Re: [PATCH v2] btrfs: add size class stats to sysfs

[Boris Burkov <boris@bur.io>]

On Tue, Feb 07, 2023 at 04:51:01PM +0100, David Sterba wrote:
> On Fri, Jan 27, 2023 at 01:56:50PM -0800, Boris Burkov wrote:
> > Make it possible to see the distribution of size classes for block
> > groups. Helpful for testing and debugging the allocator w.r.t. to size
> > classes.
> > 
> > The new stats can be found at the path:
> > /sys/fs/btrfs/<uid>/allocation/<bg-type>/size_class
> > but they will only be non-zero for bg-type = data.
> > 
> > Signed-off-by: Boris Burkov <boris@bur.io>
> > ---
> > Changelog:
> > v2:
> > - add sysfs path to commit message
> > - unsigned counter types
> > - labeled stat-per-line output format
> > 
> >  fs/btrfs/sysfs.c | 37 +++++++++++++++++++++++++++++++++++++
> >  1 file changed, 37 insertions(+)
> > 
> > diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
> > index 108aa3876186..639f3842f99d 100644
> > --- a/fs/btrfs/sysfs.c
> > +++ b/fs/btrfs/sysfs.c
> > @@ -9,6 +9,7 @@
> >  #include <linux/spinlock.h>
> >  #include <linux/completion.h>
> >  #include <linux/bug.h>
> > +#include <linux/list.h>
> >  #include <crypto/hash.h>
> >  #include "messages.h"
> >  #include "ctree.h"
> > @@ -778,6 +779,40 @@ static ssize_t btrfs_chunk_size_store(struct kobject *kobj,
> >  	return len;
> >  }
> >  
> > +static ssize_t btrfs_size_classes_show(struct kobject *kobj,
> > +				       struct kobj_attribute *a, char *buf)
> > +{
> > +	struct btrfs_space_info *sinfo = to_space_info(kobj);
> > +	struct btrfs_block_group *bg;
> > +	u32 none = 0;
> > +	u32 small = 0;
> > +	u32 medium = 0;
> > +	u32 large = 0;
> > +
> > +	for (int i = 0; i < BTRFS_NR_RAID_TYPES; ++i) {
> > +		list_for_each_entry(bg, &sinfo->block_groups[i], list) {
> 
> Some locking is needed, you can eventually lock only iteration of one
> sinfo and not the whole for cycle. Otherwise looks good.

That sounds like a good way to go to me, as well. Thanks for the review.

> 
> > +			if (!btrfs_block_group_should_use_size_class(bg))
> > +				continue;
> > +			switch (bg->size_class) {
> > +			case BTRFS_BG_SZ_NONE:
> > +				none++;
> > +				break;
> > +			case BTRFS_BG_SZ_SMALL:
> > +				small++;
> > +				break;
> > +			case BTRFS_BG_SZ_MEDIUM:
> > +				medium++;
> > +				break;
> > +			case BTRFS_BG_SZ_LARGE:
> > +				large++;
> > +				break;
> > +			}
> > +		}
> > +	}
> > +	return sysfs_emit(buf, "none %u\nsmall %u\nmedium %u\nlarge %u\n",
> > +			  none, small, medium, large);
> > +}
> > +
> >  #ifdef CONFIG_BTRFS_DEBUG
> >  /*
> >   * Request chunk allocation with current chunk size.
> > @@ -835,6 +870,7 @@ SPACE_INFO_ATTR(bytes_zone_unusable);
> >  SPACE_INFO_ATTR(disk_used);
> >  SPACE_INFO_ATTR(disk_total);
> >  BTRFS_ATTR_RW(space_info, chunk_size, btrfs_chunk_size_show, btrfs_chunk_size_store);
> > +BTRFS_ATTR(space_info, size_classes, btrfs_size_classes_show);
> >  
> >  static ssize_t btrfs_sinfo_bg_reclaim_threshold_show(struct kobject *kobj,
> >  						     struct kobj_attribute *a,
> > @@ -887,6 +923,7 @@ static struct attribute *space_info_attrs[] = {
> >  	BTRFS_ATTR_PTR(space_info, disk_total),
> >  	BTRFS_ATTR_PTR(space_info, bg_reclaim_threshold),
> >  	BTRFS_ATTR_PTR(space_info, chunk_size),
> > +	BTRFS_ATTR_PTR(space_info, size_classes),
> >  #ifdef CONFIG_BTRFS_DEBUG
> >  	BTRFS_ATTR_PTR(space_info, force_chunk_alloc),
> >  #endif
> > -- 
> > 2.38.1