linux-kernel - [PATCH] mm/slub: add sanity check for slub_min/max

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Message-Id: <20230920074413.1361547-1-feng.tang@intel.com>
Date:   Wed, 20 Sep 2023 15:44:13 +0800
From:   Feng Tang <feng.tang@...el.com>
To:     Vlastimil Babka <vbabka@...e.cz>, Christoph Lameter <cl@...ux.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Cc:     Feng Tang <feng.tang@...el.com>
Subject: [PATCH] mm/slub: add sanity check for slub_min/max_order cmdline setup

Currently there are 2 parameters could be setup from kernel cmdline:
slub_min_order and slub_max_order. It's possible that the user
configured slub_min_order is bigger than the default slub_max_order
[1], which can still take effect, as calculate_oder() will use MAX_ORDER
as a fallback to check against, but has some downsides:

* the kernel message about SLUB will be strange in showing min/max
  orders:

    SLUB: HWalign=64, Order=9-3, MinObjects=0, CPUs=16, Nodes=1

* in calculate_order() called by each slab, the 2 loops of
  calc_slab_order() will all be meaningless due to slub_min_order
  is bigger than slub_max_order

* prevent future code cleanup like in [2].

Fix it by adding some sanity check to enforce the min/max semantics.

[1]. https://lore.kernel.org/lkml/21a0ba8b-bf05-0799-7c78-2a35f8c8d52a@os.amperecomputing.com/
[2]. https://lore.kernel.org/lkml/20230908145302.30320-7-vbabka@suse.cz/
Signed-off-by: Feng Tang <feng.tang@...el.com>
---
 mm/slub.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/mm/slub.c b/mm/slub.c
index f7940048138c..b36e5eb0ccb7 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -4711,6 +4711,9 @@ static int __init setup_slub_min_order(char *str)
 {
 	get_option(&str, (int *)&slub_min_order);
 
+	if (slub_min_order > slub_max_order)
+		slub_max_order = slub_min_order;
+
 	return 1;
 }
 
@@ -4721,6 +4724,9 @@ static int __init setup_slub_max_order(char *str)
 	get_option(&str, (int *)&slub_max_order);
 	slub_max_order = min_t(unsigned int, slub_max_order, MAX_ORDER);
 
+	if (slub_min_order > slub_max_order)
+		slub_min_order = slub_max_order;
+
 	return 1;
 }
 
-- 
2.27.0