Frontswap: config and doc files

@@ -19,6 +19,7 @@ obj-$(CONFIG_HAVE_MEMBLOCK) += memblock.
 
 obj-$(CONFIG_BOUNCE)	+= bounce.o
 obj-$(CONFIG_SWAP)	+= page_io.o swap_state.o swapfile.o thrash.o
+obj-$(CONFIG_FRONTSWAP)	+= frontswap.o
 obj-$(CONFIG_HAS_DMA)	+= dmapool.o
 obj-$(CONFIG_HUGETLBFS)	+= hugetlb.o
 obj-$(CONFIG_NUMA) 	+= mempolicy.o

@@ -301,3 +301,20 @@ config NOMMU_INITIAL_TRIM_EXCESS
 	  of 1 says that all excess pages should be trimmed.
 
 	  See Documentation/nommu-mmap.txt for more information.
+
+config FRONTSWAP
+	bool "Enable frontswap pseudo-RAM driver to cache swap pages"
+	default y
+	help
+ 	  Frontswap is so named because it can be thought of as the opposite of
+ 	  a "backing" store for a swap device.  The storage is assumed to be
+ 	  a synchronous concurrency-safe page-oriented pseudo-RAM device (such
+	  as Xen's Transcendent Memory, aka "tmem") which is not directly
+	  accessible or addressable by the kernel and is of unknown (and
+	  possibly time-varying) size.  When a pseudo-RAM device is available,
+	  a signficant swap I/O reduction may be achieved.  When none is
+	  available, all frontswap calls are reduced to a single pointer-
+	  compare-against-NULL resulting in a negligible performance hit.
+
+	  If unsure, say Y to enable frontswap.
+

@@ -0,0 +1,16 @@
+What:		/sys/kernel/mm/frontswap/
+Date:		June 2010
+Contact:	Dan Magenheimer <[email protected]>
+Description:
+		/sys/kernel/mm/frontswap/ contains a number of files which
+		record a count of various frontswap operations (sum across
+		all swap devices):
+			succ_puts
+			failed_puts
+			gets
+			flushes
+		In addition, reading the curr_pages file shows how many
+		pages are currently contained in frontswap and writing this
+		file with an integer performs a "partial swapoff", reducing
+		the number of frontswap pages to that integer if memory
+		constraints permit.

209 lines not on this page · raw message