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Message-ID: <20240109120852.jospfnxmeeusbxnm@quack3> Date: Tue, 9 Jan 2024 13:08:52 +0100 From: Jan Kara <jack@...e.cz> To: Fengnan Chang <changfengnan@...edance.com> Cc: Jan Kara <jack@...e.cz>, tytso@....edu, adilger.kernel@...ger.ca, linux-ext4@...r.kernel.org Subject: Re: [External] Re: [PATCH v6] ext4: improve trim efficiency On Tue 09-01-24 19:28:07, Fengnan Chang wrote: > Jan Kara <jack@...e.cz> 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@...edance.com> > > > > 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@mail.gmail.com/ 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@...e.com> SUSE Labs, CR
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