[PATCH v2] zsmalloc: Add Kconfig for enabling PTE method

[Minchan Kim <minchan@kernel.org>]

Zsmalloc has two methods 1) copy-based and 2) pte-based to access
allocations that span two pages. You can see history why we supported
two approach from [1].

In summary, copy-based method is 3 times fater in x86 while pte-based
is 6 times faster in ARM.

But it was bad choice that adding hard coding to select architecture
which want to use pte based method. This patch removed it and adds
new Kconfig to select the approach.

This patch is based on next-20130205.

[1] https://lkml.org/lkml/2012/7/11/58

* Changelog from v1
  * Fix CONFIG_PGTABLE_MAPPING in zsmalloc-main.c - Greg

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Seth Jennings <sjenning@linux.vnet.ibm.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Dan Magenheimer <dan.magenheimer@oracle.com>
Cc: Konrad Rzeszutek Wilk <konrad@darnok.org>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 drivers/staging/zsmalloc/Kconfig         | 12 ++++++++++++
 drivers/staging/zsmalloc/zsmalloc-main.c | 20 +++++---------------
 2 files changed, 17 insertions(+), 15 deletions(-)

diff --git a/drivers/staging/zsmalloc/Kconfig b/drivers/staging/zsmalloc/Kconfig
index 9084565..232b3b6 100644
--- a/drivers/staging/zsmalloc/Kconfig
+++ b/drivers/staging/zsmalloc/Kconfig
@@ -8,3 +8,15 @@ config ZSMALLOC
 	  non-standard allocator interface where a handle, not a pointer, is
 	  returned by an alloc().  This handle must be mapped in order to
 	  access the allocated space.
+
+config PGTABLE_MAPPING
+        bool "Use page table mapping to access allocations that span two pages"
+        depends on ZSMALLOC
+        default n
+        help
+	  By default, zsmalloc uses a copy-based object mapping method to access
+	  allocations that span two pages. However, if a particular architecture
+	  performs VM mapping faster than copying, then you should select this.
+	  This causes zsmalloc to use page table mapping rather than copying
+	  for object mapping. You can check speed with zsmalloc benchmark[1].
+	  [1] https://github.com/spartacus06/zsmalloc
diff --git a/drivers/staging/zsmalloc/zsmalloc-main.c b/drivers/staging/zsmalloc/zsmalloc-main.c
index 06f73a9..2c1805c 100644
--- a/drivers/staging/zsmalloc/zsmalloc-main.c
+++ b/drivers/staging/zsmalloc/zsmalloc-main.c
@@ -207,6 +207,7 @@ struct zs_pool {
 	struct size_class size_class[ZS_SIZE_CLASSES];
 
 	gfp_t flags;	/* allocation flags used when growing pool */
+
 };
 
 /*
@@ -218,19 +219,8 @@ struct zs_pool {
 #define CLASS_IDX_MASK	((1 << CLASS_IDX_BITS) - 1)
 #define FULLNESS_MASK	((1 << FULLNESS_BITS) - 1)
 
-/*
- * By default, zsmalloc uses a copy-based object mapping method to access
- * allocations that span two pages. However, if a particular architecture
- * performs VM mapping faster than copying, then it should be added here
- * so that USE_PGTABLE_MAPPING is defined. This causes zsmalloc to use
- * page table mapping rather than copying for object mapping.
-*/
-#if defined(CONFIG_ARM)
-#define USE_PGTABLE_MAPPING
-#endif
-
 struct mapping_area {
-#ifdef USE_PGTABLE_MAPPING
+#ifdef CONFIG_PGTABLE_MAPPING
 	struct vm_struct *vm; /* vm area for mapping object that span pages */
 #else
 	char *vm_buf; /* copy buffer for objects that span pages */
@@ -622,7 +612,7 @@ static struct page *find_get_zspage(struct size_class *class)
 	return page;
 }
 
-#ifdef USE_PGTABLE_MAPPING
+#ifdef CONFIG_PGTABLE_MAPPING
 static inline int __zs_cpu_up(struct mapping_area *area)
 {
 	/*
@@ -663,7 +653,7 @@ static inline void __zs_unmap_object(struct mapping_area *area,
 	flush_tlb_kernel_range(addr, end);
 }
 
-#else /* USE_PGTABLE_MAPPING */
+#else /* CONFIG_PGTABLE_MAPPING*/
 
 static inline int __zs_cpu_up(struct mapping_area *area)
 {
@@ -741,7 +731,7 @@ out:
 	pagefault_enable();
 }
 
-#endif /* USE_PGTABLE_MAPPING */
+#endif /* CONFIG_PGTABLE_MAPPING */
 
 static int zs_cpu_notifier(struct notifier_block *nb, unsigned long action,
 				void *pcpu)
-- 
1.8.1.1

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