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

[Roman Gushchin <guro@fb.com>]

On Fri, Oct 26, 2018 at 10:57:35AM +0200, Michal Hocko wrote:
> 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@gmail.com>
> > Signed-off-by: Roman Gushchin <guro@fb.com>
> > Cc: Michal Hocko <mhocko@kernel.org>
> > Cc: Rik van Riel <riel@surriel.com>
> > Cc: Randy Dunlap <rdunlap@infradead.org>
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > ---
> >  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@ ?

No, here many == more than 1.

I'm happy to fix the comment, if you have any suggestions.


Thanks!