On Tue 09-01-24 19:28:07, Fengnan Chang wrote:
> Jan Kara <jack@xxxxxxx> 于2024年1月9日周二 01:15写道：
> >
> > On Fri 01-09-23 17:28:20, 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.
> > >
> > > Signed-off-by: Fengnan Chang <changfengnan@xxxxxxxxxxxxx>
> >
> > This seems to have fallen through the cracks... I'm sorry for that.
> >
> > > 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);
> >
> > Is the single extent case really worth the complications to save one
> > allocation? I don't think it is but maybe I'm missing something. Otherwise
> > the patch looks good to me!
> yeah, it's necessary, if there is only one segment, alloc memory may cause
> performance regression.
> Refer to this https://lore.kernel.org/linux-ext4/CALWNXx-6y0=ZDBMicv2qng9pKHWcpJbCvUm9TaRBwg81WzWkWQ@xxxxxxxxxxxxxx/
Ah, thanks for the reference! Then what I'd suggest is something like:
struct ext4_free_data first_entry;
/*
* We preallocate the first entry on stack to optimize for the common
* case of trimming single extent in each group. It has measurable
* performance impact.
*/
struct ext4_free_data *entry = &first_entry;
then when we allocate we do:
if (!entry)
entry = kmem_cache_alloc(...)
entry->efd_start_cluster = start;
entry->efd_count = next - start;
list_add_tail(&entry->efd_list, &discard_data_list);
entry = NULL;
and then when freeing we can have:
list_for_each_entry_safe(fd, nfd, &discard_data_list, efd_list) {
mb_free_blocks(NULL, e4b, fd->efd_start_cluster, fd->efd_count);
if (fd != &first_entry)
kmem_cache_free(ext4_free_data_cachep, fd);
}
Then it is more understandable what's going on...
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
