In some environments, dramatic performance savings may be obtained because
swapped pages are saved in RAM (or a RAM-like device) instead of a swap disk.
This tag provides the basic infrastructure along with some changes to the
existing backends.
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Merge tag 'stable/frontswap.v16-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/konrad/mm
Pull frontswap feature from Konrad Rzeszutek Wilk:
"Frontswap provides a "transcendent memory" interface for swap pages.
In some environments, dramatic performance savings may be obtained
because swapped pages are saved in RAM (or a RAM-like device) instead
of a swap disk. This tag provides the basic infrastructure along with
some changes to the existing backends."
Fix up trivial conflict in mm/Makefile due to removal of swap token code
changing a line next to the new frontswap entry.
This pull request came in before the merge window even opened, it got
delayed to after the merge window by me just wanting to make sure it had
actual users. Apparently IBM is using this on their embedded side, and
Jan Beulich says that it's already made available for SLES and OpenSUSE
users.
Also acked by Rik van Riel, and Konrad points to other people liking it
too. So in it goes.
By Dan Magenheimer (4) and Konrad Rzeszutek Wilk (2)
via Konrad Rzeszutek Wilk
* tag 'stable/frontswap.v16-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/konrad/mm:
frontswap: s/put_page/store/g s/get_page/load
MAINTAINER: Add myself for the frontswap API
mm: frontswap: config and doc files
mm: frontswap: core frontswap functionality
mm: frontswap: core swap subsystem hooks and headers
mm: frontswap: add frontswap header file
ZCACHE is a boolean in the Kconfig. When selected, it
should require that CRYPTO be builtin (=y).
Currently, ZCACHE=y and CRYPTO=m is a valid configuration
when it should not be.
This patch changes the zcache Kconfig to enforce this
dependency.
Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
into debugfs, and use __read_mostly as neccessary.
Also add a MAINTAINER file for cleancache API files.
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Merge tag 'stable/for-linus-3.4' of git://git.kernel.org/pub/scm/linux/kernel/git/konrad/mm
Pull cleancache changes from Konrad Rzeszutek Wilk:
"This has some patches for the cleancache API that should have been
submitted a _long_ time ago. They are basically cleanups:
- rename of flush to invalidate
- moving reporting of statistics into debugfs
- use __read_mostly as necessary.
Oh, and also the MAINTAINERS file change. The files (except the
MAINTAINERS file) have been in #linux-next for months now. The late
addition of MAINTAINERS file is a brain-fart on my side - didn't
realize I needed that just until I was typing this up - and I based
that patch on v3.3 - so the tree is on top of v3.3."
* tag 'stable/for-linus-3.4' of git://git.kernel.org/pub/scm/linux/kernel/git/konrad/mm:
MAINTAINERS: Adding cleancache API to the list.
mm: cleancache: Use __read_mostly as appropiate.
mm: cleancache: report statistics via debugfs instead of sysfs.
mm: zcache/tmem/cleancache: s/flush/invalidate/
mm: cleancache: s/flush/invalidate/
Pull kmap_atomic cleanup from Cong Wang.
It's been in -next for a long time, and it gets rid of the (no longer
used) second argument to k[un]map_atomic().
Fix up a few trivial conflicts in various drivers, and do an "evil
merge" to catch some new uses that have come in since Cong's tree.
* 'kmap_atomic' of git://github.com/congwang/linux: (59 commits)
feature-removal-schedule.txt: schedule the deprecated form of kmap_atomic() for removal
highmem: kill all __kmap_atomic() [swarren@nvidia.com: highmem: Fix ARM build break due to __kmap_atomic rename]
drbd: remove the second argument of k[un]map_atomic()
zcache: remove the second argument of k[un]map_atomic()
gma500: remove the second argument of k[un]map_atomic()
dm: remove the second argument of k[un]map_atomic()
tomoyo: remove the second argument of k[un]map_atomic()
sunrpc: remove the second argument of k[un]map_atomic()
rds: remove the second argument of k[un]map_atomic()
net: remove the second argument of k[un]map_atomic()
mm: remove the second argument of k[un]map_atomic()
lib: remove the second argument of k[un]map_atomic()
power: remove the second argument of k[un]map_atomic()
kdb: remove the second argument of k[un]map_atomic()
udf: remove the second argument of k[un]map_atomic()
ubifs: remove the second argument of k[un]map_atomic()
squashfs: remove the second argument of k[un]map_atomic()
reiserfs: remove the second argument of k[un]map_atomic()
ocfs2: remove the second argument of k[un]map_atomic()
ntfs: remove the second argument of k[un]map_atomic()
...
zcache cannot currently be loaded as a module. However
the Kconfig allows it to be built as a module; something that
the user probably does not intend since the module is not
loadable.
This patch switches zcache from a tristate to a bool in the Kconfig
Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Acked-by: Dan Magenheimer <dan.magenheimer@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This patch fixes a bug where the zv code writes before the allocated
buffer, resulting in system memory corruption. This was introduced
during the switch from xvmalloc to zsmalloc.
Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This fixes a type mismatch in the compression code where
a size_t pointer was cast to a unsigned int pointer. On
little endian archs, there is no issue. However on big
endian archs, the value is incorrect, taking the high
order bits and truncating the lower order bits.
Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Commit 9256a47 fixed a deadlock condition, being sure that the buddy
list spinlock is always taken before the page spinlock.
However in zbud_free_and_delist() locking order is the opposite
(page lock -> list lock).
Possible unsafe locking scenario (reported by lockdep):
CPU0 CPU1
---- ----
lock(&(&zbpg->lock)->rlock);
lock(zbud_budlists_spinlock);
lock(&(&zbpg->lock)->rlock);
lock(zbud_budlists_spinlock);
Fix by grabbing the locks in opposite order in zbud_free_and_delist().
Signed-off-by: Andrea Righi <andrea@betterlinux.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
linux/vmalloc.h added to zsmalloc-main.c to resolve implicit
declaration errors.
X86 dependency added to zsmalloc and dependent drivers zcache and zram.
This X86 only requirement is not ideal. Working to find portable
functions for __flush_tlb_one and set_pte.
Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This was done to resolve some merge issues with the following files that
had changed in both branches:
drivers/staging/rtl8712/rtl871x_sta_mgt.c
drivers/staging/tidspbridge/rmgr/drv_interface.c
drivers/staging/zcache/zcache-main.c
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Replaces xvmalloc with zsmalloc as the persistent memory allocator
for zcache
Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
In a multithreaded workload, the zv_curr_dist_counts
and zv_cumul_dist_counts statistics are being corrupted
because the increments and decrements in zv_create
and zv_free are not atomic.
This patch converts these statistics and their corresponding
increments/decrements/reads to atomic operations.
Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This patch allow zcache to use the crypto API for page compression.
It replaces the direct LZO compress/decompress calls with calls
into the crypto compression API. The compressor to be used is
specified in the kernel boot line with the zcache parameter like:
zcache=lzo or zcache=deflate. If the specified compressor can't
be loaded, zcache uses lzo as the default compressor.
Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Acked-by: Dan Magenheimer <dan.magenheimer@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
In a multithreaded workload, the zv_curr_dist_counts
and zv_cumul_dist_counts statistics are being corrupted
because the increments and decrements in zv_create
and zv_free are not atomic.
This patch converts these statistics and their corresponding
increments/decrements/reads to atomic operations.
Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Acked-by: Dan Magenheimer <dan.magenheimer@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
SWIZ_BITS > 8 results in a much larger number of "tmem_obj"
allocations, likely one per page-placed-in-frontswap. The
tmem_obj is not huge (roughly 100 bytes), but it is large
enough to add a not-insignificant memory overhead to zcache.
The SWIZ_BITS=8 will get roughly the same lock contention
without the space wastage.
The effect of SWIZ_BITS can be thought of as "2^SWIZ_BITS is
the number of unique oids that be generated" (This concept is
limited to frontswap's use of tmem).
Acked-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
I discovered this deadlock condition awhile ago working on RAMster
but it affects zcache as well. The list spinlock must be
locked prior to the page spinlock and released after. As
a result, the page copy must also be done while the locks are held.
Applies to 3.2. Konrad, please push (via GregKH?)...
this is definitely a bug fix so need not be pushed during
a -rc0 window.
Signed-off-by: Dan Magenheimer <dan.magenheimer@oracle.com>
Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Complete the renaming from "flush" to "invalidate" across
both tmem frontends (cleancache and frontswap) and both tmem backends
(Xen and zcache), as required by akpm.
This change is completely cosmetic.
[v10: no change]
[v9: akpm@linux-foundation.org: change "flush" to "invalidate", part 3]
Signed-off-by: Dan Magenheimer <dan.magenheimer@oracle.com>
Cc: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: 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>
Cc: Andrew Morton <akpm@linux-foundation.org>
[v11: Remove the frontswap part]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Function "strict_strtol" replaced by "kstrtol" as suggested by the checkpatch script
Signed-off-by: Bernhard Heinloth <bernhard@heinloth.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This was done to resolve a conflict in the
drivers/staging/comedi/drivers/ni_labpc.c file that resolved a build
bugfix in Linus's tree with a "better" bugfix that was in the
staging-next tree that resolved the issue in a more complete manner.
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
zcache_do_preload() currently does a spin_trylock() on the
zcache_direct_reclaim_lock. Holding this lock intends to prevent
shrink_zcache_memory() from evicting zbud pages as a result
of a preload.
However, it also prevents two threads from
executing zcache_do_preload() at the same time. The first
thread will obtain the lock and the second thread's spin_trylock()
will fail (an aborted preload) causing the page to be either lost
(cleancache) or pushed out to the swap device (frontswap). It
also doesn't ensure that the call to shrink_zcache_memory() is
on the same thread as the call to zcache_do_preload().
Additional, there is no need for this mechanism because all
zcache_do_preload() calls that come down from cleancache already
have PF_MEMALLOC set in the process flags which prevents
direct reclaim in the memory manager. If the zcache_do_preload()
call is done from the frontswap path, we _want_ reclaim to be
done (which it isn't right now).
This patch removes the zcache_direct_reclaim_lock and related
statistics in zcache.
Based on v3.1-rc8
Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Reviewed-by: Dave Hansen <dave@linux.vnet.ibm.com>
Acked-by: Dan Magenheimer <dan.magenheimer@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
tmem uses hash buckets each with their own rbtree and lock to
quickly lookup tmem objects. tmem has TMEM_HASH_BUCKETS (256)
buckets per pool. However, because of the way the tmem_oid is
generated for frontswap pages, only 16 unique tmem_oids are being
generated, resulting in only 16 of the 256 buckets being used.
This cause high lock contention for the per bucket locks.
This patch changes SWIZ_BITS to include more bits of the offset.
The result is that all 256 hash buckets are potentially used resulting in a
95% drop in hash bucket lock contention.
Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Acked-by: Dan Magenheimer <dan.magenheimer@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
In the case that a cpu is taken offline before zcache_do_preload() is
ever called on the cpu, the per-cpu zcache_preloads structure will
be uninitialized. In the CPU_DEAD case for zcache_cpu_notifier(),
kp->obj is not checked before calling kmem_cache_free() on it.
If it is NULL, a crash results.
This patch ensures that both kp->obj and kp->page are not NULL before
calling the respective free functions. In practice, just checking
one or the other should be sufficient since they are assigned together
in zcache_do_preload(), but I check both for safety.
Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Acked-by: Dave Hansen <dave@linux.vnet.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
After commit c5f5c4db39 ("staging: zcache: fix crash on high memory
swap") cleancache crashes on the first successful get. This was caused
by a remaining virt_to_page() call in zcache_pampd_get_data_and_free()
that only gets run in the cleancache path.
The patch converts the virt_to_page() to struct page casting like was
done for other instances in c5f5c4db39.
Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Tested-By: Valdis Kletnieks <valdis.kletnieks@vt.edu>
Acked-by: Dan Magenheimer <dan.magenheimer@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
"ret" needs to be signed for the error handling to work properly.
Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Dan Magenheimer <dan.magenheimer@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
zcache_put_page() was modified to pass page_address(page) instead of the
actual page structure. In combination with the function signature changes
to tmem_put() and zcache_pampd_create(), zcache_pampd_create() tries to
(re)derive the page structure from the virtual address. However, if the
original page is a high memory page (or any unmapped page), this
virt_to_page() fails because the page_address() in zcache_put_page()
returned NULL.
This patch changes zcache_put_page() and zcache_get_page() to pass
the page structure instead of the page's virtual address, which
may or may not exist.
Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Acked-by: Dan Magenheimer <dan.magenheimer@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
The patch fixes two typos in zcache-main.c
Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Acked-by: Dan Magenheimer <dan.magenheimer@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
zcache_new_pool() calls kmalloc() with GFP_KERNEL which has
__GFP_WAIT set. However, zcache_new_pool() gets called on
a stack that holds the swap_lock spinlock, leading to a
possible sleep-with-lock situation. The lock is obtained
in enable_swap_info().
The patch replaces GFP_KERNEL with GFP_ATOMIC.
v2: replace with GFP_ATOMIC, not GFP_IOFS
Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Acked-by: Dan Magenheimer <dan.magenheimer@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
xv_get_total_size_bytes returns a u64 value and it's used in a division.
This causes build failures in 32-bit architectures, as reported by Randy
Dunlap.
Reported-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@holoscopio.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Dan Magenheimer <dan.magenheimer@oracle.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Acked-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
The oncoming cleanup of module.h usage requires the explicit inclusion
of module.h when it was otherwise being included indirectly. Otherwise,
building zcache will fail.
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@holoscopio.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This avoids tainting the kernel as if a proprietary module was loaded.
The kernel will still be tainted because this is a staging driver.
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@holoscopio.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
zcache is only building tmem.c and not building zcache.c. To keep the
module name, zcache.c must be renamed if symbols from tmem.c are to
remain unexported.
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@holoscopio.com>
Acked-by: Dan Magenheimer <dan.magenheimer@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This is version 3 of an update to zcache, incorporating feedback from the list.
This patch adds support to the in-kernel transcendent memory ("tmem") code
and the zcache driver for multiple clients, which will be needed for both
RAMster and KVM support. It also adds additional tmem callbacks to support
RAMster and corresponding no-op stubs in the zcache driver. In v2, I've
also taken the liberty of adding some additional sysfs variables to
both surface information and allow policy control. Those experimenting
with zcache should find them useful. V3 clarifies some code walking
and declaring arrays.
Signed-off-by: Dan Magenheimer <dan.magenheimer@oracle.com>
[v3: error27@gmail.com: fix array bounds/walking]
[v2: konrad.wilk@oracle.com: fix bools, add check for NULL, fix a comment]
[v2: sjenning@linux.vnet.ibm.com: add info/tunables for poor compression]
[v2: marcusklemm@googlemail.com: add tunable for max persistent pages]
Acked-by: Dan Carpenter <error27@gmail.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: linux-mm@kvack.org
Cc: kvm@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Change each shrinker's API by consolidating the existing parameters into
shrink_control struct. This will simplify any further features added w/o
touching each file of shrinker.
[akpm@linux-foundation.org: fix build]
[akpm@linux-foundation.org: fix warning]
[kosaki.motohiro@jp.fujitsu.com: fix up new shrinker API]
[akpm@linux-foundation.org: fix xfs warning]
[akpm@linux-foundation.org: update gfs2]
Signed-off-by: Ying Han <yinghan@google.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Minchan Kim <minchan.kim@gmail.com>
Acked-by: Pavel Emelyanov <xemul@openvz.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Dave Hansen <dave@linux.vnet.ibm.com>
Cc: Steven Whitehouse <swhiteho@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Both zram and zcache use xvmalloc allocator. If xvmalloc
is compiled separately for both of them, we will get linker
error if they are both selected as "built-in". We can also
get linker error regarding missing xvmalloc symbols if zram
is not built.
So, we now compile xvmalloc separately and export its symbols
which are then used by both of zram and zcache.
Signed-off-by: Nitin Gupta <ngupta@vflare.org>
Acked-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
[PATCH V2 3/3] drivers/staging: zcache: misc build/config
Makefiles and Kconfigs to build zcache in drivers/staging
There is a dependency on xvmalloc.* which in 2.6.37 resides
in drivers/staging/zram. Should this move or disappear,
some Makefile/Kconfig changes will be required.
Signed-off-by: Dan Magenheimer <dan.magenheimer@oracle.com>
Signed-off-by: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
[PATCH V2 2/3] drivers/staging: zcache: host services and PAM services
Zcache provides host services (memory allocation) for tmem,
a "shim" to interface cleancache and frontswap to tmem, and
two different page-addressable memory implemenations using
lzo1x compression. The first, "compression buddies" ("zbud")
compresses pairs of pages and supplies a shrinker interface
that allows entire pages to be reclaimed. The second is
a shim to xvMalloc which is more space-efficient but
less receptive to page reclamation. The first is used
for ephemeral pools and the second for persistent pools.
All ephemeral pools share the same memory, that is, even
pages from different pools can share the same page.
Signed-off-by: Dan Magenheimer <dan.magenheimer@oracle.com>
Signed-off-by: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
[PATCH V2 1/3] drivers/staging: zcache: in-kernel tmem code
Transcendent memory ("tmem") is a clean API/ABI that provides
for an efficient address translation and a set of highly
concurrent access methods to copy data between a page-oriented
data source (e.g. cleancache or frontswap) and a page-addressable
memory ("PAM") data store. Of critical importance, the PAM data
store is of unknown (and possibly varying) size so any individual
access may succeed or fail as defined by the API/ABI.
Tmem exports a basic set of access methods (e.g. put, get,
flush, flush object, new pool, and destroy pool) which are
normally called from a "host" (e.g. zcache).
To be functional, two sets of "ops" must be registered by the
host, one to provide "host services" (memory allocation) and
one to provide page-addressable memory ("PAM") hooks.
Tmem supports one or more "clients", each which can provide
a set of "pools" to partition pages. Each pool contains
a set of "objects"; each object holds pointers to some number
of PAM page descriptors ("pampd"), indexed by an "index" number.
This triple <pool id, object id, index> is sometimes referred
to as a "handle". Tmem's primary function is to essentially
provide address translation of handles into pampds and move
data appropriately.
As an example, for cleancache, a pool maps to a filesystem,
an object maps to a file, and the index is the page offset
into the file. And in this patch, zcache is the host and
each PAM descriptor points to a compressed page of data.
Tmem supports two kinds of pages: "ephemeral" and "persistent".
Ephemeral pages may be asynchronously reclaimed "bottoms up"
so the data structures and concurrency model must allow for
this. For example, each pampd must retain sufficient information
to invalidate tmem's handle-to-pampd translation.
its containing object so that, on reclaim, all tmem data
structures can be made consistent.
Signed-off-by: Dan Magenheimer <dan.magenheimer@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Linus Torvalds