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Message-ID: <20200403162052.GA68460@google.com>
Date: Fri, 3 Apr 2020 09:20:52 -0700
From: Jaegeuk Kim <jaegeuk@...nel.org>
To: Chao Yu <yuchao0@...wei.com>
Cc: Sahitya Tummala <stummala@...eaurora.org>,
linux-f2fs-devel@...ts.sourceforge.net,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] f2fs: prevent meta updates while checkpoint is in
progress
On 04/01, Chao Yu wrote:
> On 2020/4/1 2:43, Jaegeuk Kim wrote:
> > On 03/31, Sahitya Tummala wrote:
> >> On Mon, Mar 30, 2020 at 08:54:19PM -0700, Jaegeuk Kim wrote:
> >>> On 03/26, Sahitya Tummala wrote:
> >>>> allocate_segment_for_resize() can cause metapage updates if
> >>>> it requires to change the current node/data segments for resizing.
> >>>> Stop these meta updates when there is a checkpoint already
> >>>> in progress to prevent inconsistent CP data.
> >>>
> >>> I'd prefer to use f2fs_lock_op() in bigger coverage.
> >>
> >> Do you mean to cover the entire free_segment_range() function within
> >> f2fs_lock_op()? Please clarify.
> >
> > I didn't test tho, something like this?
> >
> > ---
> > fs/f2fs/checkpoint.c | 6 ++++--
> > fs/f2fs/f2fs.h | 2 +-
> > fs/f2fs/gc.c | 28 ++++++++++++++--------------
> > fs/f2fs/super.c | 1 -
> > include/trace/events/f2fs.h | 4 +++-
> > 5 files changed, 22 insertions(+), 19 deletions(-)
> >
> > diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> > index 852890b72d6ac..531995192b714 100644
> > --- a/fs/f2fs/checkpoint.c
> > +++ b/fs/f2fs/checkpoint.c
> > @@ -1553,7 +1553,8 @@ int f2fs_write_checkpoint(struct f2fs_sb_info *sbi, struct cp_control *cpc)
> > return 0;
> > f2fs_warn(sbi, "Start checkpoint disabled!");
> > }
> > - mutex_lock(&sbi->cp_mutex);
> > + if (cpc->reason != CP_RESIZE)
> > + mutex_lock(&sbi->cp_mutex);
> >
> > if (!is_sbi_flag_set(sbi, SBI_IS_DIRTY) &&
> > ((cpc->reason & CP_FASTBOOT) || (cpc->reason & CP_SYNC) ||
> > @@ -1622,7 +1623,8 @@ int f2fs_write_checkpoint(struct f2fs_sb_info *sbi, struct cp_control *cpc)
> > f2fs_update_time(sbi, CP_TIME);
> > trace_f2fs_write_checkpoint(sbi->sb, cpc->reason, "finish checkpoint");
> > out:
> > - mutex_unlock(&sbi->cp_mutex);
> > + if (cpc->reason != CP_RESIZE)
> > + mutex_unlock(&sbi->cp_mutex);
> > return err;
> > }
> >
> > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> > index c84442eefc56d..7c98dca3ec1d6 100644
> > --- a/fs/f2fs/f2fs.h
> > +++ b/fs/f2fs/f2fs.h
> > @@ -193,6 +193,7 @@ enum {
> > #define CP_DISCARD 0x00000010
> > #define CP_TRIMMED 0x00000020
> > #define CP_PAUSE 0x00000040
> > +#define CP_RESIZE 0x00000080
> >
> > #define MAX_DISCARD_BLOCKS(sbi) BLKS_PER_SEC(sbi)
> > #define DEF_MAX_DISCARD_REQUEST 8 /* issue 8 discards per round */
> > @@ -1417,7 +1418,6 @@ struct f2fs_sb_info {
> > unsigned int segs_per_sec; /* segments per section */
> > unsigned int secs_per_zone; /* sections per zone */
> > unsigned int total_sections; /* total section count */
> > - struct mutex resize_mutex; /* for resize exclusion */
> > unsigned int total_node_count; /* total node block count */
> > unsigned int total_valid_node_count; /* valid node block count */
> > loff_t max_file_blocks; /* max block index of file */
> > diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> > index 26248c8936db0..1e5a06fda09d3 100644
> > --- a/fs/f2fs/gc.c
> > +++ b/fs/f2fs/gc.c
> > @@ -1402,8 +1402,9 @@ void f2fs_build_gc_manager(struct f2fs_sb_info *sbi)
> > static int free_segment_range(struct f2fs_sb_info *sbi, unsigned int start,
> > unsigned int end)
> > {
> > - int type;
> > unsigned int segno, next_inuse;
> > + struct cp_control cpc = { CP_RESIZE, 0, 0, 0 };
> > + int type;
> > int err = 0;
> >
> > /* Move out cursegs from the target range */
> > @@ -1417,16 +1418,14 @@ static int free_segment_range(struct f2fs_sb_info *sbi, unsigned int start,
> > .iroot = RADIX_TREE_INIT(gc_list.iroot, GFP_NOFS),
> > };
> >
> > - down_write(&sbi->gc_lock);
> > do_garbage_collect(sbi, segno, &gc_list, FG_GC);
> > - up_write(&sbi->gc_lock);
> > put_gc_inode(&gc_list);
> >
> > if (get_valid_blocks(sbi, segno, true))
> > return -EAGAIN;
> > }
> >
> > - err = f2fs_sync_fs(sbi->sb, 1);
> > + err = f2fs_write_checkpoint(sbi, &cpc);
> > if (err)
> > return err;
> >
> > @@ -1502,6 +1501,7 @@ static void update_fs_metadata(struct f2fs_sb_info *sbi, int secs)
> > int f2fs_resize_fs(struct f2fs_sb_info *sbi, __u64 block_count)
> > {
> > __u64 old_block_count, shrunk_blocks;
> > + struct cp_control cpc = { CP_RESIZE, 0, 0, 0 };
> > unsigned int secs;
> > int gc_mode, gc_type;
> > int err = 0;
> > @@ -1538,7 +1538,9 @@ int f2fs_resize_fs(struct f2fs_sb_info *sbi, __u64 block_count)
> > return -EINVAL;
> > }
> >
> > - freeze_bdev(sbi->sb->s_bdev);
> > + freeze_super(sbi->sb);
>
> Look at this again, I guess holding freeze lock here may cause potential
> hang task issue, imaging that in a low-end storage, shrinking large size
> address space, free_segment_range() needs very long time to migrate all
> valid blocks in the tail of device, that's why previously we do block
> migration with small gc_lock coverage.
Hmm, it seems we had to do like:
1) do GC
2) freeze everything
3) check it's okay to go new metadata
4) do resize
5) thaw
>
> Quoted:
>
> Changelog v5 ==> v6:
> - In free_segment_range(), reduce granularity of gc_mutex.
>
> Thanks,
>
> > + down_write(&sbi->gc_lock);
> > + mutex_lock(&sbi->cp_mutex);
> >
> > shrunk_blocks = old_block_count - block_count;
> > secs = div_u64(shrunk_blocks, BLKS_PER_SEC(sbi));
> > @@ -1551,11 +1553,12 @@ int f2fs_resize_fs(struct f2fs_sb_info *sbi, __u64 block_count)
> > sbi->user_block_count -= shrunk_blocks;
> > spin_unlock(&sbi->stat_lock);
> > if (err) {
> > - thaw_bdev(sbi->sb->s_bdev, sbi->sb);
> > + mutex_unlock(&sbi->cp_mutex);
> > + up_write(&sbi->gc_lock);
> > + thaw_super(sbi->sb);
> > return err;
> > }
> >
> > - mutex_lock(&sbi->resize_mutex);
> > set_sbi_flag(sbi, SBI_IS_RESIZEFS);
> >
> > mutex_lock(&DIRTY_I(sbi)->seglist_lock);
> > @@ -1587,17 +1590,13 @@ int f2fs_resize_fs(struct f2fs_sb_info *sbi, __u64 block_count)
> > goto out;
> > }
> >
> > - mutex_lock(&sbi->cp_mutex);
> > update_fs_metadata(sbi, -secs);
> > clear_sbi_flag(sbi, SBI_IS_RESIZEFS);
> > set_sbi_flag(sbi, SBI_IS_DIRTY);
> > - mutex_unlock(&sbi->cp_mutex);
> >
> > - err = f2fs_sync_fs(sbi->sb, 1);
> > + err = f2fs_write_checkpoint(sbi, &cpc);
> > if (err) {
> > - mutex_lock(&sbi->cp_mutex);
> > update_fs_metadata(sbi, secs);
> > - mutex_unlock(&sbi->cp_mutex);
> > update_sb_metadata(sbi, secs);
> > f2fs_commit_super(sbi, false);
> > }
> > @@ -1612,7 +1611,8 @@ int f2fs_resize_fs(struct f2fs_sb_info *sbi, __u64 block_count)
> > spin_unlock(&sbi->stat_lock);
> > }
> > clear_sbi_flag(sbi, SBI_IS_RESIZEFS);
> > - mutex_unlock(&sbi->resize_mutex);
> > - thaw_bdev(sbi->sb->s_bdev, sbi->sb);
> > + mutex_unlock(&sbi->cp_mutex);
> > + up_write(&sbi->gc_lock);
> > + thaw_super(sbi->sb);
> > return err;
> > }
> > diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> > index b83b17b54a0a6..1e7b1d21d0177 100644
> > --- a/fs/f2fs/super.c
> > +++ b/fs/f2fs/super.c
> > @@ -3412,7 +3412,6 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
> > init_rwsem(&sbi->gc_lock);
> > mutex_init(&sbi->writepages);
> > mutex_init(&sbi->cp_mutex);
> > - mutex_init(&sbi->resize_mutex);
> > init_rwsem(&sbi->node_write);
> > init_rwsem(&sbi->node_change);
> >
> > diff --git a/include/trace/events/f2fs.h b/include/trace/events/f2fs.h
> > index d97adfc327f03..f5eb03c54e96f 100644
> > --- a/include/trace/events/f2fs.h
> > +++ b/include/trace/events/f2fs.h
> > @@ -50,6 +50,7 @@ TRACE_DEFINE_ENUM(CP_RECOVERY);
> > TRACE_DEFINE_ENUM(CP_DISCARD);
> > TRACE_DEFINE_ENUM(CP_TRIMMED);
> > TRACE_DEFINE_ENUM(CP_PAUSE);
> > +TRACE_DEFINE_ENUM(CP_RESIZE);
> >
> > #define show_block_type(type) \
> > __print_symbolic(type, \
> > @@ -126,7 +127,8 @@ TRACE_DEFINE_ENUM(CP_PAUSE);
> > { CP_RECOVERY, "Recovery" }, \
> > { CP_DISCARD, "Discard" }, \
> > { CP_PAUSE, "Pause" }, \
> > - { CP_TRIMMED, "Trimmed" })
> > + { CP_TRIMMED, "Trimmed" }, \
> > + { CP_RESIZE, "Resize" })
> >
> > #define show_fsync_cpreason(type) \
> > __print_symbolic(type, \
> >
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