[patch 07/18] mm: don't reclaim inodes with many attached pages

[akpm@linux-foundation.org]

From: Roman Gushchin <guro@fb.com>
Subject: mm: don't reclaim inodes with many attached pages

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.

Link: http://lkml.kernel.org/r/20181023164302.20436-1-guro@fb.com
Signed-off-by: Roman Gushchin <guro@fb.com>
Reported-by: Spock <dairinin@gmail.com>
Tested-by: Spock <dairinin@gmail.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: <stable@vger.kernel.org>	[4.19.x]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---


--- a/fs/inode.c~mm-dont-reclaim-inodes-with-many-attached-pages
+++ a/fs/inode.c
@@ -730,8 +730,11 @@ static enum lru_status inode_lru_isolate
 		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;
_