| Message ID | 20230518173403.1150549-1-catalin.marinas@arm.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | mm, dma, arm64: Reduce ARCH_KMALLOC_MINALIGN to 8 | expand |
On Thu, May 18, 2023 at 10:34 AM Catalin Marinas <catalin.marinas@arm.com> wrote: > > That's the fourth version of the series reducing the kmalloc() minimum > alignment on arm64 to 8 (from 128). Lovely. On my M2 Macbook air, I right now have about 24MB in the kmalloc-128 bucket, and most of it is presumably just 16 byte allocations (judging by my x86-64 slabinfo). I guess it doesn't really matter when I have 16GB in the machine, but this has annoyed me for a while. It feels like this is ready for 6.5, no? Linus
On Thu, 18 May 2023 at 19:56, Linus Torvalds <torvalds@linux-foundation.org> wrote: > > On Thu, May 18, 2023 at 10:34 AM Catalin Marinas > <catalin.marinas@arm.com> wrote: > > > > That's the fourth version of the series reducing the kmalloc() minimum > > alignment on arm64 to 8 (from 128). For the series: Tested-by: Ard Biesheuvel <ardb@kernel.org> # tx2 and I am seeing lots of smaller allocations, all of which would have otherwise taken up 128 or 256 bytes: kmalloc-192 6426 6426 192 42 2 : tunables 0 0 0 : slabdata 153 153 0 kmalloc-128 9472 9472 128 64 2 : tunables 0 0 0 : slabdata 148 148 0 kmalloc-96 15666 15666 96 42 1 : tunables 0 0 0 : slabdata 373 373 0 kmalloc-64 21952 21952 64 64 1 : tunables 0 0 0 : slabdata 343 343 0 kmalloc-32 23424 23424 32 128 1 : tunables 0 0 0 : slabdata 183 183 0 kmalloc-16 41216 41216 16 256 1 : tunables 0 0 0 : slabdata 161 161 0 kmalloc-8 77846 80384 8 512 1 : tunables 0 0 0 : slabdata 157 157 0 The box is fully DMA coherent, of course, so this doesn't really tell us whether the swiotlb DMA bouncing stuff works or not. > > Lovely. On my M2 Macbook air, I right now have about 24MB in the > kmalloc-128 bucket, and most of it is presumably just 16 byte > allocations (judging by my x86-64 slabinfo). > > I guess it doesn't really matter when I have 16GB in the machine, but > this has annoyed me for a while. > Yeah but surely the overhead in terms of D-cache footprint is a factor here too? > It feels like this is ready for 6.5, no? > Yes, please...
On Thu, May 18, 2023 at 10:56:24AM -0700, Linus Torvalds wrote: > On Thu, May 18, 2023 at 10:34 AM Catalin Marinas > <catalin.marinas@arm.com> wrote: > > > > That's the fourth version of the series reducing the kmalloc() minimum > > alignment on arm64 to 8 (from 128). > > Lovely. On my M2 Macbook air, I right now have about 24MB in the > kmalloc-128 bucket, and most of it is presumably just 16 byte > allocations (judging by my x86-64 slabinfo). > > I guess it doesn't really matter when I have 16GB in the machine, but > this has annoyed me for a while. > > It feels like this is ready for 6.5, no? From an implementation approach perspective, I definitely target 6.5. But I need help with testing this, especially the iommu bits (can buy Robin some beers ;)).
On Thu, May 18, 2023 at 08:13:08PM +0200, Ard Biesheuvel wrote: > On Thu, 18 May 2023 at 19:56, Linus Torvalds > <torvalds@linux-foundation.org> wrote: > > > > On Thu, May 18, 2023 at 10:34 AM Catalin Marinas > > <catalin.marinas@arm.com> wrote: > > > > > > That's the fourth version of the series reducing the kmalloc() minimum > > > alignment on arm64 to 8 (from 128). > > For the series: > > Tested-by: Ard Biesheuvel <ardb@kernel.org> # tx2 [...] > The box is fully DMA coherent, of course, so this doesn't really tell > us whether the swiotlb DMA bouncing stuff works or not. Thanks. On TX2, I forced the bouncing with: diff --git a/include/linux/dma-map-ops.h b/include/linux/dma-map-ops.h index 43bf50c35e14..9006bf680db0 100644 --- a/include/linux/dma-map-ops.h +++ b/include/linux/dma-map-ops.h @@ -296,7 +296,7 @@ static inline bool dma_kmalloc_safe(struct device *dev, * is coherent or the direction is DMA_TO_DEVICE (non-desctructive * cache maintenance and benign cache line evictions). */ - if (dev_is_dma_coherent(dev) || dir == DMA_TO_DEVICE) + if (/*dev_is_dma_coherent(dev) || */dir == DMA_TO_DEVICE) return true; return false;
Hi, That's the fourth version of the series reducing the kmalloc() minimum alignment on arm64 to 8 (from 128). The first 10 patches decouple ARCH_KMALLOC_MINALIGN from ARCH_DMA_MINALIGN and, for arm64, it limits the kmalloc() caches to those aligned to the run-time probed cache_line_size(). The advantage on arm64 is that we gain the kmalloc-{64,192} caches. The subsequent patches (11 to 15) further reduce the kmalloc() caches to kmalloc-{8,16,32,96} if the default swiotlb is present by bouncing small buffers in the DMA API. For iommu, following discussions with Robin, we concluded that it's still simpler to walk the sg list if the device is non-coherent and follow the bouncing path when any of the elements may originate from a small kmalloc() allocation. Main changes since v3: - Reorganise the series so that the first 10 patches could be applied before the DMA bouncing. They are still useful on arm64 reducing the kmalloc() alignment to 64. - There is no dma_sg_kmalloc_needs_bounce() function, it has been unrolled in the iommu_dma_sync_sg_for_device() function. - No crypto changes needed following Herbert's reworking of the crypto code (thanks!). The patches are also available on this branch: git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux devel/kmalloc-minalign Thanks. Catalin Marinas (14): mm/slab: Decouple ARCH_KMALLOC_MINALIGN from ARCH_DMA_MINALIGN dma: Allow dma_get_cache_alignment() to return the smaller cache_line_size() mm/slab: Simplify create_kmalloc_cache() args and make it static mm/slab: Limit kmalloc() minimum alignment to dma_get_cache_alignment() drivers/base: Use ARCH_DMA_MINALIGN instead of ARCH_KMALLOC_MINALIGN drivers/gpu: Use ARCH_DMA_MINALIGN instead of ARCH_KMALLOC_MINALIGN drivers/usb: Use ARCH_DMA_MINALIGN instead of ARCH_KMALLOC_MINALIGN drivers/spi: Use ARCH_DMA_MINALIGN instead of ARCH_KMALLOC_MINALIGN drivers/md: Use ARCH_DMA_MINALIGN instead of ARCH_KMALLOC_MINALIGN arm64: Allow kmalloc() caches aligned to the smaller cache_line_size() dma-mapping: Force bouncing if the kmalloc() size is not cache-line-aligned iommu/dma: Force bouncing if the size is not cacheline-aligned mm: slab: Reduce the kmalloc() minimum alignment if DMA bouncing possible arm64: Enable ARCH_WANT_KMALLOC_DMA_BOUNCE for arm64 Robin Murphy (1): scatterlist: Add dedicated config for DMA flags arch/arm64/Kconfig | 2 ++ arch/arm64/include/asm/cache.h | 1 + arch/arm64/mm/init.c | 7 ++++- drivers/base/devres.c | 6 ++--- drivers/gpu/drm/drm_managed.c | 6 ++--- drivers/iommu/dma-iommu.c | 25 ++++++++++++++---- drivers/md/dm-crypt.c | 2 +- drivers/pci/Kconfig | 1 + drivers/spi/spidev.c | 2 +- drivers/usb/core/buffer.c | 8 +++--- include/linux/dma-map-ops.h | 48 ++++++++++++++++++++++++++++++++++ include/linux/dma-mapping.h | 4 ++- include/linux/scatterlist.h | 29 +++++++++++++++++--- include/linux/slab.h | 16 +++++++++--- kernel/dma/Kconfig | 19 ++++++++++++++ kernel/dma/direct.h | 3 ++- mm/slab.c | 6 +---- mm/slab.h | 5 ++-- mm/slab_common.c | 43 +++++++++++++++++++++++------- 19 files changed, 188 insertions(+), 45 deletions(-)