Re: [External] Re: [PATCH v3] ext4: improve trim efficiency

[Fengnan Chang <changfengnan@bytedance.com>]

Hi Ted, Andreas:
    Any comments ?

Thanks.

Guoqing Jiang <guoqing.jiang@linux.dev> 于2023年7月31日周一 10:27写道：
>
>
>
> On 7/25/23 20:18, Fengnan Chang wrote:
> > 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.
> >
> > Reported-by: kernel test robot <oliver.sang@intel.com>
> > Closes: https://lore.kernel.org/oe-lkp/202307171455.ee68ef8b-oliver.sang@intel.com
> > Signed-off-by: Fengnan Chang <changfengnan@bytedance.com>
> > ---
> >   fs/ext4/mballoc.c | 49 +++++++++++++++++++++++++++++++++++++++++------
> >   1 file changed, 43 insertions(+), 6 deletions(-)
> >
> > diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> > index a2475b8c9fb5..b75ca1df0d30 100644
> > --- a/fs/ext4/mballoc.c
> > +++ b/fs/ext4/mballoc.c
> > @@ -6790,7 +6790,8 @@ int ext4_group_add_blocks(handle_t *handle, struct super_block *sb,
> >    * be called with under the group lock.
> >    */
> >   static int ext4_trim_extent(struct super_block *sb,
> > -             int start, int count, struct ext4_buddy *e4b)
> > +             int start, int count, bool noalloc, struct ext4_buddy *e4b,
> > +             struct bio **biop, struct ext4_free_data **entryp)
> >   __releases(bitlock)
> >   __acquires(bitlock)
> >   {
> > @@ -6812,9 +6813,16 @@ __acquires(bitlock)
> >        */
> >       mb_mark_used(e4b, &ex);
> >       ext4_unlock_group(sb, group);
> > -     ret = ext4_issue_discard(sb, group, start, count, NULL);
> > +     ret = ext4_issue_discard(sb, group, start, count, biop);
> > +     if (!ret && !noalloc) {
> > +             struct ext4_free_data *entry = kmem_cache_alloc(ext4_free_data_cachep,
> > +                             GFP_NOFS|__GFP_NOFAIL);
> > +             entry->efd_start_cluster = start;
> > +             entry->efd_count = count;
> > +             *entryp  = entry;
> > +     }
> > +
> >       ext4_lock_group(sb, group);
> > -     mb_free_blocks(NULL, e4b, start, ex.fe_len);
> >       return ret;
> >   }
> >
> > @@ -6824,26 +6832,40 @@ static int ext4_try_to_trim_range(struct super_block *sb,
> >   __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;
> > +     bool noalloc = false;
> > +
> > +     INIT_LIST_HEAD(&discard_data_list);
> >
> >       bitmap = e4b->bd_bitmap;
> >       start = (e4b->bd_info->bb_first_free > start) ?
> >               e4b->bd_info->bb_first_free : start;
> >       count = 0;
> >       free_count = 0;
> > +     bak = start;
> >
> > +     blk_start_plug(&plug);
> >       while (start <= max) {
> >               start = mb_find_next_zero_bit(bitmap, max + 1, start);
> >               if (start > max)
> >                       break;
> >               next = mb_find_next_bit(bitmap, max + 1, start);
> > +             /* when only one segment, there is no need to alloc entry */
> > +             noalloc = (free_count == 0) && (next >= max);
> >
> >               if ((next - start) >= minblocks) {
> > -                     int ret = ext4_trim_extent(sb, start, next - start, e4b);
> > +                     int ret = ext4_trim_extent(sb, start, next - start, noalloc, e4b,
> > +                                                     &discard_bio, &entry);
> >
> > -                     if (ret && ret != -EOPNOTSUPP)
> > +                     if (ret < 0)
> >                               break;
> > +                     if (entry)
> > +                             list_add_tail(&entry->efd_list, &discard_data_list);
> >                       count += next - start;
> >               }
> >               free_count += next - start;
> > @@ -6863,6 +6885,21 @@ __releases(ext4_group_lock_ptr(sb, e4b->bd_group))
> >               if ((e4b->bd_info->bb_free - free_count) < minblocks)
> >                       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;
> >   }
>
> With the new version, I don't see big difference from my test.
>
> Thanks,
> Guoqing