linux-kernel - Re: [PATCH v3 3/6] mm: shrinkers: provide shrinkers with names

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Date:   Mon, 23 May 2022 08:13:41 +1000
From:   Dave Chinner <dchinner@...hat.com>
To:     Roman Gushchin <roman.gushchin@...ux.dev>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Kent Overstreet <kent.overstreet@...il.com>,
        Hillf Danton <hdanton@...a.com>,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>
Subject: Re: [PATCH v3 3/6] mm: shrinkers: provide shrinkers with names

On Mon, May 09, 2022 at 11:38:17AM -0700, Roman Gushchin wrote:
> Currently shrinkers are anonymous objects. For debugging purposes they
> can be identified by count/scan function names, but it's not always
> useful: e.g. for superblock's shrinkers it's nice to have at least
> an idea of to which superblock the shrinker belongs.
> 
> This commit adds names to shrinkers. register_shrinker() and
> prealloc_shrinker() functions are extended to take a format and
> arguments to master a name.
> 
> In some cases it's not possible to determine a good name at the time
> when a shrinker is allocated. For such cases shrinker_debugfs_rename()
> is provided.
> 
> After this change the shrinker debugfs directory looks like:
>   $ cd /sys/kernel/debug/shrinker/
>   $ ls
>     dqcache-16          sb-hugetlbfs-17  sb-rootfs-2      sb-tmpfs-50
>     kfree_rcu-0         sb-hugetlbfs-33  sb-securityfs-6  sb-tracefs-13
>     sb-aio-20           sb-iomem-12      sb-selinuxfs-22  sb-xfs:vda1-36
>     sb-anon_inodefs-15  sb-mqueue-21     sb-sockfs-8      sb-zsmalloc-19
>     sb-bdev-3           sb-nsfs-4        sb-sysfs-26      shadow-18
>     sb-bpf-32           sb-pipefs-14     sb-tmpfs-1       thp_deferred_split-10
>     sb-btrfs:vda2-24    sb-proc-25       sb-tmpfs-27      thp_zero-9
>     sb-cgroup2-30       sb-proc-39       sb-tmpfs-29      xfs_buf-37
>     sb-configfs-23      sb-proc-41       sb-tmpfs-35      xfs_inodegc-38
                                                            ^^^^^^^^^^^^^^

These XFS shrinkers are also per-block device like the superblock.
They need to read like "sb-xfs:vda1-36". and even though it is not
in this list, the xfs dquot shrinker will need this as well.


>     sb-dax-11           sb-proc-45       sb-tmpfs-40      zspool-34
>     sb-debugfs-7        sb-proc-46       sb-tmpfs-42
>     sb-devpts-28        sb-proc-47       sb-tmpfs-43
>     sb-devtmpfs-5       sb-pstore-31     sb-tmpfs-44

The proc and tmpfs shrinkers have the same problem - what instance
do they actually refer to?

> diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> index e1afb9e503e1..5645e92df0c9 100644
> --- a/fs/xfs/xfs_buf.c
> +++ b/fs/xfs/xfs_buf.c
> @@ -1986,7 +1986,7 @@ xfs_alloc_buftarg(
>  	btp->bt_shrinker.scan_objects = xfs_buftarg_shrink_scan;
>  	btp->bt_shrinker.seeks = DEFAULT_SEEKS;
>  	btp->bt_shrinker.flags = SHRINKER_NUMA_AWARE;
> -	if (register_shrinker(&btp->bt_shrinker))
> +	if (register_shrinker(&btp->bt_shrinker, "xfs_buf"))
>  		goto error_pcpu;
>  	return btp;
>  
> diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
> index bffd6eb0b298..d0c4e74ff763 100644
> --- a/fs/xfs/xfs_icache.c
> +++ b/fs/xfs/xfs_icache.c
> @@ -2198,5 +2198,5 @@ xfs_inodegc_register_shrinker(
>  	shrink->flags = SHRINKER_NONSLAB;
>  	shrink->batch = XFS_INODEGC_SHRINKER_BATCH;
>  
> -	return register_shrinker(shrink);
> +	return register_shrinker(shrink, "xfs_inodegc");
>  }
> diff --git a/fs/xfs/xfs_qm.c b/fs/xfs/xfs_qm.c
> index f165d1a3de1d..93ded9e81f49 100644
> --- a/fs/xfs/xfs_qm.c
> +++ b/fs/xfs/xfs_qm.c
> @@ -686,7 +686,7 @@ xfs_qm_init_quotainfo(
>  	qinf->qi_shrinker.seeks = DEFAULT_SEEKS;
>  	qinf->qi_shrinker.flags = SHRINKER_NUMA_AWARE;
>  
> -	error = register_shrinker(&qinf->qi_shrinker);
> +	error = register_shrinker(&qinf->qi_shrinker, "xfs_qm");
>  	if (error)
>  		goto out_free_inos;

Yeah, these all have a xfs_mount passed to them, so the superblock is
easily accessible here (mp->m_super)....

Cheers,

Dave.
-- 
Dave Chinner
dchinner@...hat.com