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Date: Wed, 27 Apr 2022 17:25:18 -0700
From: Roman Gushchin <roman.gushchin@...ux.dev>
To: Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
Dave Chinner <dchinner@...hat.com>,
linux-kernel@...r.kernel.org, Yang Shi <shy828301@...il.com>,
Kent Overstreet <kent.overstreet@...il.com>,
Hillf Danton <hdanton@...a.com>
Subject: Re: [PATCH v2 5/7] mm: provide shrinkers with names
On Sat, Apr 23, 2022 at 09:46:25AM +0200, Christophe JAILLET wrote:
> 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;
Good idea, will do, thanks!
>
> [...]
>
> > 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?
Sure, good point.
>
> > +
> > + 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()?
Will check in the next version.
Thank you for taking a look!
Roman
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