 Jun 2020 11:20:47 -0600
From:   Andreas Dilger <adilger@...ger.ca>
To:     Wang Shilong <wangshilong1991@...il.com>
Cc:     Ext4 Developers List <linux-ext4@...r.kernel.org>,
        Wang Shilong <wshilong@....com>, Shuichi Ihara <sihara@....com>
Subject: Re: [PATCH v2 2/2] ext4: avoid trimming block group if only few
 blocks freed

On Jun 22, 2020, at 8:16 AM, Wang Shilong <wangshilong1991@...il.com> wrote:
> 
> From: Wang Shilong <wshilong@....com>
> 
> Now WAS_TRIMMED flag will be cleared if there are any blocks
> freed in this block group, this might be not good idea if there
> are only few blocks freed, since most of freed blocks have been
> issued discard before.
> 
> So this patch tries to introduce another counter which record
> how many blocks freed since last time trimmed, WAS_TRIMMED flag
> will be only cleared if there are enough free blocks(default 128).
> 
> Also expose a new sys interface min_freed_blocks_to_trim to tune
> default behavior.
> 
> Cc: Shuichi Ihara <sihara@....com>
> Cc: Andreas Dilger <adilger@...ger.ca>
> Cc: Wang Shilong <wangshilong1991@...il.com>
> Signed-off-by: Wang Shilong <wshilong@....com>

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

> ---
> changelog v1->v2:
> init bb_freed_last_trimmed to be zero during setup
> ---
> fs/ext4/ext4.h    |  7 +++++++
> fs/ext4/mballoc.c | 18 ++++++++++++++++--
> fs/ext4/sysfs.c   |  2 ++
> 3 files changed, 25 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 252754da2f1b..2da86d1ebe3f 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -1240,6 +1240,9 @@ extern void ext4_set_bits(void *bm, int cur, int len);
> /* Metadata checksum algorithm codes */
> #define EXT4_CRC32C_CHKSUM		1
> 
> +/* Default min freed blocks which we could clear TRIMMED flags */
> +#define DEFAULT_MIN_FREED_BLOCKS_TO_TRIM	128
> +
> /*
>  * Structure of the super block
>  */
> @@ -1533,6 +1536,9 @@ struct ext4_sb_info {
> 	/* the size of zero-out chunk */
> 	unsigned int s_extent_max_zeroout_kb;
> 
> +	/* Min freed blocks per group that we could run trim on it*/
> +	unsigned long s_min_freed_blocks_to_trim;
> +
> 	unsigned int s_log_groups_per_flex;
> 	struct flex_groups * __rcu *s_flex_groups;
> 	ext4_group_t s_flex_groups_allocated;
> @@ -3125,6 +3131,7 @@ struct ext4_group_info {
> 	struct rb_root  bb_free_root;
> 	ext4_grpblk_t	bb_first_free;	/* first free block */
> 	ext4_grpblk_t	bb_free;	/* total free blocks */
> +	ext4_grpblk_t	bb_freed_last_trimmed; /* total free blocks since last trimmed*/
> 	ext4_grpblk_t	bb_fragments;	/* nr of freespace fragments */
> 	ext4_grpblk_t	bb_largest_free_order;/* order of largest frag in BG */
> 	struct          list_head bb_prealloc_list;
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 235a316584d0..52ab9ac5be86 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -2558,6 +2558,7 @@ int ext4_mb_add_groupinfo(struct super_block *sb, ext4_group_t group,
> 	init_rwsem(&meta_group_info[i]->alloc_sem);
> 	meta_group_info[i]->bb_free_root = RB_ROOT;
> 	meta_group_info[i]->bb_largest_free_order = -1;  /* uninit */
> +	meta_group_info[i]->bb_freed_last_trimmed = 0;
> 
> 	mb_group_bb_bitmap_alloc(sb, meta_group_info[i], group);
> 	return 0;
> @@ -2763,6 +2764,8 @@ int ext4_mb_init(struct super_block *sb)
> 			sbi->s_mb_group_prealloc, sbi->s_stripe);
> 	}
> 
> +	sbi->s_min_freed_blocks_to_trim = DEFAULT_MIN_FREED_BLOCKS_TO_TRIM;
> +
> 	sbi->s_locality_groups = alloc_percpu(struct ext4_locality_group);
> 	if (sbi->s_locality_groups == NULL) {
> 		ret = -ENOMEM;
> @@ -5091,8 +5094,18 @@ void ext4_free_blocks(handle_t *handle, struct inode *inode,
> 	 * If the volume is mounted with -o discard, online discard
> 	 * is supported and the free blocks will be trimmed online.
> 	 */
> -	if (!test_opt(sb, DISCARD))
> -		EXT4_MB_GDP_CLEAR_TRIMMED(gdp);
> +	if (!test_opt(sb, DISCARD)) {
> +		e4b.bd_info->bb_freed_last_trimmed += count;
> +		/*
> +		 * Only clear the WAS_TRIMMED flag if there are
> +		 * several blocks freed, or if the group becomes
> +		 * totally 'empty'(free < num_itable_blocks + 2).
> +		 */
> +		if (e4b.bd_info->bb_freed_last_trimmed >=
> +		    sbi->s_min_freed_blocks_to_trim ||
> +		    e4b.bd_info->bb_free < (sbi->s_itb_per_group + 2))
> +			EXT4_MB_GDP_CLEAR_TRIMMED(gdp);
> +	}
> 	ext4_group_desc_csum_set(sb, block_group, gdp);
> 	ext4_unlock_group(sb, block_group);
> 
> @@ -5425,6 +5438,7 @@ ext4_trim_all_free(struct super_block *sb, ext4_group_t group,
> 		}
> 		ext4_lock_group(sb, group);
> 		EXT4_MB_GDP_SET_TRIMMED(gdp);
> +		e4b.bd_info->bb_freed_last_trimmed = 0;
> 		ext4_group_desc_csum_set(sb, group, gdp);
> 		ext4_unlock_group(sb, group);
> 		err = ext4_handle_dirty_metadata(handle, NULL, gdp_bh);
> diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c
> index 6c9fc9e21c13..8ee4e7e3f125 100644
> --- a/fs/ext4/sysfs.c
> +++ b/fs/ext4/sysfs.c
> @@ -216,6 +216,7 @@ EXT4_RW_ATTR_SBI_UI(mb_order2_req, s_mb_order2_reqs);
> EXT4_RW_ATTR_SBI_UI(mb_stream_req, s_mb_stream_request);
> EXT4_RW_ATTR_SBI_UI(mb_group_prealloc, s_mb_group_prealloc);
> EXT4_RW_ATTR_SBI_UI(extent_max_zeroout_kb, s_extent_max_zeroout_kb);
> +EXT4_RW_ATTR_SBI_UI(min_freed_blocks_to_trim, s_min_freed_blocks_to_trim);
> EXT4_ATTR(trigger_fs_error, 0200, trigger_test_error);
> EXT4_RW_ATTR_SBI_UI(err_ratelimit_interval_ms, s_err_ratelimit_state.interval);
> EXT4_RW_ATTR_SBI_UI(err_ratelimit_burst, s_err_ratelimit_state.burst);
> @@ -259,6 +260,7 @@ static struct attribute *ext4_attrs[] = {
> 	ATTR_LIST(mb_group_prealloc),
> 	ATTR_LIST(max_writeback_mb_bump),
> 	ATTR_LIST(extent_max_zeroout_kb),
> +	ATTR_LIST(min_freed_blocks_to_trim),
> 	ATTR_LIST(trigger_fs_error),
> 	ATTR_LIST(err_ratelimit_interval_ms),
> 	ATTR_LIST(err_ratelimit_burst),
> --
> 2.25.4
> 


Cheers, Andreas






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