Re: [PATCH v4 2/3] mm: Add support for kmem caches in DMA32 zone

[Wei Yang]

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 <drinkcat@xxxxxxxxxxxx>
>---
>
>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 <drinkcat@xxxxxxxxxxxx>
>+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 <linux/fs.h>
> #include <linux/mm.h>
> #include <linux/pagemap.h>
>+#include <linux/slab.h>
> #include <linux/tracepoint-defs.h>
> 
> /*
>@@ -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?

> 
> 	if (unlikely(flags & bug_mask)) {
> 		gfp_t invalid_mask = flags & bug_mask;
>diff --git a/mm/slab.c b/mm/slab.c
>index 65a774f05e7836..2fd3b9a996cbe6 100644
>--- a/mm/slab.c
>+++ b/mm/slab.c
>@@ -2109,6 +2109,8 @@ int __kmem_cache_create(struct kmem_cache *cachep, slab_flags_t flags)
> 	cachep->allocflags = __GFP_COMP;
> 	if (flags & SLAB_CACHE_DMA)
> 		cachep->allocflags |= GFP_DMA;
>+	if (flags & SLAB_CACHE_DMA32)
>+		cachep->allocflags |= GFP_DMA32;
> 	if (flags & SLAB_RECLAIM_ACCOUNT)
> 		cachep->allocflags |= __GFP_RECLAIMABLE;
> 	cachep->size = size;
>@@ -2643,7 +2645,7 @@ static struct page *cache_grow_begin(struct kmem_cache *cachep,
> 	 * Be lazy and only check for valid flags here,  keeping it out of the
> 	 * critical path in kmem_cache_alloc().
> 	 */
>-	flags = check_slab_flags(flags);
>+	flags = check_slab_flags(flags, cachep->flags);
> 	WARN_ON_ONCE(cachep->ctor && (flags & __GFP_ZERO));
> 	local_flags = flags & (GFP_CONSTRAINT_MASK|GFP_RECLAIM_MASK);
> 
>diff --git a/mm/slab.h b/mm/slab.h
>index 4190c24ef0e9df..fcf717e12f0a86 100644
>--- a/mm/slab.h
>+++ b/mm/slab.h
>@@ -127,7 +127,8 @@ static inline slab_flags_t kmem_cache_flags(unsigned int object_size,
> 
> 
> /* Legal flag mask for kmem_cache_create(), for various configurations */
>-#define SLAB_CORE_FLAGS (SLAB_HWCACHE_ALIGN | SLAB_CACHE_DMA | SLAB_PANIC | \
>+#define SLAB_CORE_FLAGS (SLAB_HWCACHE_ALIGN | SLAB_CACHE_DMA | \
>+			 SLAB_CACHE_DMA32 | SLAB_PANIC | \
> 			 SLAB_TYPESAFE_BY_RCU | SLAB_DEBUG_OBJECTS )
> 
> #if defined(CONFIG_DEBUG_SLAB)
>diff --git a/mm/slab_common.c b/mm/slab_common.c
>index 70b0cc85db67f8..18b7b809c8d064 100644
>--- a/mm/slab_common.c
>+++ b/mm/slab_common.c
>@@ -53,7 +53,7 @@ static DECLARE_WORK(slab_caches_to_rcu_destroy_work,
> 		SLAB_FAILSLAB | SLAB_KASAN)
> 
> #define SLAB_MERGE_SAME (SLAB_RECLAIM_ACCOUNT | SLAB_CACHE_DMA | \
>-			 SLAB_ACCOUNT)
>+			 SLAB_CACHE_DMA32 | SLAB_ACCOUNT)
> 
> /*
>  * Merge control. If this is set then no merging of slab caches will occur.
>diff --git a/mm/slub.c b/mm/slub.c
>index 21a3f6866da472..6d47765a82d150 100644
>--- a/mm/slub.c
>+++ b/mm/slub.c
>@@ -1685,7 +1685,7 @@ static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node)
> 
> static struct page *new_slab(struct kmem_cache *s, gfp_t flags, int node)
> {
>-	flags = check_slab_flags(flags);
>+	flags = check_slab_flags(flags, s->flags);
> 
> 	return allocate_slab(s,
> 		flags & (GFP_RECLAIM_MASK | GFP_CONSTRAINT_MASK), node);
>@@ -3577,6 +3577,9 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
> 	if (s->flags & SLAB_CACHE_DMA)
> 		s->allocflags |= GFP_DMA;
> 
>+	if (s->flags & SLAB_CACHE_DMA32)
>+		s->allocflags |= GFP_DMA32;
>+
> 	if (s->flags & SLAB_RECLAIM_ACCOUNT)
> 		s->allocflags |= __GFP_RECLAIMABLE;
> 
>@@ -5095,6 +5098,14 @@ static ssize_t cache_dma_show(struct kmem_cache *s, char *buf)
> SLAB_ATTR_RO(cache_dma);
> #endif
> 
>+#ifdef CONFIG_ZONE_DMA32
>+static ssize_t cache_dma32_show(struct kmem_cache *s, char *buf)
>+{
>+	return sprintf(buf, "%d\n", !!(s->flags & SLAB_CACHE_DMA32));
>+}
>+SLAB_ATTR_RO(cache_dma32);
>+#endif
>+
> static ssize_t usersize_show(struct kmem_cache *s, char *buf)
> {
> 	return sprintf(buf, "%u\n", s->usersize);
>@@ -5435,6 +5446,9 @@ static struct attribute *slab_attrs[] = {
> #ifdef CONFIG_ZONE_DMA
> 	&cache_dma_attr.attr,
> #endif
>+#ifdef CONFIG_ZONE_DMA32
>+	&cache_dma32_attr.attr,
>+#endif
> #ifdef CONFIG_NUMA
> 	&remote_node_defrag_ratio_attr.attr,
> #endif
>@@ -5665,6 +5679,8 @@ static char *create_unique_id(struct kmem_cache *s)
> 	 */
> 	if (s->flags & SLAB_CACHE_DMA)
> 		*p++ = 'd';
>+	if (s->flags & SLAB_CACHE_DMA32)
>+		*p++ = 'D';
> 	if (s->flags & SLAB_RECLAIM_ACCOUNT)
> 		*p++ = 'a';
> 	if (s->flags & SLAB_CONSISTENCY_CHECKS)
>-- 
>2.20.0.rc1.387.gf8505762e3-goog
>
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-- 
Wei Yang
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