The patch titled
Subject: mm: make minimum slab alignment a runtime property
has been added to the -mm tree. Its filename is
mm-make-minimum-slab-alignment-a-runtime-property.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-make-minimum-slab-alignment-a-runtime-property.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-make-minimum-slab-alignment-a-runtime-property.patch
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
From: Peter Collingbourne <pcc@xxxxxxxxxx>
Subject: mm: make minimum slab alignment a runtime property
When CONFIG_KASAN_HW_TAGS is enabled we currently increase the minimum
slab alignment to 16. This happens even if MTE is not supported in
hardware or disabled via kasan=off, which creates an unnecessary memory
overhead in those cases. Eliminate this overhead by making the minimum
slab alignment a runtime property and only aligning to 16 if KASAN is
enabled at runtime.
On a DragonBoard 845c (non-MTE hardware) with a kernel built with
CONFIG_KASAN_HW_TAGS, waiting for quiescence after a full Android boot I
see the following Slab measurements in /proc/meminfo (median of 3
reboots):
Before: 169020 kB
After: 167304 kB
Link: https://linux-review.googlesource.com/id/I752e725179b43b144153f4b6f584ceb646473ead
Link: https://lkml.kernel.org/r/20220427195820.1716975-2-pcc@xxxxxxxxxx
Signed-off-by: Peter Collingbourne <pcc@xxxxxxxxxx>
Reviewed-by: Andrey Konovalov <andreyknvl@xxxxxxxxx>
Reviewed-by: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>
Tested-by: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>
Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Cc: Andrey Ryabinin <ryabinin.a.a@xxxxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
arch/arm64/include/asm/cache.h | 17 ++++++++++++-----
include/linux/slab.h | 12 ++++++++++++
mm/slab.c | 7 +++----
mm/slab_common.c | 3 +--
mm/slob.c | 6 +++---
5 files changed, 31 insertions(+), 14 deletions(-)
--- a/arch/arm64/include/asm/cache.h~mm-make-minimum-slab-alignment-a-runtime-property
+++ a/arch/arm64/include/asm/cache.h
@@ -6,6 +6,7 @@
#define __ASM_CACHE_H
#include <asm/cputype.h>
+#include <asm/mte-def.h>
#define CTR_L1IP_SHIFT 14
#define CTR_L1IP_MASK 3
@@ -49,16 +50,22 @@
*/
#define ARCH_DMA_MINALIGN (128)
+#ifndef __ASSEMBLY__
+
+#include <linux/bitops.h>
+#include <linux/kasan-enabled.h>
+
#ifdef CONFIG_KASAN_SW_TAGS
#define ARCH_SLAB_MINALIGN (1ULL << KASAN_SHADOW_SCALE_SHIFT)
#elif defined(CONFIG_KASAN_HW_TAGS)
-#define ARCH_SLAB_MINALIGN MTE_GRANULE_SIZE
+static inline size_t arch_slab_minalign(void)
+{
+ return kasan_hw_tags_enabled() ? MTE_GRANULE_SIZE :
+ __alignof__(unsigned long long);
+}
+#define arch_slab_minalign() arch_slab_minalign()
#endif
-#ifndef __ASSEMBLY__
-
-#include <linux/bitops.h>
-
#define ICACHEF_ALIASING 0
#define ICACHEF_VPIPT 1
extern unsigned long __icache_flags;
--- a/include/linux/slab.h~mm-make-minimum-slab-alignment-a-runtime-property
+++ a/include/linux/slab.h
@@ -210,6 +210,18 @@ void kmem_dump_obj(void *object);
#endif
/*
+ * Arches can define this function if they want to decide the minimum slab
+ * alignment at runtime. The value returned by the function must be a power
+ * of two and >= ARCH_SLAB_MINALIGN.
+ */
+#ifndef arch_slab_minalign
+static inline size_t arch_slab_minalign(void)
+{
+ return ARCH_SLAB_MINALIGN;
+}
+#endif
+
+/*
* kmalloc and friends return ARCH_KMALLOC_MINALIGN aligned
* pointers. kmem_cache_alloc and friends return ARCH_SLAB_MINALIGN
* aligned pointers.
--- a/mm/slab.c~mm-make-minimum-slab-alignment-a-runtime-property
+++ a/mm/slab.c
@@ -3009,10 +3009,9 @@ static void *cache_alloc_debugcheck_afte
objp += obj_offset(cachep);
if (cachep->ctor && cachep->flags & SLAB_POISON)
cachep->ctor(objp);
- if (ARCH_SLAB_MINALIGN &&
- ((unsigned long)objp & (ARCH_SLAB_MINALIGN-1))) {
- pr_err("0x%px: not aligned to ARCH_SLAB_MINALIGN=%d\n",
- objp, (int)ARCH_SLAB_MINALIGN);
+ if ((unsigned long)objp & (arch_slab_minalign() - 1)) {
+ pr_err("0x%px: not aligned to arch_slab_minalign()=%d\n", objp,
+ (int)arch_slab_minalign());
}
return objp;
}
--- a/mm/slab_common.c~mm-make-minimum-slab-alignment-a-runtime-property
+++ a/mm/slab_common.c
@@ -154,8 +154,7 @@ static unsigned int calculate_alignment(
align = max(align, ralign);
}
- if (align < ARCH_SLAB_MINALIGN)
- align = ARCH_SLAB_MINALIGN;
+ align = max_t(size_t, align, arch_slab_minalign());
return ALIGN(align, sizeof(void *));
}
--- a/mm/slob.c~mm-make-minimum-slab-alignment-a-runtime-property
+++ a/mm/slob.c
@@ -478,7 +478,7 @@ static __always_inline void *
__do_kmalloc_node(size_t size, gfp_t gfp, int node, unsigned long caller)
{
unsigned int *m;
- int minalign = max_t(size_t, ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
+ int minalign = max_t(size_t, ARCH_KMALLOC_MINALIGN, arch_slab_minalign());
void *ret;
gfp &= gfp_allowed_mask;
@@ -555,7 +555,7 @@ void kfree(const void *block)
sp = virt_to_folio(block);
if (folio_test_slab(sp)) {
- int align = max_t(size_t, ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
+ int align = max_t(size_t, ARCH_KMALLOC_MINALIGN, arch_slab_minalign());
unsigned int *m = (unsigned int *)(block - align);
slob_free(m, *m + align);
} else {
@@ -584,7 +584,7 @@ size_t __ksize(const void *block)
if (unlikely(!folio_test_slab(folio)))
return folio_size(folio);
- align = max_t(size_t, ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
+ align = max_t(size_t, ARCH_KMALLOC_MINALIGN, arch_slab_minalign());
m = (unsigned int *)(block - align);
return SLOB_UNITS(*m) * SLOB_UNIT;
}
_
Patches currently in -mm which might be from pcc@xxxxxxxxxx are
printk-stop-including-cacheh-from-printkh.patch
mm-make-minimum-slab-alignment-a-runtime-property.patch
