On Mon, Nov 04, 2024 at 07:16:20PM +0100, Vlastimil Babka wrote:
On 11/4/24 19:00, Matthew Wilcox wrote:
On Tue, Nov 05, 2024 at 12:08:37AM +0900, Koichiro Den wrote:
Commit b035f5a6d852 ("mm: slab: reduce the kmalloc() minimum alignment if DMA bouncing possible") reduced ARCH_KMALLOC_MINALIGN to 8 on arm64. However, with KASAN_HW_TAGS enabled, arch_slab_minalign() becomes 16. This causes kmalloc_caches[*][8] to be aliased to kmalloc_caches[*][16], resulting in kmem_buckets_create() attempting to create a kmem_cache for size 16 twice. This duplication triggers warnings on boot:
Wouldn't this be easier?
They wanted it to depend on actual HW capability / kernel parameter, see d949a8155d13 ("mm: make minimum slab alignment a runtime property")
Also Catalin's commit referenced above was part of the series that made the alignment more dynamic for other cases IIRC. So I doubt we can simply reduce it back to a build-time constant.
I principle, I wouldn't reduce it back to constant though the 8 vs 16 difference is not significant. It matter if one enables KASAN_HW_TAGS and wants to run it on hardware without MTE, getting the *-8 caches back.
That said, I haven't managed to trigger this warning yet. Do I need other config options than KASAN_HW_TAGS and DEBUG_VM?