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Subject[PATCH V2 4/4] Frontswap (was Transcendent Memory): config files
[PATCH V2 4/4] Frontswap (was Transcendent Memory): config files

Frontswap config defaults to on as the hooks devolve to
pointer-compare-to-NULL if no frontswap backend is provided.

Signed-off-by: Dan Magenheimer <dan.magenheimer@oracle.com>

Diffstat:
Kconfig | 16 ++++++++++++++++
Makefile | 1 +
2 files changed, 17 insertions(+)
--- linux-2.6.34/mm/Makefile 2010-05-16 15:17:36.000000000 -0600
+++ linux-2.6.34-frontswap/mm/Makefile 2010-05-21 12:59:10.000000000 -0600
@@ -17,6 +17,7 @@ obj-y += init-mm.o

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
--- linux-2.6.34/mm/Kconfig 2010-05-16 15:17:36.000000000 -0600
+++ linux-2.6.34-frontswap/mm/Kconfig 2010-05-21 12:59:10.000000000 -0600
@@ -287,3 +287,19 @@ 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.

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