linux-kernel - [PATCH] percpu/module resevation: change resevation size iff X86

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Date:   Mon, 21 Jan 2019 13:47:31 +0200
From:   Eial Czerwacki <eial@...lemp.com>
To:     linux-kernel@...r.kernel.org
Cc:     Eial Czerwacki <eial@...lemp.com>,
        Shai Fultheim <shai@...lemp.com>, Oren Twaig <oren@...lemp.com>
Subject: [PATCH] percpu/module resevation: change resevation size iff X86_VSMP is set

as reported in bug #201339 (https://bugzilla.kernel.org/show_bug.cgi?id=201339)
by enabling X86_VSMP, INTERNODE_CACHE_BYTES's definition differs from the default one
causing the struct size to exceed the size ok 8KB.

in order to avoid such issue, increse PERCPU_MODULE_RESERVE to 64KB if CONFIG_X86_VSMP is set.

the value was caculated on linux 4.20.3, make allmodconfig all and the following oneliner:
for f in `find -name *.ko`; do echo $f; readelf -S $f  |grep perc; done |grep data..percpu -B 1 |grep ko |while read r; do echo -n "$r: "; objdump --syms --section=.data..percpu $r|grep data |sort -n  |awk '{c++; d=strtonum("0x" $1) + strtonum("0x" $5); if (m < d) m = d;} END {printf("%d vars-> last addr 0x%x ( %d )\n", c, m, m)}' ; done |column -t |sort -k 8 -n | awk '{print $8}'| paste -sd+ | bc

Signed-off-by: Eial Czerwacki <eial@...lemp.com>
Signed-off-by: Shai Fultheim <shai@...lemp.com>
Signed-off-by: Oren Twaig <oren@...lemp.com>
---
 include/linux/percpu.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/include/linux/percpu.h b/include/linux/percpu.h
index 70b7123..6b79693 100644
--- a/include/linux/percpu.h
+++ b/include/linux/percpu.h
@@ -14,7 +14,11 @@
 
 /* enough to cover all DEFINE_PER_CPUs in modules */
 #ifdef CONFIG_MODULES
+#ifdef X86_VSMP
+#define PERCPU_MODULE_RESERVE		(1 << 16)
+#else
 #define PERCPU_MODULE_RESERVE		(8 << 10)
+#endif
 #else
 #define PERCPU_MODULE_RESERVE		0
 #endif
-- 
2.7.4