On Tue, 23 Oct 2018 16:43:29 +0000 Roman Gushchin <guro@xxxxxx> 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. > > ... > > --- 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) { > inode->i_state &= ~I_REFERENCED; > spin_unlock(&inode->i_lock); > return LRU_ROTATE; hm, why "1"? I guess one could argue that this will encompass long symlinks, but I just made that up to make "1" appear more justifiable ;)