Re: [PATCH] f2fs: prevent meta updates while checkpoint is in progress

From: Chao Yu
Date: Tue Mar 31 2020 - 23:01:36 EST

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In reply to: Jaegeuk Kim: "Re: [PATCH] f2fs: prevent meta updates while checkpoint is in progress"
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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.

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, \
>

Next message: Chen Zhou: "[PATCH -next] staging: greybus: fix a missing-check bug in gb_lights_light_config()"
Previous message: Nick Terrell: "Re: [PATCH v3 0/8] Add support for ZSTD-compressed kernel and initramfs"
In reply to: Jaegeuk Kim: "Re: [PATCH] f2fs: prevent meta updates while checkpoint is in progress"
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