linux-kernel - [PATCH 05/12] mm, slub: lower the default slub_max_order with CONFIG_SLUB

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Message-Id: <20221121171202.22080-6-vbabka@suse.cz>
Date:   Mon, 21 Nov 2022 18:11:55 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Pekka Enberg <penberg@...nel.org>
Cc:     Hyeonggon Yoo <42.hyeyoo@...il.com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>, patches@...ts.linux.dev,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Vlastimil Babka <vbabka@...e.cz>
Subject: [PATCH 05/12] mm, slub: lower the default slub_max_order with CONFIG_SLUB_TINY

With CONFIG_SLUB_TINY we want to minimize memory overhead. By lowering
the default slub_max_order we can make slab allocations use smaller
pages. However depending on object sizes, order-0 might not be the best
due to increased fragmentation. When testing on a 8MB RAM k210 system by
Damien Le Moal [1], slub_max_order=1 had the best results, so use that
as the default for CONFIG_SLUB_TINY.

[1] https://lore.kernel.org/all/6a1883c4-4c3f-545a-90e8-2cd805bcf4ae@opensource.wdc.com/

Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
---
 mm/slub.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/slub.c b/mm/slub.c
index 917b79278bad..bf726dd00f7d 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3888,7 +3888,8 @@ EXPORT_SYMBOL(kmem_cache_alloc_bulk);
  * take the list_lock.
  */
 static unsigned int slub_min_order;
-static unsigned int slub_max_order = PAGE_ALLOC_COSTLY_ORDER;
+static unsigned int slub_max_order =
+	IS_ENABLED(CONFIG_SLUB_TINY) ? 1 : PAGE_ALLOC_COSTLY_ORDER;
 static unsigned int slub_min_objects;
 
 /*
-- 
2.38.1