mm: cleancache core ops functions and config

This third patch of eight in this cleancache series provides
the core code for cleancache that interfaces between the hooks in
VFS and individual filesystems and a cleancache backend.  It also
includes build and config patches.

Two new files are added: mm/cleancache.c and include/linux/cleancache.h.

Note that CONFIG_CLEANCACHE can default to on; in systems that do
not provide a cleancache backend, all hooks devolve to a simple
check of a global enable flag, so performance impact should
be negligible but can be reduced to zero impact if config'ed off.
However for this first commit, it defaults to off.

Details and a FAQ can be found in Documentation/vm/cleancache.txt

Credits: Cleancache_ops design derived from Jeremy Fitzhardinge
design for tmem

[v8: dan.magenheimer@oracle.com: fix exportfs call affecting btrfs]
[v8: akpm@linux-foundation.org: use static inline function, not macro]
[v7: dan.magenheimer@oracle.com: cleanup sysfs and remove cleancache prefix]
[v6: JBeulich@novell.com: robustly handle buggy fs encode_fh actor definition]
[v5: jeremy@goop.org: clean up global usage and static var names]
[v5: jeremy@goop.org: simplify init hook and any future fs init changes]
[v5: hch@infradead.org: cleaner non-global interface for ops registration]
[v4: adilger@sun.com: interface must support exportfs FS's]
[v4: hch@infradead.org: interface must support 64-bit FS on 32-bit kernel]
[v3: akpm@linux-foundation.org: use one ops struct to avoid pointer hops]
[v3: akpm@linux-foundation.org: document and ensure PageLocked reqts are met]
[v3: ngupta@vflare.org: fix success/fail codes, change funcs to void]
[v2: viro@ZenIV.linux.org.uk: use sane types]
Signed-off-by: Dan Magenheimer <dan.magenheimer@oracle.com>
Reviewed-by: Jeremy Fitzhardinge <jeremy@goop.org>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Acked-by: Al Viro <viro@ZenIV.linux.org.uk>
Acked-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Nitin Gupta <ngupta@vflare.org>
Acked-by: Minchan Kim <minchan.kim@gmail.com>
Acked-by: Andreas Dilger <adilger@sun.com>
Acked-by: Jan Beulich <JBeulich@novell.com>
Cc: Matthew Wilcox <matthew@wil.cx>
Cc: Nick Piggin <npiggin@kernel.dk>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Rik Van Riel <riel@redhat.com>
Cc: Chris Mason <chris.mason@oracle.com>
Cc: Ted Ts'o <tytso@mit.edu>
Cc: Mark Fasheh <mfasheh@suse.com>
Cc: Joel Becker <joel.becker@oracle.com>

1 files changed, 23 insertions, 0 deletions

diff --git a/mm/Kconfig b/mm/Kconfig
index e9c0c61f2ddd..8ca47a5ee9c8 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -347,3 +347,26 @@ config NEED_PER_CPU_KM
         depends on !SMP
         bool
         default y
+
+config CLEANCACHE
+        bool "Enable cleancache driver to cache clean pages if tmem is present"
+        default n
+        help
+          Cleancache can be thought of as a page-granularity victim cache
+          for clean pages that the kernel's pageframe replacement algorithm
+          (PFRA) would like to keep around, but can't since there isn't enough
+          memory.  So when the PFRA "evicts" a page, it first attempts to use
+          cleancacne code to put the data contained in that page into
+          "transcendent memory", memory that is not directly accessible or
+          addressable by the kernel and is of unknown and possibly
+          time-varying size.  And when a cleancache-enabled
+          filesystem wishes to access a page in a file on disk, it first
+          checks cleancache to see if it already contains it; if it does,
+          the page is copied into the kernel and a disk access is avoided.
+          When a transcendent memory driver is available (such as zcache or
+          Xen transcendent memory), a significant I/O reduction
+          may be achieved.  When none is available, all cleancache calls
+          are reduced to a single pointer-compare-against-NULL resulting
+          in a negligible performance hit.
+
+          If unsure, say Y to enable cleancache