Re: [PATCH 2/3] sysctl: add support for drop_caches for individual filesystem

[Jan Kara]

On Thu 10-10-24 19:25:42, Ye Bin wrote:
> From: Ye Bin <yebin10@xxxxxxxxxx>
> 
> In order to better analyze the issue of file system uninstallation caused
> by kernel module opening files, it is necessary to perform dentry recycling

I don't quite understand the use case you mention here. Can you explain it
a bit more (that being said I've needed dropping caches for a particular sb
myself a few times for debugging purposes so I generally agree it is a
useful feature).

> on a single file system. But now, apart from global dentry recycling, it is
> not supported to do dentry recycling on a single file system separately.
> This feature has usage scenarios in problem localization scenarios.At the
> same time, it also provides users with a slightly fine-grained
> pagecache/entry recycling mechanism.
> This patch supports the recycling of pagecache/entry for individual file
> systems.
> 
> Signed-off-by: Ye Bin <yebin10@xxxxxxxxxx>
> ---
>  fs/drop_caches.c   | 43 +++++++++++++++++++++++++++++++++++++++++++
>  include/linux/mm.h |  2 ++
>  kernel/sysctl.c    |  9 +++++++++
>  3 files changed, 54 insertions(+)
> 
> diff --git a/fs/drop_caches.c b/fs/drop_caches.c
> index d45ef541d848..99d412cf3e52 100644
> --- a/fs/drop_caches.c
> +++ b/fs/drop_caches.c
> @@ -77,3 +77,46 @@ int drop_caches_sysctl_handler(const struct ctl_table *table, int write,
>  	}
>  	return 0;
>  }
> +
> +int drop_fs_caches_sysctl_handler(const struct ctl_table *table, int write,
> +				  void *buffer, size_t *length, loff_t *ppos)
> +{
> +	unsigned int major, minor;
> +	unsigned int ctl;
> +	struct super_block *sb;
> +	static int stfu;
> +
> +	if (!write)
> +		return 0;
> +
> +	if (sscanf(buffer, "%u:%u:%u", &major, &minor, &ctl) != 3)
> +		return -EINVAL;

I think specifying bdev major & minor number is not a great interface these
days. In particular for filesystems which are not bdev based such as NFS. I
think specifying path to some file/dir in the filesystem is nicer and you
can easily resolve that to sb here as well.

								Honza
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR