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Message-ID: <CAPFOzZtbst7XuaEWe=H8G2tpPDBDHbFuR3PR064pMbyDEzkyJg@mail.gmail.com>
Date: Fri, 1 Sep 2023 16:31:50 +0800
From: Fengnan Chang <changfengnan@...edance.com>
To: tytso@....edu, adilger.kernel@...ger.ca
Cc: linux-ext4@...r.kernel.org
Subject: Re: [PATCH v5] ext4: improve trim efficiency
Fengnan Chang <changfengnan@...edance.com> 于2023年8月24日周四 14:21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..86857b22c4bc 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)
In old way, when the device not support discard, it still continue the loop.
I modified this logic and let it break the loop in this patch, but it may cause
free_count = 0, and cause a wan log in mb_free_blocks, I'll fix this in the
next version.
Thanks.
> + 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)
> + 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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