Re: [PATCH v4] f2fs: add sysfs nodes to get runtime compression stat

[Daeho Jeong]

Thanks for suggesting me sysfs_emit().

For atomic values, actually, those are needed for writer part, not reader.

+#define add_compr_block_stat(inode, blocks)                            \
+       do {                                                            \
+               struct f2fs_sb_info *sbi = F2FS_I_SB(inode);            \
+               int diff = F2FS_I(inode)->i_cluster_size - blocks;      \
+               atomic64_add(blocks, &sbi->compr_written_block);        \
+               atomic64_add(diff, &sbi->compr_saved_block);            \
+       } while (0)

I needed a protection here, because they might be updated in the race condition.

2021년 3월 12일 (금) 오후 9:39, Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx>님이 작성:
>
> On Fri, Mar 12, 2021 at 09:25:31PM +0900, Daeho Jeong wrote:
> > From: Daeho Jeong <daehojeong@xxxxxxxxxx>
> >
> > I've added new sysfs nodes to show runtime compression stat since mount.
> > compr_written_block - show the block count written after compression
> > compr_saved_block - show the saved block count with compression
> > compr_new_inode - show the count of inode newly enabled for compression
> >
> > Signed-off-by: Daeho Jeong <daehojeong@xxxxxxxxxx>
> > ---
> > v2: thanks to kernel test robot <lkp@xxxxxxxxx>, fixed compile issue
> >     related to kernel config
> > v3: changed sysfs nodes' names and made them runtime stat, not
> >     persistent on disk
> > v4: changed sysfs nodes' desctiption
> > ---
> >  Documentation/ABI/testing/sysfs-fs-f2fs | 24 ++++++++++
> >  fs/f2fs/compress.c                      |  1 +
> >  fs/f2fs/f2fs.h                          | 19 ++++++++
> >  fs/f2fs/super.c                         |  7 +++
> >  fs/f2fs/sysfs.c                         | 58 +++++++++++++++++++++++++
> >  5 files changed, 109 insertions(+)
> >
> > diff --git a/Documentation/ABI/testing/sysfs-fs-f2fs b/Documentation/ABI/testing/sysfs-fs-f2fs
> > index cbeac1bebe2f..ddd4bd6116fc 100644
> > --- a/Documentation/ABI/testing/sysfs-fs-f2fs
> > +++ b/Documentation/ABI/testing/sysfs-fs-f2fs
> > @@ -409,3 +409,27 @@ Description:     Give a way to change checkpoint merge daemon's io priority.
> >               I/O priority "3". We can select the class between "rt" and "be",
> >               and set the I/O priority within valid range of it. "," delimiter
> >               is necessary in between I/O class and priority number.
> > +
> > +What:                /sys/fs/f2fs/<disk>/compr_written_block
> > +Date:                March 2021
> > +Contact:     "Daeho Jeong" <daehojeong@xxxxxxxxxx>
> > +Description: Show the block count written after compression since mount. Note
> > +             that when the compressed blocks are deleted, this count doesn't
> > +             decrease. If you write "0" here, you can initialize
> > +             compr_written_block and compr_saved_block to "0".
> > +
> > +What:                /sys/fs/f2fs/<disk>/compr_saved_block
> > +Date:                March 2021
> > +Contact:     "Daeho Jeong" <daehojeong@xxxxxxxxxx>
> > +Description: Show the saved block count with compression since mount. Note
> > +             that when the compressed blocks are deleted, this count doesn't
> > +             decrease. If you write "0" here, you can initialize
> > +             compr_written_block and compr_saved_block to "0".
> > +
> > +What:                /sys/fs/f2fs/<disk>/compr_new_inode
> > +Date:                March 2021
> > +Contact:     "Daeho Jeong" <daehojeong@xxxxxxxxxx>
> > +Description: Show the count of inode newly enabled for compression since mount.
> > +             Note that when the compression is disabled for the files, this count
> > +             doesn't decrease. If you write "0" here, you can initialize
> > +             compr_new_inode to "0".
> > diff --git a/fs/f2fs/compress.c b/fs/f2fs/compress.c
> > index 77fa342de38f..3c9d797dbdd6 100644
> > --- a/fs/f2fs/compress.c
> > +++ b/fs/f2fs/compress.c
> > @@ -1353,6 +1353,7 @@ static int f2fs_write_compressed_pages(struct compress_ctx *cc,
> >       if (fio.compr_blocks)
> >               f2fs_i_compr_blocks_update(inode, fio.compr_blocks - 1, false);
> >       f2fs_i_compr_blocks_update(inode, cc->nr_cpages, true);
> > +     add_compr_block_stat(inode, cc->nr_cpages);
> >
> >       set_inode_flag(cc->inode, FI_APPEND_WRITE);
> >       if (cc->cluster_idx == 0)
> > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> > index e2d302ae3a46..2c989f8caf05 100644
> > --- a/fs/f2fs/f2fs.h
> > +++ b/fs/f2fs/f2fs.h
> > @@ -1623,6 +1623,11 @@ struct f2fs_sb_info {
> >  #ifdef CONFIG_F2FS_FS_COMPRESSION
> >       struct kmem_cache *page_array_slab;     /* page array entry */
> >       unsigned int page_array_slab_size;      /* default page array slab size */
> > +
> > +     /* For runtime compression statistics */
> > +     atomic64_t compr_written_block;
> > +     atomic64_t compr_saved_block;
> > +     atomic_t compr_new_inode;
>
> Why do you need these to be atomic?  What requires this?
>
> > +#ifdef CONFIG_F2FS_FS_COMPRESSION
> > +     if (!strcmp(a->attr.name, "compr_written_block")) {
> > +             u64 bcount;
> > +             int len;
> > +
> > +             bcount = atomic64_read(&sbi->compr_written_block);
> > +
> > +             len = scnprintf(buf, PAGE_SIZE, "%llu\n", bcount);
>
> Please use sysfs_emit() for new sysfs entries like these.  Makes it much
> simpler.
>
> And look, you really do not need an atomic value as this is just a
> random number you are sending to userspace that could be stale the
> minute you read from it.
>
> Please just use a normal u64 and save the cpu sync for stuff like this.
>
> thanks,
>
> greg k-h