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Wed, 05 Dec 2018 01:18:46 -0800 (PST) Date: Wed, 5 Dec 2018 09:18:45 +0000 From: Wei Yang To: Nicolas Boichat Cc: richard.weiyang@gmail.com, Will Deacon , Michal Hocko , Levin Alexander , linux-mm@kvack.org, Christoph Lameter , Huaisheng Ye , Matthew Wilcox , linux-arm Mailing List , David Rientjes , yingjoe.chen@mediatek.com, Vlastimil Babka , Tomasz Figa , Mike Rapoport , Matthias Brugger , Joonsoo Kim , Robin Murphy , lkml , Pekka Enberg , iommu@lists.linux-foundation.org, Andrew Morton , Mel Gorman Subject: Re: [PATCH v4 2/3] mm: Add support for kmem caches in DMA32 zone Message-ID: <20181205091845.kfro65nu7v4g6esa@master> Reply-To: Wei Yang References: <20181205054828.183476-1-drinkcat@chromium.org> <20181205054828.183476-3-drinkcat@chromium.org> <20181205072528.l7blg6y24ggblh4m@master> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Dec 05, 2018 at 03:39:51PM +0800, Nicolas Boichat wrote: >On Wed, Dec 5, 2018 at 3:25 PM Wei Yang wrote: >> >> On Wed, Dec 05, 2018 at 01:48:27PM +0800, Nicolas Boichat wrote: >> >In some cases (e.g. IOMMU ARMv7s page allocator), we need to allocate >> >data structures smaller than a page with GFP_DMA32 flag. >> > >> >This change makes it possible to create a custom cache in DMA32 zone >> >using kmem_cache_create, then allocate memory using kmem_cache_alloc. >> > >> >We do not create a DMA32 kmalloc cache array, as there are currently >> >no users of kmalloc(..., GFP_DMA32). The new test in check_slab_flags >> >ensures that such calls still fail (as they do before this change). >> > >> >Fixes: ad67f5a6545f ("arm64: replace ZONE_DMA with ZONE_DMA32") >> >Signed-off-by: Nicolas Boichat >> >--- >> > >> >Changes since v2: >> > - Clarified commit message >> > - Add entry in sysfs-kernel-slab to document the new sysfs file >> > >> >(v3 used the page_frag approach) >> > >> >Documentation/ABI/testing/sysfs-kernel-slab | 9 +++++++++ >> > include/linux/slab.h | 2 ++ >> > mm/internal.h | 8 ++++++-- >> > mm/slab.c | 4 +++- >> > mm/slab.h | 3 ++- >> > mm/slab_common.c | 2 +- >> > mm/slub.c | 18 +++++++++++++++++- >> > 7 files changed, 40 insertions(+), 6 deletions(-) >> > >> >diff --git a/Documentation/ABI/testing/sysfs-kernel-slab b/Documentation/ABI/testing/sysfs-kernel-slab >> >index 29601d93a1c2ea..d742c6cfdffbe9 100644 >> >--- a/Documentation/ABI/testing/sysfs-kernel-slab >> >+++ b/Documentation/ABI/testing/sysfs-kernel-slab >> >@@ -106,6 +106,15 @@ Description: >> > are from ZONE_DMA. >> > Available when CONFIG_ZONE_DMA is enabled. >> > >> >+What: /sys/kernel/slab/cache/cache_dma32 >> >+Date: December 2018 >> >+KernelVersion: 4.21 >> >+Contact: Nicolas Boichat >> >+Description: >> >+ The cache_dma32 file is read-only and specifies whether objects >> >+ are from ZONE_DMA32. >> >+ Available when CONFIG_ZONE_DMA32 is enabled. >> >+ >> > What: /sys/kernel/slab/cache/cpu_slabs >> > Date: May 2007 >> > KernelVersion: 2.6.22 >> >diff --git a/include/linux/slab.h b/include/linux/slab.h >> >index 11b45f7ae4057c..9449b19c5f107a 100644 >> >--- a/include/linux/slab.h >> >+++ b/include/linux/slab.h >> >@@ -32,6 +32,8 @@ >> > #define SLAB_HWCACHE_ALIGN ((slab_flags_t __force)0x00002000U) >> > /* Use GFP_DMA memory */ >> > #define SLAB_CACHE_DMA ((slab_flags_t __force)0x00004000U) >> >+/* Use GFP_DMA32 memory */ >> >+#define SLAB_CACHE_DMA32 ((slab_flags_t __force)0x00008000U) >> > /* DEBUG: Store the last owner for bug hunting */ >> > #define SLAB_STORE_USER ((slab_flags_t __force)0x00010000U) >> > /* Panic if kmem_cache_create() fails */ >> >diff --git a/mm/internal.h b/mm/internal.h >> >index a2ee82a0cd44ae..fd244ad716eaf8 100644 >> >--- a/mm/internal.h >> >+++ b/mm/internal.h >> >@@ -14,6 +14,7 @@ >> > #include >> > #include >> > #include >> >+#include >> > #include >> > >> > /* >> >@@ -34,9 +35,12 @@ >> > #define GFP_CONSTRAINT_MASK (__GFP_HARDWALL|__GFP_THISNODE) >> > >> > /* Check for flags that must not be used with a slab allocator */ >> >-static inline gfp_t check_slab_flags(gfp_t flags) >> >+static inline gfp_t check_slab_flags(gfp_t flags, slab_flags_t slab_flags) >> > { >> >- gfp_t bug_mask = __GFP_DMA32 | __GFP_HIGHMEM | ~__GFP_BITS_MASK; >> >+ gfp_t bug_mask = __GFP_HIGHMEM | ~__GFP_BITS_MASK; >> >+ >> >+ if (!IS_ENABLED(CONFIG_ZONE_DMA32) || !(slab_flags & SLAB_CACHE_DMA32)) >> >+ bug_mask |= __GFP_DMA32; >> >> The original version doesn't check CONFIG_ZONE_DMA32. >> >> Do we need to add this condition here? >> Could we just decide the bug_mask based on slab_flags? > >We can. The reason I did it this way is that when we don't have >CONFIG_ZONE_DMA32, the compiler should be able to simplify to: > >bug_mask = __GFP_HIGHMEM | ~__GFP_BITS_MASK; >if (true || ..) => if (true) > bug_mask |= __GFP_DMA32; > >Then just >bug_mask = __GFP_HIGHMEM | ~__GFP_BITS_MASK | __GFP_DMA32; > >And since the function is inline, slab_flags would not even need to be >accessed at all. > Thanks for explanation. This make sense to me. -- Wei Yang Help you, Help me