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Wed, 05 Dec 2018 19:32:57 -0800 (PST) Date: Thu, 6 Dec 2018 03:32:57 +0000 From: Wei Yang To: Nicolas Boichat Subject: Re: [PATCH v4 2/3] mm: Add support for kmem caches in DMA32 zone Message-ID: <20181206033257.mmgh6efejee2i2ae@master> References: <20181205054828.183476-1-drinkcat@chromium.org> <20181205054828.183476-3-drinkcat@chromium.org> <20181205072528.l7blg6y24ggblh4m@master> <20181205121807.evmslrimsv4pdtza@master> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170113 (1.7.2) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20181205_193310_518123_E85BB98D X-CRM114-Status: GOOD ( 24.33 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Wei Yang Cc: Michal Hocko , Will Deacon , richard.weiyang@gmail.com, Levin Alexander , linux-mm@kvack.org, Christoph Lameter , Huaisheng Ye , Matthew Wilcox , linux-arm Mailing List , David Rientjes , yingjoe.chen@mediatek.com, Tomasz Figa , Mike Rapoport , Matthias Brugger , Joonsoo Kim , Vlastimil Babka , Robin Murphy , lkml , Pekka Enberg , iommu@lists.linux-foundation.org, Andrew Morton , Mel Gorman Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Dec 06, 2018 at 08:41:36AM +0800, Nicolas Boichat wrote: >On Wed, Dec 5, 2018 at 8:18 PM Wei Yang wrote: >> >> 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. >> > >> >> Hmm, I get one confusion. >> >> This means if CONFIG_ZONE_DMA32 is not enabled, bug_mask will always >> contains __GFP_DMA32. This will check with cachep->flags. >> >> If cachep->flags has GFP_DMA32, this always fail? >> >> Is this possible? > >Not fully sure to understand the question, but the code is: >if (!IS_ENABLED(CONFIG_ZONE_DMA32) || !(slab_flags & SLAB_CACHE_DMA32)) > bug_mask |= __GFP_DMA32; > >IS_ENABLED(CONFIG_ZONE_DMA32) == true: > - (slab_flags & SLAB_CACHE_DMA32) => bug_mask untouched, __GFP_DMA32 >is allowed. > - !(slab_flags & SLAB_CACHE_DMA32) => bug_mask |= __GFP_DMA32;, >__GFP_DMA32 triggers warning >IS_ENABLED(CONFIG_ZONE_DMA32) == false: > => bug_mask |= __GFP_DMA32;, __GFP_DMA32 triggers warning (as >expected, GFP_DMA32 does not make sense if there is no DMA32 zone). This is the case I am thinking. The warning is reasonable since there is no DMA32. While the kmem_cache_create() user is not easy to change their code. For example, one writes code and wants to have a kmem_cache with DMA32 capability, so he writes kmem_cache_create(__GFP_DMA32). The code is there and not easy to change. But one distro builder decides to disable DMA32. This will leads to all the kmem_cache_create() through warning? This behavior is what we expect? > >Does that clarify? > >> >> -- >> Wei Yang >> Help you, Help me -- Wei Yang Help you, Help me _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel