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SubjectRe: [PATCH v3 2/6] mm: shrinkers: introduce debugfs interface for memory shrinkers
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Le 09/05/2022 à 20:38, Roman Gushchin a écrit :
> This commit introduces the /sys/kernel/debug/shrinker debugfs
> interface which provides an ability to observe the state of
> individual kernel memory shrinkers.
>
> Because the feature adds some memory overhead (which shouldn't be
> large unless there is a huge amount of registered shrinkers), it's
> guarded by a config option (enabled by default).
>
> This commit introduces the "count" interface for each shrinker
> registered in the system.
>
> The output is in the following format:
> <cgroup inode id> <nr of objects on node 0> <nr of objects on node 1>...
> <cgroup inode id> <nr of objects on node 0> <nr of objects on node 1>...
> ...
>
> To reduce the size of output on machines with many thousands cgroups,
> if the total number of objects on all nodes is 0, the line is omitted.
>
> If the shrinker is not memcg-aware or CONFIG_MEMCG is off, 0 is
> printed as cgroup inode id. If the shrinker is not numa-aware, 0's are
> printed for all nodes except the first one.
>
> This commit gives debugfs entries simple numeric names, which are not
> very convenient. The following commit in the series will provide
> shrinkers with more meaningful names.
>
> Signed-off-by: Roman Gushchin <roman.gushchin@linux.dev>
> ---
> include/linux/shrinker.h | 19 ++++-
> lib/Kconfig.debug | 9 +++
> mm/Makefile | 1 +
> mm/shrinker_debug.c | 171 +++++++++++++++++++++++++++++++++++++++
> mm/vmscan.c | 6 +-
> 5 files changed, 203 insertions(+), 3 deletions(-)
> create mode 100644 mm/shrinker_debug.c
>
> diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
> index 76fbf92b04d9..2ced8149c513 100644
> --- a/include/linux/shrinker.h
> +++ b/include/linux/shrinker.h
> @@ -72,6 +72,10 @@ struct shrinker {
> #ifdef CONFIG_MEMCG
> /* ID in shrinker_idr */
> int id;
> +#endif
> +#ifdef CONFIG_SHRINKER_DEBUG
> + int debugfs_id;
> + struct dentry *debugfs_entry;
> #endif
> /* objs pending delete, per node */
> atomic_long_t *nr_deferred;
> @@ -94,4 +98,17 @@ extern int register_shrinker(struct shrinker *shrinker);
> extern void unregister_shrinker(struct shrinker *shrinker);
> extern void free_prealloced_shrinker(struct shrinker *shrinker);
> extern void synchronize_shrinkers(void);
> -#endif
> +
> +#ifdef CONFIG_SHRINKER_DEBUG
> +extern int shrinker_debugfs_add(struct shrinker *shrinker);
> +extern void shrinker_debugfs_remove(struct shrinker *shrinker);
> +#else /* CONFIG_SHRINKER_DEBUG */
> +static inline int shrinker_debugfs_add(struct shrinker *shrinker)
> +{
> + return 0;
> +}
> +static inline void shrinker_debugfs_remove(struct shrinker *shrinker)
> +{
> +}
> +#endif /* CONFIG_SHRINKER_DEBUG */
> +#endif /* _LINUX_SHRINKER_H */
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 3fd7a2e9eaf1..5fa65a649798 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -733,6 +733,15 @@ config SLUB_STATS
> out which slabs are relevant to a particular load.
> Try running: slabinfo -DA
>
> +config SHRINKER_DEBUG
> + default y

The previous version of the serie had default 'n'.
Is it intentional to have it now activated by default? It looked more
like a tuning functionality when fine grained mangement of shrinker is
needed.


> + bool "Enable shrinker debugging support"
> + depends on DEBUG_FS
> + help
> + Say Y to enable the shrinker debugfs interface which provides
> + visibility into the kernel memory shrinkers subsystem.
> + Disable it to avoid an extra memory footprint.
> +

[...]

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