Re: [RFC PATCH] mm: don't reclaim inodes with many attached pages

[Michal Hocko]

Spock doesn't seem to be cced here - fixed now

On Tue 23-10-18 16:43:29, Roman Gushchin wrote:
> Spock reported that the commit 172b06c32b94 ("mm: slowly shrink slabs
> with a relatively small number of objects") leads to a regression on
> his setup: periodically the majority of the pagecache is evicted
> without an obvious reason, while before the change the amount of free
> memory was balancing around the watermark.
> 
> The reason behind is that the mentioned above change created some
> minimal background pressure on the inode cache. The problem is that
> if an inode is considered to be reclaimed, all belonging pagecache
> page are stripped, no matter how many of them are there. So, if a huge
> multi-gigabyte file is cached in the memory, and the goal is to
> reclaim only few slab objects (unused inodes), we still can eventually
> evict all gigabytes of the pagecache at once.
> 
> The workload described by Spock has few large non-mapped files in the
> pagecache, so it's especially noticeable.
> 
> To solve the problem let's postpone the reclaim of inodes, which have
> more than 1 attached page. Let's wait until the pagecache pages will
> be evicted naturally by scanning the corresponding LRU lists, and only
> then reclaim the inode structure.

Has this actually fixed/worked around the issue?

> Reported-by: Spock <dairinin@xxxxxxxxx>
> Signed-off-by: Roman Gushchin <guro@xxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
> Cc: Rik van Riel <riel@xxxxxxxxxxx>
> Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> ---
>  fs/inode.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/inode.c b/fs/inode.c
> index 73432e64f874..0cd47fe0dbe5 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -730,8 +730,11 @@ static enum lru_status inode_lru_isolate(struct list_head *item,
>  		return LRU_REMOVED;
>  	}
>  
> -	/* recently referenced inodes get one more pass */
> -	if (inode->i_state & I_REFERENCED) {
> +	/*
> +	 * Recently referenced inodes and inodes with many attached pages
> +	 * get one more pass.
> +	 */
> +	if (inode->i_state & I_REFERENCED || inode->i_data.nrpages > 1) {

The comment is just confusing. Did you mean to say s@many@any@ ?

>  		inode->i_state &= ~I_REFERENCED;
>  		spin_unlock(&inode->i_lock);
>  		return LRU_ROTATE;
> -- 
> 2.17.2

-- 
Michal Hocko
SUSE Labs