Re: [PATCH 1/3] vfs: introduce shrink_icache_sb() helper

[Jan Kara <jack@suse.cz>]

On Thu 10-10-24 19:25:41, Ye Bin wrote:
> From: Ye Bin <yebin10@huawei.com>
> 
> This patch is prepare for support drop_caches for specify file system.
> shrink_icache_sb() helper walk the superblock inode LRU for freeable inodes
> and attempt to free them.
> 
> Signed-off-by: Ye Bin <yebin10@huawei.com>
> ---
>  fs/inode.c    | 17 +++++++++++++++++
>  fs/internal.h |  1 +
>  2 files changed, 18 insertions(+)
> 
> diff --git a/fs/inode.c b/fs/inode.c
> index 1939f711d2c9..2129b48571b4 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -1045,6 +1045,23 @@ long prune_icache_sb(struct super_block *sb, struct shrink_control *sc)
>  	return freed;
>  }
>  
> +/*
> + * Walk the superblock inode LRU for freeable inodes and attempt to free them.
> + * Inodes to be freed are moved to a temporary list and then are freed outside
> + * inode_lock by dispose_list().
> + */
> +void shrink_icache_sb(struct super_block *sb)
> +{
> +	do {
> +		LIST_HEAD(dispose);
> +
> +		list_lru_walk(&sb->s_inode_lru, inode_lru_isolate,
> +			      &dispose, 1024);
> +		dispose_list(&dispose);
> +	} while (list_lru_count(&sb->s_inode_lru) > 0);
> +}
> +EXPORT_SYMBOL(shrink_icache_sb);

Hum, but this will livelock if we cannot remove all the inodes? Now I guess
inode_lru_isolate() usually removes busy inodes from the LRU so this should
not happen in practice but such behavior is not guaranteed (we can LRU_SKIP
inodes if i_lock is busy or LRU_RETRY if inode has page cache pages). So I
think we need some safety net here...

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR