zcache is the remaining piece of code required to support in-kernel memory compression. The other two features, cleancache and frontswap, have been promoted to mainline in 3.0 and 3.5 respectively. This patchset promotes zcache from the staging tree to mainline.
Based on the level of activity and contributions we're seeing from a diverse set of people and interests, I think zcache has matured to the point where it makes sense to promote this out of staging. Overview ======== zcache is a backend to frontswap and cleancache that accepts pages from those mechanisms and compresses them, leading to reduced I/O caused by swap and file re-reads. This is very valuable in shared storage situations to reduce load on things like SANs. Also, in the case of slow backing/swap devices, zcache can also yield a performance gain. In-Kernel Memory Compression Overview: swap subsystem page cache + + frontswap cleancache + + zcache frontswap glue zcache cleancache glue + + +---------+------------+ + zcache/tmem core + +---------+------------+ + + zsmalloc zbud Everything below the frontswap/cleancache layer is current inside the zcache driver expect for zsmalloc which is a shared between zcache and another memory compression driver, zram. Since zcache is dependent on zsmalloc, it is also being promoted by this patchset. For information on zsmalloc and the rationale behind it's design and use cases verses already existing allocators in the kernel: https://lkml.org/lkml/2012/1/9/386 zsmalloc is the allocator used by zcache to store persistent pages that comes from frontswap, as opposed to zbud which is the (internal) allocator used for ephemeral pages from cleancache. zsmalloc uses many fields of the page struct to create it's conceptual high-order page called a zspage. Exactly which fields are used and for what purpose is documented at the top of the zsmalloc .c file. Because zsmalloc uses struct page extensively, Andrew advised that the promotion location be mm/: https://lkml.org/lkml/2012/1/20/308 Some benchmarking numbers demonstrating the I/O saving that can be had with zcache: https://lkml.org/lkml/2012/3/22/383 Dan's presentation at LSF/MM this year on zcache: http://oss.oracle.com/projects/tmem/dist/documentation/presentations/LSFMM12-zcache-final.pdf There was a recent thread about cleancache memory corruption that is resolved by this patch that should be making it into linux-next via Greg very soon: https://lkml.org/lkml/2012/8/29/253 Changlog: v2: * rebased to next-20120904 * removed already accepted patch from patchset Seth Jennings (3): zsmalloc: promote to mm/ drivers: add memory management driver class zcache: promote to drivers/mm/ drivers/Kconfig | 2 ++ drivers/Makefile | 1 + drivers/mm/Kconfig | 13 +++++++++++++ drivers/mm/Makefile | 1 + drivers/{staging => mm}/zcache/Makefile | 0 drivers/{staging => mm}/zcache/tmem.c | 0 drivers/{staging => mm}/zcache/tmem.h | 0 drivers/{staging => mm}/zcache/zcache-main.c | 4 ++-- drivers/staging/Kconfig | 4 ---- drivers/staging/Makefile | 2 -- drivers/staging/zcache/Kconfig | 11 ----------- drivers/staging/zram/zram_drv.h | 3 +-- drivers/staging/zsmalloc/Kconfig | 10 ---------- drivers/staging/zsmalloc/Makefile | 3 --- .../staging/zsmalloc => include/linux}/zsmalloc.h | 0 mm/Kconfig | 18 ++++++++++++++++++ mm/Makefile | 1 + .../zsmalloc/zsmalloc-main.c => mm/zsmalloc.c | 3 +-- 18 files changed, 40 insertions(+), 36 deletions(-) create mode 100644 drivers/mm/Kconfig create mode 100644 drivers/mm/Makefile rename drivers/{staging => mm}/zcache/Makefile (100%) rename drivers/{staging => mm}/zcache/tmem.c (100%) rename drivers/{staging => mm}/zcache/tmem.h (100%) rename drivers/{staging => mm}/zcache/zcache-main.c (99%) delete mode 100644 drivers/staging/zcache/Kconfig delete mode 100644 drivers/staging/zsmalloc/Kconfig delete mode 100644 drivers/staging/zsmalloc/Makefile rename {drivers/staging/zsmalloc => include/linux}/zsmalloc.h (100%) rename drivers/staging/zsmalloc/zsmalloc-main.c => mm/zsmalloc.c (99%) -- 1.7.9.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/