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* frontswap: support exclusive gets if tmem backend is capableDan Magenheimer2012-09-211-0/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Tmem, as originally specified, assumes that "get" operations performed on persistent pools never flush the page of data out of tmem on a successful get, waiting instead for a flush operation. This is intended to mimic the model of a swap disk, where a disk read is non-destructive. Unlike a disk, however, freeing up the RAM can be valuable. Over the years that frontswap was in the review process, several reviewers (and notably Hugh Dickins in 2010) pointed out that this would result, at least temporarily, in two copies of the data in RAM: one (compressed for zcache) copy in tmem, and one copy in the swap cache. We wondered if this could be done differently, at least optionally. This patch allows tmem backends to instruct the frontswap code that this backend performs exclusive gets. Zcache2 already contains hooks to support this feature. Other backends are completely unaffected unless/until they are updated to support this feature. While it is not clear that exclusive gets are a performance win on all workloads at all times, this small patch allows for experimentation by backends. P.S. Let's not quibble about the naming of "get" vs "read" vs "load" etc. The naming is currently horribly inconsistent between cleancache and frontswap and existing tmem backends, so will need to be straightened out as a separate patch. "Get" is used by the tmem architecture spec, existing backends, and all documentation and presentation material so I am using it in this patch. Signed-off-by: Dan Magenheimer <dan.magenheimer@oracle.com> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
* frontswap: s/put_page/store/g s/get_page/loadKonrad Rzeszutek Wilk2012-05-151-8/+8
| | | | | | | Sounds so much more natural. Suggested-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
* mm: frontswap: add frontswap header fileDan Magenheimer2012-05-151-0/+127
Frontswap is the alter ego of cleancache, the "yang" to cleancache's "yin"... and more precisely frontswap is the provider of anonymous pages to transcendent memory to nicely complement cleancache's providing of clean pagecache pages to transcendent memory. For optimal use of transcendent memory, both are necessary... because a kernel under memory pressure first reclaims clean pagecache pages and, when under more memory pressure, starts swapping anonymous pages. Frontswap and cleancache (which was merged at 3.0) are the "frontends" and the only necessary changes to the core kernel for transcendent memory; all other supporting code -- the "backends" -- is implemented as drivers. See the LWN.net article "Transcendent memory in a nutshell" for a detailed overview of frontswap and related kernel parts: https://lwn.net/Articles/454795/ Frontswap code was first posted publicly in January 2009 and on LKML in May 2009, and has remained functionally stable for nearly three years now. It is barely invasive, touching only the swap subsystem and adds less than 100 lines of code to existing swap subsystem code files. It has improved syntactically substantially between V1 and this posting of V14, thanks to the review of a few kernel developers, and has adapted easily to at least one major swap subsystem change. As of 3.4, there are three in-tree users of frontswap patiently waiting for this patchset and for CONFIG_FRONTSWAP to be enabled: zcache (staging driver merged at 2.6.39), Xen tmem (merged at 3.0 and 3.1) and RAMster (staging driver merged at 3.4). In addition, a RFC has been posted for a KVM backend. The frontswap patchset has been in linux-next since next-110603. Earlier versions of frontswap already ship in the Oracle Unbreakable Enterprise Kernel and SuSE SLES. This patch, 1of4, provides the header file for the core code for frontswap that interfaces between the hooks in the swap subsystem and a frontswap backend via frontswap_ops. --- New file added: include/linux/frontswap.h [v14: add support for writethrough, per suggestion by aarcange@redhat.com] [v14: rebase to 3.4-rc2] [v11: konrad.wilk@oracle.com: squashed s/flush/invalidate/ in] [v10: no change] [v9: akpm@linux-foundation.org: change "flush" to "invalidate", part 1] [v8: rebase to 3.0-rc4] [v7: rebase to 3.0-rc3] [v7: JBeulich@novell.com: new static inlines resolve to no-ops if not config'd] [v7: JBeulich@novell.com: avoid redundant shifts/divides for *_bit lib calls] [v6: rebase to 3.1-rc1] [v5: no change from v4] [v4: rebase to 2.6.39] Signed-off-by: Dan Magenheimer <dan.magenheimer@oracle.com> Reviewed-by: Andrew Morton <akpm@linux-foundation.org> Acked-by: Jan Beulich <JBeulich@novell.com> Acked-by: Seth Jennings <sjenning@linux.vnet.ibm.com> Cc: Jeremy Fitzhardinge <jeremy@goop.org> Cc: Hugh Dickins <hughd@google.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Nitin Gupta <ngupta@vflare.org> Cc: Matthew Wilcox <matthew@wil.cx> Cc: Chris Mason <chris.mason@oracle.com> Cc: Rik Riel <riel@redhat.com> [v15: int/bool on some functions] Signed-off-by: Konrad Wilk <konrad.wilk@oracle.com>
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