linux-kernel - [PATCH 2/2] Revert "mm: slowly shrink slabs with a relatively small number of objects"

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Message-Id: <20190130041707.27750-3-david@fromorbit.com>
Date:   Wed, 30 Jan 2019 15:17:07 +1100
From:   Dave Chinner <david@...morbit.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-xfs@...r.kernel.org
Cc:     guro@...com, akpm@...ux-foundation.org, mhocko@...nel.org,
        vdavydov.dev@...il.com
Subject: [PATCH 2/2] Revert "mm: slowly shrink slabs with a relatively small number of objects"

From: Dave Chinner <dchinner@...hat.com>

This reverts commit 172b06c32b949759fe6313abec514bc4f15014f4.

This change changes the agressiveness of shrinker reclaim, causing
small cache and low priority reclaim to greatly increase
scanning pressure on small caches. As a result, light memory
pressure has a disproportionate affect on small caches, and causes
large caches to be reclaimed much faster than previously.

As a result, it greatly perturbs the delicate balance of the VFS
caches (dentry/inode vs file page cache) such that the inode/dentry
caches are reclaimed much, much faster than the page cache and this
drives us into several other caching imbalance related problems.

As such, this is a bad change and needs to be reverted.

[ Needs some massaging to retain the later seekless shrinker
modifications. ]

cc: <stable@...r.kernel.org>
Signed-off-by: Dave Chinner <dchinner@...hat.com>
---
 mm/vmscan.c | 10 ----------
 1 file changed, 10 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index a714c4f800e9..e979705bbf32 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -491,16 +491,6 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
 		delta = freeable / 2;
 	}

-	/*
-	 * Make sure we apply some minimal pressure on default priority
-	 * even on small cgroups. Stale objects are not only consuming memory
-	 * by themselves, but can also hold a reference to a dying cgroup,
-	 * preventing it from being reclaimed. A dying cgroup with all
-	 * corresponding structures like per-cpu stats and kmem caches
-	 * can be really big, so it may lead to a significant waste of memory.
-	 */
-	delta = max_t(unsigned long long, delta, min(freeable, batch_size));
-
 	total_scan += delta;
 	if (total_scan < 0) {
 		pr_err("shrink_slab: %pF negative objects to delete nr=%ld\n",
-- 
2.20.1