On Tue, Apr 05, 2022 at 02:57:49PM +0100, Catalin Marinas wrote: > In preparation for supporting a dynamic kmalloc() minimum alignment, > allow architectures to define ARCH_KMALLOC_MINALIGN independently of > ARCH_DMA_MINALIGN. In addition, always define ARCH_DMA_MINALIGN even if > an architecture does not override it. > [ +Cc slab maintainer/reviewers ] I get why you want to set minimum alignment of kmalloc() dynamically. That's because cache line size can be different and we cannot statically know that, right? But I don't get why you are trying to decouple ARCH_KMALLOC_MINALIGN from ARCH_DMA_MINALIGN. kmalloc'ed buffer is always supposed to be DMA-safe. I'm afraid this series may break some archs/drivers. in Documentation/dma-api-howto.rst: > 2) ARCH_DMA_MINALIGN > > Architectures must ensure that kmalloc'ed buffer is > DMA-safe. Drivers and subsystems depend on it. If an architecture > isn't fully DMA-coherent (i.e. hardware doesn't ensure that data in > the CPU cache is identical to data in main memory), > ARCH_DMA_MINALIGN must be set so that the memory allocator > makes sure that kmalloc'ed buffer doesn't share a cache line with > the others. See arch/arm/include/asm/cache.h as an example. > > Note that ARCH_DMA_MINALIGN is about DMA memory alignment > constraints. You don't need to worry about the architecture data > alignment constraints (e.g. the alignment constraints about 64-bit > objects). If I'm missing something, please let me know :) Thanks, Hyeonggon > After this patch, ARCH_DMA_MINALIGN is expected to be used in static > alignment annotations and defined by an architecture to be the maximum > alignment for all supported configurations/SoCs in a single Image. > ARCH_KMALLOC_MINALIGN, if different, is the minimum alignment guaranteed > by kmalloc(). > > Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > --- > include/linux/slab.h | 23 ++++++++++++++++++----- > 1 file changed, 18 insertions(+), 5 deletions(-) > > diff --git a/include/linux/slab.h b/include/linux/slab.h > index 373b3ef99f4e..d58211bdeceb 100644 > --- a/include/linux/slab.h > +++ b/include/linux/slab.h > @@ -187,17 +187,30 @@ bool kmem_valid_obj(void *object); > void kmem_dump_obj(void *object); > #endif > > +/* > + * slob does not support independent control of ARCH_KMALLOC_MINALIGN and > + * ARCH_DMA_MINALIGN. > + */ > +#ifdef CONFIG_SLOB > +#undef ARCH_KMALLOC_MINALIGN > +#endif > + > /* > * Some archs want to perform DMA into kmalloc caches and need a guaranteed > * alignment larger than the alignment of a 64-bit integer. > - * Setting ARCH_KMALLOC_MINALIGN in arch headers allows that. > + * Setting ARCH_DMA_MINALIGN in arch headers allows that. > */ > -#if defined(ARCH_DMA_MINALIGN) && ARCH_DMA_MINALIGN > 8 > +#ifndef ARCH_DMA_MINALIGN > +#define ARCH_DMA_MINALIGN __alignof__(unsigned long long) > +#elif ARCH_DMA_MINALIGN > 8 && !defined(ARCH_KMALLOC_MINALIGN) > #define ARCH_KMALLOC_MINALIGN ARCH_DMA_MINALIGN > -#define KMALLOC_MIN_SIZE ARCH_DMA_MINALIGN > -#define KMALLOC_SHIFT_LOW ilog2(ARCH_DMA_MINALIGN) > -#else > +#endif > + > +#ifndef ARCH_KMALLOC_MINALIGN > #define ARCH_KMALLOC_MINALIGN __alignof__(unsigned long long) > +#else > +#define KMALLOC_MIN_SIZE ARCH_KMALLOC_MINALIGN > +#define KMALLOC_SHIFT_LOW ilog2(KMALLOC_MIN_SIZE) > #endif > > /* >
