zsmalloc: move it under mm

This patch moves zsmalloc under mm directory. Before that, description will explain why we have needed custom allocator. Zsmalloc is a new slab-based memory allocator for storing compressed pages. It is designed for low fragmentation and high allocation success rate on large object, but <= PAGE_SIZE allocations. zsmalloc differs from the kernel slab allocator in two primary ways to achieve these design goals. zsmalloc never requires high order page allocations to back slabs, or "size classes" in zsmalloc terms. Instead it allows multiple single-order pages to be stitched together into a "zspage" which backs the slab. This allows for higher allocation success rate under memory pressure. Also, zsmalloc allows objects to span page boundaries within the zspage. This allows for lower fragmentation than could be had with the kernel slab allocator for objects between PAGE_SIZE/2 and PAGE_SIZE. With the kernel slab allocator, if a page compresses to 60% of it original size, the memory savings gained through compression is lost in fragmentation because another object of the same size can't be stored in the leftover space. This ability to span pages results in zsmalloc allocations not being directly addressable by the user. The user is given an non-dereferencable handle in response to an allocation request. That handle must be mapped, using zs_map_object(), which returns a pointer to the mapped region that can be used. The mapping is necessary since the object data may reside in two different noncontigious pages. The zsmalloc fulfills the allocation needs for zram perfectly [[email protected]: borrow Seth's quote] Signed-off-by: Minchan Kim <[email protected]> Acked-by: Nitin Gupta <[email protected]> Reviewed-by: Konrad Rzeszutek Wilk <[email protected]> Cc: Bob Liu <[email protected]> Cc: Greg Kroah-Hartman <[email protected]> Cc: Hugh Dickins <[email protected]> Cc: Jens Axboe <[email protected]> Cc: Luigi Semenzato <[email protected]> Cc: Mel Gorman <[email protected]> Cc: Pekka Enberg <[email protected]> Cc: Rik van Riel <[email protected]> Cc: Seth Jennings <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
kyagi · Jan 31, 2014 · bcf1647 · bcf1647
1 parent 73f9455
commit bcf1647
Show file tree

Hide file tree

Showing 9 changed files with 28 additions and 34 deletions.
diff --git a/drivers/staging/Kconfig b/drivers/staging/Kconfig
@@ -76,8 +76,6 @@ source "drivers/staging/sep/Kconfig"
 
 source "drivers/staging/iio/Kconfig"
 
-source "drivers/staging/zsmalloc/Kconfig"
-
 source "drivers/staging/zram/Kconfig"
 
 source "drivers/staging/wlags49_h2/Kconfig"

diff --git a/drivers/staging/Makefile b/drivers/staging/Makefile
@@ -33,7 +33,6 @@ obj-$(CONFIG_VME_BUS)		+= vme/
 obj-$(CONFIG_DX_SEP)            += sep/
 obj-$(CONFIG_IIO)		+= iio/
 obj-$(CONFIG_ZRAM)		+= zram/
-obj-$(CONFIG_ZSMALLOC)		+= zsmalloc/
 obj-$(CONFIG_WLAGS49_H2)	+= wlags49_h2/
 obj-$(CONFIG_WLAGS49_H25)	+= wlags49_h25/
 obj-$(CONFIG_FB_SM7XX)		+= sm7xxfb/

diff --git a/drivers/staging/zram/zram_drv.h b/drivers/staging/zram/zram_drv.h
@@ -17,8 +17,7 @@
 
 #include <linux/spinlock.h>
 #include <linux/mutex.h>
-
-#include "../zsmalloc/zsmalloc.h"
+#include <linux/zsmalloc.h>
 
 /*
  * Some arbitrary value. This is just to catch

diff --git a/drivers/staging/zsmalloc/Kconfig b/drivers/staging/zsmalloc/Kconfig
diff --git a/drivers/staging/zsmalloc/Makefile b/drivers/staging/zsmalloc/Makefile
diff --git a/drivers/staging/zsmalloc/zsmalloc.h → include/linux/zsmalloc.h b/drivers/staging/zsmalloc/zsmalloc.h → include/linux/zsmalloc.h
diff --git a/mm/Kconfig b/mm/Kconfig
@@ -552,3 +552,28 @@ config MEM_SOFT_DIRTY
 	  it can be cleared by hands.
 
 	  See Documentation/vm/soft-dirty.txt for more details.
+
+config ZSMALLOC
+	bool "Memory allocator for compressed pages"
+	depends on MMU
+	default n
+	help
+	  zsmalloc is a slab-based memory allocator designed to store
+	  compressed RAM pages.  zsmalloc uses virtual memory mapping
+	  in order to reduce fragmentation.  However, this results in a
+	  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 object in zsmalloc"
+	depends on ZSMALLOC
+	help
+	  By default, zsmalloc uses a copy-based object mapping method to
+	  access allocations that span two pages. However, if a particular
+	  architecture (ex, ARM) 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/mm/Makefile b/mm/Makefile
@@ -60,3 +60,4 @@ obj-$(CONFIG_DEBUG_KMEMLEAK_TEST) += kmemleak-test.o
 obj-$(CONFIG_CLEANCACHE) += cleancache.o
 obj-$(CONFIG_MEMORY_ISOLATION) += page_isolation.o
 obj-$(CONFIG_ZBUD)	+= zbud.o
+obj-$(CONFIG_ZSMALLOC)	+= zsmalloc.o
diff --git a/drivers/staging/zsmalloc/zsmalloc-main.c → mm/zsmalloc.c b/drivers/staging/zsmalloc/zsmalloc-main.c → mm/zsmalloc.c
@@ -90,8 +90,7 @@
 #include <linux/hardirq.h>
 #include <linux/spinlock.h>
 #include <linux/types.h>
-
-#include "zsmalloc.h"
+#include <linux/zsmalloc.h>
 
 /*
  * This must be power of 2 and greater than of equal to sizeof(link_free).