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Date:   Thu, 12 Oct 2023 19:57:48 +0800
From:   Fengnan Chang <changfengnan@...edance.com>
To:     tytso@....edu, adilger.kernel@...ger.ca
Cc:     linux-ext4@...r.kernel.org
Subject: Re: [PATCH v6] ext4: improve trim efficiency

Hi Ted:
    any new comments ?

Fengnan Chang <changfengnan@...edance.com> 于2023年9月1日周五 17:28写道:
>
> In commit a015434480dc("ext4: send parallel discards on commit
> completions"), issue all discard commands in parallel make all
> bios could merged into one request, so lowlevel drive can issue
> multi segments in one time which is more efficiency, but commit
> 55cdd0af2bc5 ("ext4: get discard out of jbd2 commit kthread contex")
> seems broke this way, let's fix it.
>
> In my test:
> 1. create 10 normal files, each file size is 10G.
> 2. deallocate file, punch a 16k holes every 32k.
> 3. trim all fs.
> the time of fstrim fs reduce from 6.7s to 1.3s.
>
> Signed-off-by: Fengnan Chang <changfengnan@...edance.com>
> ---
>  fs/ext4/mballoc.c | 95 +++++++++++++++++++++++++----------------------
>  1 file changed, 51 insertions(+), 44 deletions(-)
>
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 1e4c667812a9..9fc69a92c496 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -6874,70 +6874,61 @@ int ext4_group_add_blocks(handle_t *handle, struct super_block *sb,
>         return err;
>  }
>
> -/**
> - * ext4_trim_extent -- function to TRIM one single free extent in the group
> - * @sb:                super block for the file system
> - * @start:     starting block of the free extent in the alloc. group
> - * @count:     number of blocks to TRIM
> - * @e4b:       ext4 buddy for the group
> - *
> - * Trim "count" blocks starting at "start" in the "group". To assure that no
> - * one will allocate those blocks, mark it as used in buddy bitmap. This must
> - * be called with under the group lock.
> - */
> -static int ext4_trim_extent(struct super_block *sb,
> -               int start, int count, struct ext4_buddy *e4b)
> -__releases(bitlock)
> -__acquires(bitlock)
> -{
> -       struct ext4_free_extent ex;
> -       ext4_group_t group = e4b->bd_group;
> -       int ret = 0;
> -
> -       trace_ext4_trim_extent(sb, group, start, count);
> -
> -       assert_spin_locked(ext4_group_lock_ptr(sb, group));
> -
> -       ex.fe_start = start;
> -       ex.fe_group = group;
> -       ex.fe_len = count;
> -
> -       /*
> -        * Mark blocks used, so no one can reuse them while
> -        * being trimmed.
> -        */
> -       mb_mark_used(e4b, &ex);
> -       ext4_unlock_group(sb, group);
> -       ret = ext4_issue_discard(sb, group, start, count, NULL);
> -       ext4_lock_group(sb, group);
> -       mb_free_blocks(NULL, e4b, start, ex.fe_len);
> -       return ret;
> -}
> -
>  static int ext4_try_to_trim_range(struct super_block *sb,
>                 struct ext4_buddy *e4b, ext4_grpblk_t start,
>                 ext4_grpblk_t max, ext4_grpblk_t minblocks)
>  __acquires(ext4_group_lock_ptr(sb, e4b->bd_group))
>  __releases(ext4_group_lock_ptr(sb, e4b->bd_group))
>  {
> -       ext4_grpblk_t next, count, free_count;
> +       ext4_grpblk_t next, count, free_count, bak;
>         void *bitmap;
> +       struct ext4_free_data *entry = NULL, *fd, *nfd;
> +       struct list_head discard_data_list;
> +       struct bio *discard_bio = NULL;
> +       struct blk_plug plug;
> +       ext4_group_t group = e4b->bd_group;
> +       struct ext4_free_extent ex;
> +       bool noalloc = false;
> +       int ret = 0;
> +
> +       INIT_LIST_HEAD(&discard_data_list);
>
>         bitmap = e4b->bd_bitmap;
>         start = max(e4b->bd_info->bb_first_free, start);
>         count = 0;
>         free_count = 0;
>
> +       blk_start_plug(&plug);
>         while (start <= max) {
>                 start = mb_find_next_zero_bit(bitmap, max + 1, start);
>                 if (start > max)
>                         break;
> +               bak = start;
>                 next = mb_find_next_bit(bitmap, max + 1, start);
> -
>                 if ((next - start) >= minblocks) {
> -                       int ret = ext4_trim_extent(sb, start, next - start, e4b);
> +                       /* when only one segment, there is no need to alloc entry */
> +                       noalloc = (free_count == 0) && (next >= max);
>
> -                       if (ret && ret != -EOPNOTSUPP)
> +                       trace_ext4_trim_extent(sb, group, start, next - start);
> +                       ex.fe_start = start;
> +                       ex.fe_group = group;
> +                       ex.fe_len = next - start;
> +                       /*
> +                        * Mark blocks used, so no one can reuse them while
> +                        * being trimmed.
> +                        */
> +                       mb_mark_used(e4b, &ex);
> +                       ext4_unlock_group(sb, group);
> +                       ret = ext4_issue_discard(sb, group, start, next - start, &discard_bio);
> +                       if (!noalloc) {
> +                               entry = kmem_cache_alloc(ext4_free_data_cachep,
> +                                                       GFP_NOFS|__GFP_NOFAIL);
> +                               entry->efd_start_cluster = start;
> +                               entry->efd_count = next - start;
> +                               list_add_tail(&entry->efd_list, &discard_data_list);
> +                       }
> +                       ext4_lock_group(sb, group);
> +                       if (ret < 0)
>                                 break;
>                         count += next - start;
>                 }
> @@ -6959,6 +6950,22 @@ __releases(ext4_group_lock_ptr(sb, e4b->bd_group))
>                         break;
>         }
>
> +       if (discard_bio) {
> +               ext4_unlock_group(sb, e4b->bd_group);
> +               submit_bio_wait(discard_bio);
> +               bio_put(discard_bio);
> +               ext4_lock_group(sb, e4b->bd_group);
> +       }
> +       blk_finish_plug(&plug);
> +
> +       if (noalloc && free_count)
> +               mb_free_blocks(NULL, e4b, bak, free_count);
> +
> +       list_for_each_entry_safe(fd, nfd, &discard_data_list, efd_list) {
> +               mb_free_blocks(NULL, e4b, fd->efd_start_cluster, fd->efd_count);
> +               kmem_cache_free(ext4_free_data_cachep, fd);
> +       }
> +
>         return count;
>  }
>
> --
> 2.20.1
>

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