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SubjectRe: [PATCH v2 1/7] mm: introduce debugfs interface for kernel memory shrinkers
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Le 22/04/2022 à 22:26, Roman Gushchin a écrit :
> This commit introduces the /sys/kernel/debug/shrinker debugfs
> interface which provides an ability to observe the state and interact
> with individual kernel memory shrinkers.
>
> Because the feature is oriented on kernel developers and 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
> (disabled by default).
>
> This commit introduces "count" and "scan" interfaces for each
> shrinker registered in the system.
>
> Basic usage:
> 1) Get the number of objects
> $ cat count
>
> 2) Try to reclaim 500 objects
> $ echo "500" > scan
>
> Following commits in the series will add memcg- and numa-specific
> features.
>
> 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 | 214 +++++++++++++++++++++++++++++++++++++++
> mm/vmscan.c | 6 +-
> 5 files changed, 246 insertions(+), 3 deletions(-)
> create mode 100644 mm/shrinker_debug.c

[...]

> diff --git a/mm/shrinker_debug.c b/mm/shrinker_debug.c
> new file mode 100644
> index 000000000000..4df7382a0737
> --- /dev/null
> +++ b/mm/shrinker_debug.c

[...]

> +int shrinker_debugfs_add(struct shrinker *shrinker)
> +{
> + struct dentry *entry;
> + char buf[256];
Later, this buffer is filled with a "%s-%d". (patch 5/7)
The %s is generated out of a max 64 bytes long string.

To be consistent with the 2 buffers sizes, maybe this one could be
reduced a bit to save some stack?

CJ

> + int id;
> +
> + lockdep_assert_held(&shrinker_rwsem);
> +
> + /* debugfs isn't initialized yet, add debugfs entries later. */
> + if (!shrinker_debugfs_root)
> + return 0;
> +
> + id = ida_alloc(&shrinker_debugfs_ida, GFP_KERNEL);
> + if (id < 0)
> + return id;
> + shrinker->debugfs_id = id;
> +
> + snprintf(buf, sizeof(buf), "%d", id);
> +
> + /* create debugfs entry */
> + entry = debugfs_create_dir(buf, shrinker_debugfs_root);
> + if (IS_ERR(entry)) {
> + ida_free(&shrinker_debugfs_ida, id);
> + return PTR_ERR(entry);
> + }

[...]

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