On Wed, Apr 20, 2022 at 08:17:38PM -0700, Peter Collingbourne wrote: > 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 > Signed-off-by: Peter Collingbourne <pcc@xxxxxxxxxx> > --- > arch/arc/include/asm/cache.h | 4 ++-- > arch/arm/include/asm/cache.h | 2 +- > arch/arm64/include/asm/cache.h | 19 +++++++++++++------ > arch/microblaze/include/asm/page.h | 2 +- > arch/riscv/include/asm/cache.h | 2 +- > arch/sparc/include/asm/cache.h | 2 +- > arch/xtensa/include/asm/processor.h | 2 +- > fs/binfmt_flat.c | 9 ++++++--- > include/crypto/hash.h | 2 +- > include/linux/slab.h | 22 +++++++++++++++++----- > mm/slab.c | 7 +++---- > mm/slab_common.c | 3 +-- > mm/slob.c | 6 +++--- > 13 files changed, 51 insertions(+), 31 deletions(-) [+Cc slab people, Catalin and affected subsystems' folks] just FYI, There is similar discussion about kmalloc caches' alignment. https://lore.kernel.org/linux-mm/20220405135758.774016-1-catalin.marinas@xxxxxxx/ It seems this is another demand for runtime resolution of slab alignment, But slightly different from kmalloc as there is no requirement for DMA alignment. > > diff --git a/arch/arc/include/asm/cache.h b/arch/arc/include/asm/cache.h > index f0f1fc5d62b6..b6a7763fd5d6 100644 > --- a/arch/arc/include/asm/cache.h > +++ b/arch/arc/include/asm/cache.h > @@ -55,11 +55,11 @@ > * Make sure slab-allocated buffers are 64-bit aligned when atomic64_t uses > * ARCv2 64-bit atomics (LLOCKD/SCONDD). This guarantess runtime 64-bit > * alignment for any atomic64_t embedded in buffer. > - * Default ARCH_SLAB_MINALIGN is __alignof__(long long) which has a relaxed > + * Default ARCH_SLAB_MIN_MINALIGN is __alignof__(long long) which has a relaxed > * value of 4 (and not 8) in ARC ABI. > */ > #if defined(CONFIG_ARC_HAS_LL64) && defined(CONFIG_ARC_HAS_LLSC) > -#define ARCH_SLAB_MINALIGN 8 > +#define ARCH_SLAB_MIN_MINALIGN 8 > #endif > Why isn't it just ARCH_SLAB_MINALIGN? > extern int ioc_enable; > diff --git a/arch/arm/include/asm/cache.h b/arch/arm/include/asm/cache.h > index e3ea34558ada..3e1018bb9805 100644 > --- a/arch/arm/include/asm/cache.h > +++ b/arch/arm/include/asm/cache.h > @@ -21,7 +21,7 @@ > * With EABI on ARMv5 and above we must have 64-bit aligned slab pointers. > */ > #if defined(CONFIG_AEABI) && (__LINUX_ARM_ARCH__ >= 5) > -#define ARCH_SLAB_MINALIGN 8 > +#define ARCH_SLAB_MIN_MINALIGN 8 > #endif > > #define __read_mostly __section(".data..read_mostly") > diff --git a/arch/arm64/include/asm/cache.h b/arch/arm64/include/asm/cache.h > index a074459f8f2f..38f171591c3f 100644 > --- a/arch/arm64/include/asm/cache.h > +++ b/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 > @@ -49,15 +50,21 @@ > */ > #define ARCH_DMA_MINALIGN (128) > > -#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 > -#endif > - > #ifndef __ASSEMBLY__ > > #include <linux/bitops.h> > +#include <linux/kasan-enabled.h> > + > +#ifdef CONFIG_KASAN_SW_TAGS > +#define ARCH_SLAB_MIN_MINALIGN (1ULL << KASAN_SHADOW_SCALE_SHIFT) > +#elif defined(CONFIG_KASAN_HW_TAGS) > +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 > kasan_hw_tags_enabled() is also false when kasan is just not initialized yet. What about writing a new helper something like kasan_is_disabled() instead? > #define ICACHEF_ALIASING 0 > #define ICACHEF_VPIPT 1 > diff --git a/arch/microblaze/include/asm/page.h b/arch/microblaze/include/asm/page.h > index 4b8b2fa78fc5..ccdbc1da3c3e 100644 > --- a/arch/microblaze/include/asm/page.h > +++ b/arch/microblaze/include/asm/page.h > @@ -33,7 +33,7 @@ > /* MS be sure that SLAB allocates aligned objects */ > #define ARCH_DMA_MINALIGN L1_CACHE_BYTES > > -#define ARCH_SLAB_MINALIGN L1_CACHE_BYTES > +#define ARCH_SLAB_MIN_MINALIGN L1_CACHE_BYTES > > /* > * PAGE_OFFSET -- the first address of the first page of memory. With MMU > diff --git a/arch/riscv/include/asm/cache.h b/arch/riscv/include/asm/cache.h > index 9b58b104559e..7beb3b5d27c7 100644 > --- a/arch/riscv/include/asm/cache.h > +++ b/arch/riscv/include/asm/cache.h > @@ -16,7 +16,7 @@ > * the flat loader aligns it accordingly. > */ > #ifndef CONFIG_MMU > -#define ARCH_SLAB_MINALIGN 16 > +#define ARCH_SLAB_MIN_MINALIGN 16 > #endif > > #endif /* _ASM_RISCV_CACHE_H */ > diff --git a/arch/sparc/include/asm/cache.h b/arch/sparc/include/asm/cache.h > index e62fd0e72606..9d8cb4687b7e 100644 > --- a/arch/sparc/include/asm/cache.h > +++ b/arch/sparc/include/asm/cache.h > @@ -8,7 +8,7 @@ > #ifndef _SPARC_CACHE_H > #define _SPARC_CACHE_H > > -#define ARCH_SLAB_MINALIGN __alignof__(unsigned long long) > +#define ARCH_SLAB_MIN_MINALIGN __alignof__(unsigned long long) > > #define L1_CACHE_SHIFT 5 > #define L1_CACHE_BYTES 32 > diff --git a/arch/xtensa/include/asm/processor.h b/arch/xtensa/include/asm/processor.h > index 4489a27d527a..e3ea278e3fcf 100644 > --- a/arch/xtensa/include/asm/processor.h > +++ b/arch/xtensa/include/asm/processor.h > @@ -18,7 +18,7 @@ > #include <asm/types.h> > #include <asm/regs.h> > > -#define ARCH_SLAB_MINALIGN XTENSA_STACK_ALIGNMENT > +#define ARCH_SLAB_MIN_MINALIGN XTENSA_STACK_ALIGNMENT > > /* > * User space process size: 1 GB. > diff --git a/fs/binfmt_flat.c b/fs/binfmt_flat.c > index 626898150011..8ff1bf7d1e87 100644 > --- a/fs/binfmt_flat.c > +++ b/fs/binfmt_flat.c > @@ -64,7 +64,10 @@ > * Here we can be a bit looser than the data sections since this > * needs to only meet arch ABI requirements. > */ > -#define FLAT_STACK_ALIGN max_t(unsigned long, sizeof(void *), ARCH_SLAB_MINALIGN) > +static size_t flat_stack_align(void) > +{ > + return max_t(unsigned long, sizeof(void *), arch_slab_minalign()); > +} > > #define RELOC_FAILED 0xff00ff01 /* Relocation incorrect somewhere */ > #define UNLOADED_LIB 0x7ff000ff /* Placeholder for unused library */ > @@ -148,7 +151,7 @@ static int create_flat_tables(struct linux_binprm *bprm, unsigned long arg_start > sp -= 2; /* argvp + envp */ > sp -= 1; /* &argc */ > > - current->mm->start_stack = (unsigned long)sp & -FLAT_STACK_ALIGN; > + current->mm->start_stack = (unsigned long)sp & -flat_stack_align(); > sp = (unsigned long __user *)current->mm->start_stack; > > if (put_user(bprm->argc, sp++)) > @@ -966,7 +969,7 @@ static int load_flat_binary(struct linux_binprm *bprm) > #endif > stack_len += (bprm->argc + 1) * sizeof(char *); /* the argv array */ > stack_len += (bprm->envc + 1) * sizeof(char *); /* the envp array */ > - stack_len = ALIGN(stack_len, FLAT_STACK_ALIGN); > + stack_len = ALIGN(stack_len, flat_stack_align()); > > res = load_flat_file(bprm, &libinfo, 0, &stack_len); > if (res < 0) > diff --git a/include/crypto/hash.h b/include/crypto/hash.h > index f140e4643949..442c290f458c 100644 > --- a/include/crypto/hash.h > +++ b/include/crypto/hash.h > @@ -149,7 +149,7 @@ struct ahash_alg { > > struct shash_desc { > struct crypto_shash *tfm; > - void *__ctx[] __aligned(ARCH_SLAB_MINALIGN); > + void *__ctx[] __aligned(ARCH_SLAB_MIN_MINALIGN); > }; > > #define HASH_MAX_DIGESTSIZE 64 > diff --git a/include/linux/slab.h b/include/linux/slab.h > index 373b3ef99f4e..80e517593372 100644 > --- a/include/linux/slab.h > +++ b/include/linux/slab.h > @@ -201,21 +201,33 @@ void kmem_dump_obj(void *object); > #endif > > /* > - * Setting ARCH_SLAB_MINALIGN in arch headers allows a different alignment. > + * Setting ARCH_SLAB_MIN_MINALIGN in arch headers allows a different alignment. > * Intended for arches that get misalignment faults even for 64 bit integer > * aligned buffers. > */ > -#ifndef ARCH_SLAB_MINALIGN > -#define ARCH_SLAB_MINALIGN __alignof__(unsigned long long) > +#ifndef ARCH_SLAB_MIN_MINALIGN > +#define ARCH_SLAB_MIN_MINALIGN __alignof__(unsigned long long) > +#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 > + * >= ARCH_SLAB_MIN_MINALIGN. > + */ Not only the value should be bigger than or equal to ARCH_SLAB_MIN_MINALIGN, it should be compatible with ARCH_SLAB_MIN_MINALIGN. > +#ifndef arch_slab_minalign > +static inline size_t arch_slab_minalign(void) > +{ > + return ARCH_SLAB_MIN_MINALIGN; > +} > #endif > > /* > * kmalloc and friends return ARCH_KMALLOC_MINALIGN aligned > - * pointers. kmem_cache_alloc and friends return ARCH_SLAB_MINALIGN > + * pointers. kmem_cache_alloc and friends return ARCH_SLAB_MIN_MINALIGN > * aligned pointers. > */ > #define __assume_kmalloc_alignment __assume_aligned(ARCH_KMALLOC_MINALIGN) > -#define __assume_slab_alignment __assume_aligned(ARCH_SLAB_MINALIGN) > +#define __assume_slab_alignment __assume_aligned(ARCH_SLAB_MIN_MINALIGN) > #define __assume_page_alignment __assume_aligned(PAGE_SIZE) > > /* > diff --git a/mm/slab.c b/mm/slab.c > index 0edb474edef1..97b756976c8b 100644 > --- a/mm/slab.c > +++ b/mm/slab.c > @@ -3009,10 +3009,9 @@ static void *cache_alloc_debugcheck_after(struct kmem_cache *cachep, > 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; > } > diff --git a/mm/slab_common.c b/mm/slab_common.c > index 2b3206a2c3b5..33cc49810a54 100644 > --- a/mm/slab_common.c > +++ b/mm/slab_common.c > @@ -154,8 +154,7 @@ static unsigned int calculate_alignment(slab_flags_t flags, > 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 *)); > } > diff --git a/mm/slob.c b/mm/slob.c > index 40ea6e2d4ccd..3bd2669bd690 100644 > --- a/mm/slob.c > +++ b/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; > } > -- > 2.36.0.rc0.470.gd361397f0d-goog > > -- Thanks, Hyeonggon
