linux-kernel - Re: [PATCH v2 5/7] mm: provide shrinkers with names

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Message-ID: <5272f8f0-7624-141b-076c-e8de08e595f5@wanadoo.fr>
Date:   Sat, 23 Apr 2022 09:46:25 +0200
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org
Subject: Re: [PATCH v2 5/7] mm: provide shrinkers with names

Hi,

Le 22/04/2022 à 22:26, Roman Gushchin a écrit :
> 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. If CONFIG_SHRINKER_DEBUG is on,
> the name is saved until the corresponding debugfs object is created,
> otherwise it's simple ignored.
> 
> After this change the shrinker debugfs directory looks like:
>    $ cd /sys/kernel/debug/shrinker/
>    $ ls
>      dqcache-16          sb-cgroup2-30    sb-hugetlbfs-33  sb-proc-41       sb-selinuxfs-22  sb-tmpfs-40    sb-zsmalloc-19
>      kfree_rcu-0         sb-configfs-23   sb-iomem-12      sb-proc-44       sb-sockfs-8      sb-tmpfs-42    shadow-18
>      sb-aio-20           sb-dax-11        sb-mqueue-21     sb-proc-45       sb-sysfs-26      sb-tmpfs-43    thp_deferred_split-10
>      sb-anon_inodefs-15  sb-debugfs-7     sb-nsfs-4        sb-proc-47       sb-tmpfs-1       sb-tmpfs-46    thp_zero-9
>      sb-bdev-3           sb-devpts-28     sb-pipefs-14     sb-pstore-31     sb-tmpfs-27      sb-tmpfs-49    xfs_buf-37
>      sb-bpf-32           sb-devtmpfs-5    sb-proc-25       sb-rootfs-2      sb-tmpfs-29      sb-tracefs-13  xfs_inodegc-38
>      sb-btrfs-24         sb-hugetlbfs-17  sb-proc-39       sb-securityfs-6  sb-tmpfs-35      sb-xfs-36      zspool-34
> 
> Signed-off-by: Roman Gushchin <roman.gushchin@...ux.dev>
> ---

[...]

> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index 59f91e392a2a..1b326b93155c 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -7383,7 +7383,7 @@ static struct r5conf *setup_conf(struct mddev *mddev)
>   	conf->shrinker.count_objects = raid5_cache_count;
>   	conf->shrinker.batch = 128;
>   	conf->shrinker.flags = 0;
> -	if (register_shrinker(&conf->shrinker)) {
> +	if (register_shrinker(&conf->shrinker, "md")) {

Based on pr_warn below, does it make sense to have something like:
   register_shrinker(&conf->shrinker, "md-%s", mdname(mddev))

>   		pr_warn("md/raid:%s: couldn't register shrinker.\n",
>   			mdname(mddev));
>   		goto abort;

[...]

> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 121a54a1602b..6025cfda4932 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -613,7 +613,7 @@ static unsigned long lruvec_lru_size(struct lruvec *lruvec, enum lru_list lru,
>   /*
>    * Add a shrinker callback to be called from the vm.
>    */
> -int prealloc_shrinker(struct shrinker *shrinker)
> +static int __prealloc_shrinker(struct shrinker *shrinker)
>   {
>   	unsigned int size;
>   	int err;
> @@ -637,6 +637,34 @@ int prealloc_shrinker(struct shrinker *shrinker)
>   	return 0;
>   }
>   
> +#ifdef CONFIG_SHRINKER_DEBUG
> +int prealloc_shrinker(struct shrinker *shrinker, const char *fmt, ...)
> +{
> +	int err;
> +	char buf[64];
> +	va_list ap;
> +
> +	va_start(ap, fmt);
> +	vscnprintf(buf, sizeof(buf), fmt, ap);
> +	va_end(ap);
> +
> +	shrinker->name = kstrdup(buf, GFP_KERNEL);
> +	if (!shrinker->name)
> +		return -ENOMEM;

use kvasprintf_const() (and kfree_const() elsewhere) to simplify code 
and take advantage of kstrdup_const() in most cases?

> +
> +	err = __prealloc_shrinker(shrinker);
> +	if (err)
> +		kfree(shrinker->name);
> +
> +	return err;
> +}
> +#else
> +int prealloc_shrinker(struct shrinker *shrinker, const char *fmt, ...)
> +{
> +	return __prealloc_shrinker(shrinker);
> +}
> +#endif
> +
>   void free_prealloced_shrinker(struct shrinker *shrinker)
>   {
>   	if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
> @@ -648,6 +676,9 @@ void free_prealloced_shrinker(struct shrinker *shrinker)
>   
>   	kfree(shrinker->nr_deferred);
>   	shrinker->nr_deferred = NULL;
> +#ifdef CONFIG_SHRINKER_DEBUG
> +	kfree(shrinker->name);
> +#endif
>   }
>   
>   void register_shrinker_prepared(struct shrinker *shrinker)
> @@ -659,15 +690,38 @@ void register_shrinker_prepared(struct shrinker *shrinker)
>   	up_write(&shrinker_rwsem);
>   }
>   
> -int register_shrinker(struct shrinker *shrinker)
> +static int __register_shrinker(struct shrinker *shrinker)
>   {
> -	int err = prealloc_shrinker(shrinker);
> +	int err = __prealloc_shrinker(shrinker);
>   
>   	if (err)
>   		return err;
>   	register_shrinker_prepared(shrinker);
>   	return 0;
>   }
> +
> +#ifdef CONFIG_SHRINKER_DEBUG
> +int register_shrinker(struct shrinker *shrinker, const char *fmt, ...)
> +{
> +	char buf[64];
> +	va_list ap;
> +
> +	va_start(ap, fmt);
> +	vscnprintf(buf, sizeof(buf), fmt, ap);
> +	va_end(ap);
> +
> +	shrinker->name = kstrdup(buf, GFP_KERNEL);
> +	if (!shrinker->name)
> +		return -ENOMEM;
> +

same as above.

> +	return __register_shrinker(shrinker);

Missing error handling and freeing of shrinker->name as done in 
prealloc_shrinker()?

CJ

> +}
> +#else
> +int register_shrinker(struct shrinker *shrinker, const char *fmt, ...)
> +{
> +	return __register_shrinker(shrinker);
> +}
> +#endif
>   EXPORT_SYMBOL(register_shrinker);
>   
>   /*

[...]