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Date: Wed, 27 May 2020 12:21:58 +0200
From: Lukas Czerner <lczerner@...hat.com>
To: Wang Shilong <wangshilong1991@...il.com>
Cc: Ext4 Developers List <linux-ext4@...r.kernel.org>,
Wang Shilong <wshilong@....com>,
Shuichi Ihara <sihara@....com>,
Andreas Dilger <adilger@...ger.ca>
Subject: Re: [PATCH] ext4: introduce EXT4_BG_WAS_TRIMMED to optimize trim
On Wed, May 27, 2020 at 06:06:09PM +0800, Wang Shilong wrote:
> On Wed, May 27, 2020 at 5:19 PM Lukas Czerner <lczerner@...hat.com> wrote:
> >
> > On Wed, May 27, 2020 at 04:38:50PM +0900, Wang Shilong wrote:
> > > From: Wang Shilong <wshilong@....com>
> > >
> > > Currently WAS_TRIMMED flag is not persistent, whenever filesystem was
> > > remounted, fstrim need walk all block groups again, the problem with
> > > this is FSTRIM could be slow on very large LUN SSD based filesystem.
> > >
> > > To avoid this kind of problem, we introduce a block group flag
> > > EXT4_BG_WAS_TRIMMED, the side effect of this is we need introduce
> > > extra one block group dirty write after trimming block group.
> >
> > Hi
> >
> > that's fair enough, however once you make this persistent we also need
> > to have a way to clear the flag, or at least bypass it. Storage can be
> > changed and if it does we might want to re-run the fstrim.
>
> Yup, i thought about that.
>
> 1) we might add an mount option or sys interface, something force_fstrim
> 2) Add an option to e2fsck to force clear this block group flag.
Option for tune2fs to clear the flags sounds way better than yet another
mount option.
Thanks!
-Lukas
>
> >
> > We also need to set this flag in mke2fs and e2fsck if appropriate.
> >
>
> Good point.
>
> > more below...
> >
> > >
> > > And When clearing TRIMMED flag, block group will be journalled
> > > anyway, so it won't introduce any overhead.
> > >
> > > Cc: Shuichi Ihara <sihara@....com>
> > > Cc: Andreas Dilger <adilger@...ger.ca>
> > > Cc: Wang Shilong <wangshilong1991@...il.com>
> > > Signed-off-by: Wang Shilong <wshilong@....com>
> > > ---
> > > fs/ext4/ext4.h | 18 +++++++--------
> > > fs/ext4/ext4_jbd2.h | 3 ++-
> > > fs/ext4/mballoc.c | 54 ++++++++++++++++++++++++++++++++++-----------
> > > 3 files changed, 52 insertions(+), 23 deletions(-)
> > >
> > > diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> > > index ad2dbf6e4924..23c2dc529a28 100644
> > > --- a/fs/ext4/ext4.h
> > > +++ b/fs/ext4/ext4.h
> > > @@ -357,6 +357,7 @@ struct flex_groups {
> > > #define EXT4_BG_INODE_UNINIT 0x0001 /* Inode table/bitmap not in use */
> > > #define EXT4_BG_BLOCK_UNINIT 0x0002 /* Block bitmap not in use */
> > > #define EXT4_BG_INODE_ZEROED 0x0004 /* On-disk itable initialized to zero */
> > > +#define EXT4_BG_WAS_TRIMMED 0x0008 /* block group was trimmed */
> > >
> > > /*
> > > * Macro-instructions used to manage group descriptors
> > > @@ -3112,9 +3113,8 @@ struct ext4_group_info {
> > > };
> > >
> > > #define EXT4_GROUP_INFO_NEED_INIT_BIT 0
> > > -#define EXT4_GROUP_INFO_WAS_TRIMMED_BIT 1
> > > -#define EXT4_GROUP_INFO_BBITMAP_CORRUPT_BIT 2
> > > -#define EXT4_GROUP_INFO_IBITMAP_CORRUPT_BIT 3
> > > +#define EXT4_GROUP_INFO_BBITMAP_CORRUPT_BIT 1
> > > +#define EXT4_GROUP_INFO_IBITMAP_CORRUPT_BIT 2
> > > #define EXT4_GROUP_INFO_BBITMAP_CORRUPT \
> > > (1 << EXT4_GROUP_INFO_BBITMAP_CORRUPT_BIT)
> > > #define EXT4_GROUP_INFO_IBITMAP_CORRUPT \
> > > @@ -3127,12 +3127,12 @@ struct ext4_group_info {
> > > #define EXT4_MB_GRP_IBITMAP_CORRUPT(grp) \
> > > (test_bit(EXT4_GROUP_INFO_IBITMAP_CORRUPT_BIT, &((grp)->bb_state)))
> > >
> > > -#define EXT4_MB_GRP_WAS_TRIMMED(grp) \
> > > - (test_bit(EXT4_GROUP_INFO_WAS_TRIMMED_BIT, &((grp)->bb_state)))
> > > -#define EXT4_MB_GRP_SET_TRIMMED(grp) \
> > > - (set_bit(EXT4_GROUP_INFO_WAS_TRIMMED_BIT, &((grp)->bb_state)))
> > > -#define EXT4_MB_GRP_CLEAR_TRIMMED(grp) \
> > > - (clear_bit(EXT4_GROUP_INFO_WAS_TRIMMED_BIT, &((grp)->bb_state)))
> > > +#define EXT4_MB_GDP_WAS_TRIMMED(gdp) \
> > > + (gdp->bg_flags & cpu_to_le16(EXT4_BG_WAS_TRIMMED))
> > > +#define EXT4_MB_GDP_SET_TRIMMED(gdp) \
> > > + (gdp->bg_flags |= cpu_to_le16(EXT4_BG_WAS_TRIMMED))
> > > +#define EXT4_MB_GDP_CLEAR_TRIMMED(gdp) \
> > > + (gdp->bg_flags &= ~cpu_to_le16(EXT4_BG_WAS_TRIMMED))
> > >
> > > #define EXT4_MAX_CONTENTION 8
> > > #define EXT4_CONTENTION_THRESHOLD 2
> > > diff --git a/fs/ext4/ext4_jbd2.h b/fs/ext4/ext4_jbd2.h
> > > index 4b9002f0e84c..4094a5b247f7 100644
> > > --- a/fs/ext4/ext4_jbd2.h
> > > +++ b/fs/ext4/ext4_jbd2.h
> > > @@ -123,7 +123,8 @@
> > > #define EXT4_HT_MOVE_EXTENTS 9
> > > #define EXT4_HT_XATTR 10
> > > #define EXT4_HT_EXT_CONVERT 11
> > > -#define EXT4_HT_MAX 12
> > > +#define EXT4_HT_FS_TRIM 12
> > > +#define EXT4_HT_MAX 13
> > >
> > > /**
> > > * struct ext4_journal_cb_entry - Base structure for callback information.
> > > diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> > > index 30d5d97548c4..d25377948994 100644
> > > --- a/fs/ext4/mballoc.c
> > > +++ b/fs/ext4/mballoc.c
> > > @@ -2829,15 +2829,6 @@ static void ext4_free_data_in_buddy(struct super_block *sb,
> > > rb_erase(&entry->efd_node, &(db->bb_free_root));
> > > mb_free_blocks(NULL, &e4b, entry->efd_start_cluster, entry->efd_count);
> > >
> > > - /*
> > > - * Clear the trimmed flag for the group so that the next
> > > - * ext4_trim_fs can trim it.
> > > - * If the volume is mounted with -o discard, online discard
> > > - * is supported and the free blocks will be trimmed online.
> > > - */
> > > - if (!test_opt(sb, DISCARD))
> > > - EXT4_MB_GRP_CLEAR_TRIMMED(db);
> > > -
> > > if (!db->bb_free_root.rb_node) {
> > > /* No more items in the per group rb tree
> > > * balance refcounts from ext4_mb_free_metadata()
> > > @@ -4928,8 +4919,7 @@ void ext4_free_blocks(handle_t *handle, struct inode *inode,
> > > " group:%d block:%d count:%lu failed"
> > > " with %d", block_group, bit, count,
> > > err);
> > > - } else
> > > - EXT4_MB_GRP_CLEAR_TRIMMED(e4b.bd_info);
> > > + }
> > >
> > > ext4_lock_group(sb, block_group);
> > > mb_clear_bits(bitmap_bh->b_data, bit, count_clusters);
> > > @@ -4939,6 +4929,14 @@ void ext4_free_blocks(handle_t *handle, struct inode *inode,
> > > ret = ext4_free_group_clusters(sb, gdp) + count_clusters;
> > > ext4_free_group_clusters_set(sb, gdp, ret);
> > > ext4_block_bitmap_csum_set(sb, block_group, gdp, bitmap_bh);
> > > + /*
> > > + * Clear the trimmed flag for the group so that the next
> > > + * ext4_trim_fs can trim it.
> > > + * If the volume is mounted with -o discard, online discard
> > > + * is supported and the free blocks will be trimmed online.
> > > + */
> > > + if (!test_opt(sb, DISCARD))
> > > + EXT4_MB_GDP_CLEAR_TRIMMED(gdp);
> > > ext4_group_desc_csum_set(sb, block_group, gdp);
> > > ext4_unlock_group(sb, block_group);
> > >
> > > @@ -5192,8 +5190,15 @@ ext4_trim_all_free(struct super_block *sb, ext4_group_t group,
> > > ext4_grpblk_t next, count = 0, free_count = 0;
> > > struct ext4_buddy e4b;
> > > int ret = 0;
> > > + struct ext4_group_desc *gdp;
> > > + struct buffer_head *gdp_bh;
> > >
> > > trace_ext4_trim_all_free(sb, group, start, max);
> > > + gdp = ext4_get_group_desc(sb, group, &gdp_bh);
> > > + if (!gdp) {
> > > + ret = -EIO;
> > > + return ret;
> > > + }
> > >
> > > ret = ext4_mb_load_buddy(sb, group, &e4b);
> > > if (ret) {
> > > @@ -5204,7 +5209,7 @@ ext4_trim_all_free(struct super_block *sb, ext4_group_t group,
> > > bitmap = e4b.bd_bitmap;
> > >
> > > ext4_lock_group(sb, group);
> > > - if (EXT4_MB_GRP_WAS_TRIMMED(e4b.bd_info) &&
> > > + if (EXT4_MB_GDP_WAS_TRIMMED(gdp) &&
> > > minblocks >= atomic_read(&EXT4_SB(sb)->s_last_trim_minblks))
> > > goto out;
> > >
> > > @@ -5245,12 +5250,35 @@ ext4_trim_all_free(struct super_block *sb, ext4_group_t group,
> > >
> > > if (!ret) {
> > > ret = count;
> > > - EXT4_MB_GRP_SET_TRIMMED(e4b.bd_info);
> > > + EXT4_MB_GDP_SET_TRIMMED(gdp);
> > > + ext4_group_desc_csum_set(sb, group, gdp);
> > > }
> > > out:
> > > ext4_unlock_group(sb, group);
> > > ext4_mb_unload_buddy(&e4b);
> > > + if (ret > 0) {
> > > + int err;
> > > + handle_t *handle;
> > >
> > > + handle = ext4_journal_start_sb(sb, EXT4_HT_FS_TRIM, 1);
> > > + if (IS_ERR(handle)) {
> > > + ret = PTR_ERR(handle);
> > > + goto out_return;
> > > + }
> > > + err = ext4_journal_get_write_access(handle, gdp_bh);
> > > + if (err) {
> > > + ret = err;
> > > + goto out_journal;
> > > + }
> >
> > Don't we need to do this before we set the flag in gdp?
> >
>
> Sorry about this, you are right.
>
> > -Lukas
> >
> > > + err = ext4_handle_dirty_metadata(handle, NULL, gdp_bh);
> > > + if (err)
> > > + ret = err;
> > > +out_journal:
> > > + err = ext4_journal_stop(handle);
> > > + if (err)
> > > + ret = err;
> > > + }
> > > +out_return:
> > > ext4_debug("trimmed %d blocks in the group %d\n",
> > > count, group);
> > >
> > > --
> > > 2.25.4
> > >
> >
>
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