Date:   Mon, 22 Jun 2020 11:18:24 -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 v3 1/2] ext4: introduce EXT4_BG_WAS_TRIMMED to optimize
 trim

On Jun 22, 2020, at 7:14 AM, Wang Shilong <wangshilong1991@...il.com> wrote:
> 
> From: Wang Shilong <wshilong@....com>
> 
> Currently WAS_TRIMMED flag is not persistent, whenever filesystem was
> remounted, fstrim need walk all block groups again, the problem with
> this is FSTRIM could be slow on very large LUN SSD based filesystem.
> 
> To avoid this kind of problem, we introduce a block group flag
> EXT4_BG_WAS_TRIMMED, the side effect of this is we need introduce
> extra one block group dirty write after trimming block group.
> 
> And When clearing TRIMMED flag, block group will be journalled
> anyway, so it won't introduce any overhead.
> 
> 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>

> ---
> v2->v3:
> don't renumber EXT4_GROUP_INFO_* bits.
> v1->v2:
> call ext4_journal_get_write_access() before modify buffer.
> ---
> fs/ext4/ext4.h      | 14 +++++------
> fs/ext4/ext4_jbd2.h |  3 ++-
> fs/ext4/mballoc.c   | 59 +++++++++++++++++++++++++++++++++------------
> 3 files changed, 53 insertions(+), 23 deletions(-)
> 
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 42f5060f3cdf..252754da2f1b 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -368,6 +368,7 @@ struct flex_groups {
> #define EXT4_BG_INODE_UNINIT	0x0001 /* Inode table/bitmap not in use */
> #define EXT4_BG_BLOCK_UNINIT	0x0002 /* Block bitmap not in use */
> #define EXT4_BG_INODE_ZEROED	0x0004 /* On-disk itable initialized to zero */
> +#define EXT4_BG_WAS_TRIMMED	0x0008 /* block group was trimmed */
> 
> /*
>  * Macro-instructions used to manage group descriptors
> @@ -3138,7 +3139,6 @@ struct ext4_group_info {
> };
> 
> #define EXT4_GROUP_INFO_NEED_INIT_BIT		0
> -#define EXT4_GROUP_INFO_WAS_TRIMMED_BIT		1
> #define EXT4_GROUP_INFO_BBITMAP_CORRUPT_BIT	2
> #define EXT4_GROUP_INFO_IBITMAP_CORRUPT_BIT	3
> #define EXT4_GROUP_INFO_BBITMAP_CORRUPT		\
> @@ -3153,12 +3153,12 @@ struct ext4_group_info {
> #define EXT4_MB_GRP_IBITMAP_CORRUPT(grp)	\
> 	(test_bit(EXT4_GROUP_INFO_IBITMAP_CORRUPT_BIT, &((grp)->bb_state)))
> 
> -#define EXT4_MB_GRP_WAS_TRIMMED(grp)	\
> -	(test_bit(EXT4_GROUP_INFO_WAS_TRIMMED_BIT, &((grp)->bb_state)))
> -#define EXT4_MB_GRP_SET_TRIMMED(grp)	\
> -	(set_bit(EXT4_GROUP_INFO_WAS_TRIMMED_BIT, &((grp)->bb_state)))
> -#define EXT4_MB_GRP_CLEAR_TRIMMED(grp)	\
> -	(clear_bit(EXT4_GROUP_INFO_WAS_TRIMMED_BIT, &((grp)->bb_state)))
> +#define EXT4_MB_GDP_WAS_TRIMMED(gdp)	\
> +	(gdp->bg_flags & cpu_to_le16(EXT4_BG_WAS_TRIMMED))
> +#define EXT4_MB_GDP_SET_TRIMMED(gdp)	\
> +	(gdp->bg_flags |= cpu_to_le16(EXT4_BG_WAS_TRIMMED))
> +#define EXT4_MB_GDP_CLEAR_TRIMMED(gdp)	\
> +	(gdp->bg_flags &= ~cpu_to_le16(EXT4_BG_WAS_TRIMMED))
> 
> #define EXT4_MAX_CONTENTION		8
> #define EXT4_CONTENTION_THRESHOLD	2
> diff --git a/fs/ext4/ext4_jbd2.h b/fs/ext4/ext4_jbd2.h
> index 00dc668e052b..a37e438f4b4d 100644
> --- a/fs/ext4/ext4_jbd2.h
> +++ b/fs/ext4/ext4_jbd2.h
> @@ -123,7 +123,8 @@
> #define EXT4_HT_MOVE_EXTENTS     9
> #define EXT4_HT_XATTR           10
> #define EXT4_HT_EXT_CONVERT     11
> -#define EXT4_HT_MAX             12
> +#define EXT4_HT_FS_TRIM		12
> +#define EXT4_HT_MAX             13
> 
> /**
>  *   struct ext4_journal_cb_entry - Base structure for callback information.
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index c0a331e2feb0..235a316584d0 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -2923,15 +2923,6 @@ static void ext4_free_data_in_buddy(struct super_block *sb,
> 	rb_erase(&entry->efd_node, &(db->bb_free_root));
> 	mb_free_blocks(NULL, &e4b, entry->efd_start_cluster, entry->efd_count);
> 
> -	/*
> -	 * Clear the trimmed flag for the group so that the next
> -	 * ext4_trim_fs can trim it.
> -	 * 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_GRP_CLEAR_TRIMMED(db);
> -
> 	if (!db->bb_free_root.rb_node) {
> 		/* No more items in the per group rb tree
> 		 * balance refcounts from ext4_mb_free_metadata()
> @@ -5084,8 +5075,7 @@ void ext4_free_blocks(handle_t *handle, struct inode *inode,
> 					 " group:%d block:%d count:%lu failed"
> 					 " with %d", block_group, bit, count,
> 					 err);
> -		} else
> -			EXT4_MB_GRP_CLEAR_TRIMMED(e4b.bd_info);
> +		}
> 
> 		ext4_lock_group(sb, block_group);
> 		mb_clear_bits(bitmap_bh->b_data, bit, count_clusters);
> @@ -5095,6 +5085,14 @@ void ext4_free_blocks(handle_t *handle, struct inode *inode,
> 	ret = ext4_free_group_clusters(sb, gdp) + count_clusters;
> 	ext4_free_group_clusters_set(sb, gdp, ret);
> 	ext4_block_bitmap_csum_set(sb, block_group, gdp, bitmap_bh);
> +	/*
> +	 * Clear the trimmed flag for the group so that the next
> +	 * ext4_trim_fs can trim it.
> +	 * 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);
> 	ext4_group_desc_csum_set(sb, block_group, gdp);
> 	ext4_unlock_group(sb, block_group);
> 
> @@ -5348,8 +5346,15 @@ ext4_trim_all_free(struct super_block *sb, ext4_group_t group,
> 	ext4_grpblk_t next, count = 0, free_count = 0;
> 	struct ext4_buddy e4b;
> 	int ret = 0;
> +	struct ext4_group_desc *gdp;
> +	struct buffer_head *gdp_bh;
> 
> 	trace_ext4_trim_all_free(sb, group, start, max);
> +	gdp = ext4_get_group_desc(sb, group, &gdp_bh);
> +	if (!gdp) {
> +		ret = -EIO;
> +		return ret;
> +	}
> 
> 	ret = ext4_mb_load_buddy(sb, group, &e4b);
> 	if (ret) {
> @@ -5360,7 +5365,7 @@ ext4_trim_all_free(struct super_block *sb, ext4_group_t group,
> 	bitmap = e4b.bd_bitmap;
> 
> 	ext4_lock_group(sb, group);
> -	if (EXT4_MB_GRP_WAS_TRIMMED(e4b.bd_info) &&
> +	if (EXT4_MB_GDP_WAS_TRIMMED(gdp) &&
> 	    minblocks >= atomic_read(&EXT4_SB(sb)->s_last_trim_minblks))
> 		goto out;
> 
> @@ -5399,14 +5404,38 @@ ext4_trim_all_free(struct super_block *sb, ext4_group_t group,
> 			break;
> 	}
> 
> -	if (!ret) {
> +	if (!ret)
> 		ret = count;
> -		EXT4_MB_GRP_SET_TRIMMED(e4b.bd_info);
> -	}
> out:
> 	ext4_unlock_group(sb, group);
> 	ext4_mb_unload_buddy(&e4b);
> +	if (ret > 0) {
> +		int err;
> +		handle_t *handle;
> 
> +		handle = ext4_journal_start_sb(sb, EXT4_HT_FS_TRIM, 1);
> +		if (IS_ERR(handle)) {
> +			ret = PTR_ERR(handle);
> +			goto out_return;
> +		}
> +		err = ext4_journal_get_write_access(handle, gdp_bh);
> +		if (err) {
> +			ret = err;
> +			goto out_journal;
> +		}
> +		ext4_lock_group(sb, group);
> +		EXT4_MB_GDP_SET_TRIMMED(gdp);
> +		ext4_group_desc_csum_set(sb, group, gdp);
> +		ext4_unlock_group(sb, group);
> +		err = ext4_handle_dirty_metadata(handle, NULL, gdp_bh);
> +		if (err)
> +			ret = err;
> +out_journal:
> +		err = ext4_journal_stop(handle);
> +		if (err)
> +			ret = err;
> +	}
> +out_return:
> 	ext4_debug("trimmed %d blocks in the group %d\n",
> 		count, group);
> 
> --
> 2.25.4
> 


Cheers, Andreas






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