remove Xen tmem leftovers

remove Xen tmem leftovers

[Christoph Hellwig]

Hi all,

since the remove of the Xen tmem driver in 2019, the cleancache hooks are
entirely unused, as are large parts of frontswap.  This series against
linux-next (with the folio changes included) removes cleancaches, and cuts
down frontswap to the bits actually used by zswap.

Diffstat:
 Documentation/vm/cleancache.rst        |  296 -------------------------------
 b/Documentation/vm/frontswap.rst       |   31 ---
 b/Documentation/vm/index.rst           |    1 
 b/MAINTAINERS                          |    7 
 b/arch/arm/configs/bcm2835_defconfig   |    1 
 b/arch/arm/configs/qcom_defconfig      |    1 
 b/arch/m68k/configs/amiga_defconfig    |    1 
 b/arch/m68k/configs/apollo_defconfig   |    1 
 b/arch/m68k/configs/atari_defconfig    |    1 
 b/arch/m68k/configs/bvme6000_defconfig |    1 
 b/arch/m68k/configs/hp300_defconfig    |    1 
 b/arch/m68k/configs/mac_defconfig      |    1 
 b/arch/m68k/configs/multi_defconfig    |    1 
 b/arch/m68k/configs/mvme147_defconfig  |    1 
 b/arch/m68k/configs/mvme16x_defconfig  |    1 
 b/arch/m68k/configs/q40_defconfig      |    1 
 b/arch/m68k/configs/sun3_defconfig     |    1 
 b/arch/m68k/configs/sun3x_defconfig    |    1 
 b/arch/s390/configs/debug_defconfig    |    1 
 b/arch/s390/configs/defconfig          |    1 
 b/block/bdev.c                         |    5 
 b/fs/btrfs/extent_io.c                 |   10 -
 b/fs/btrfs/super.c                     |    2 
 b/fs/ext4/readpage.c                   |    6 
 b/fs/ext4/super.c                      |    3 
 b/fs/f2fs/data.c                       |    7 
 b/fs/mpage.c                           |    7 
 b/fs/ntfs3/ntfs_fs.h                   |    1 
 b/fs/ocfs2/super.c                     |    2 
 b/fs/super.c                           |    3 
 b/include/linux/frontswap.h            |   35 ---
 b/include/linux/fs.h                   |    5 
 b/include/linux/shmem_fs.h             |    3 
 b/include/linux/swapfile.h             |    3 
 b/mm/Kconfig                           |   40 ----
 b/mm/Makefile                          |    1 
 b/mm/filemap.c                         |   11 -
 b/mm/frontswap.c                       |  259 +--------------------------
 b/mm/shmem.c                           |   33 ---
 b/mm/swapfile.c                        |   90 ++-------
 b/mm/truncate.c                        |   15 -
 b/mm/zswap.c                           |    8 
 include/linux/cleancache.h             |  124 ------------
 mm/cleancache.c                        |  315 ---------------------------------
 44 files changed, 65 insertions(+), 1274 deletions(-)

[PATCH 01/13] mm: remove cleancache

[Christoph Hellwig]

The cleancache subsystem is unused since the removal of Xen tmem driver
in commit 814bbf49dcd0 ("xen: remove tmem driver").

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 Documentation/vm/cleancache.rst      | 296 -------------------------
 Documentation/vm/frontswap.rst       |  12 +-
 Documentation/vm/index.rst           |   1 -
 MAINTAINERS                          |   7 -
 arch/arm/configs/bcm2835_defconfig   |   1 -
 arch/arm/configs/qcom_defconfig      |   1 -
 arch/m68k/configs/amiga_defconfig    |   1 -
 arch/m68k/configs/apollo_defconfig   |   1 -
 arch/m68k/configs/atari_defconfig    |   1 -
 arch/m68k/configs/bvme6000_defconfig |   1 -
 arch/m68k/configs/hp300_defconfig    |   1 -
 arch/m68k/configs/mac_defconfig      |   1 -
 arch/m68k/configs/multi_defconfig    |   1 -
 arch/m68k/configs/mvme147_defconfig  |   1 -
 arch/m68k/configs/mvme16x_defconfig  |   1 -
 arch/m68k/configs/q40_defconfig      |   1 -
 arch/m68k/configs/sun3_defconfig     |   1 -
 arch/m68k/configs/sun3x_defconfig    |   1 -
 arch/s390/configs/debug_defconfig    |   1 -
 arch/s390/configs/defconfig          |   1 -
 block/bdev.c                         |   5 -
 fs/btrfs/extent_io.c                 |  10 -
 fs/btrfs/super.c                     |   2 -
 fs/ext4/readpage.c                   |   6 -
 fs/ext4/super.c                      |   3 -
 fs/f2fs/data.c                       |   7 -
 fs/mpage.c                           |   7 -
 fs/ntfs3/ntfs_fs.h                   |   1 -
 fs/ocfs2/super.c                     |   2 -
 fs/super.c                           |   3 -
 include/linux/cleancache.h           | 124 -----------
 include/linux/fs.h                   |   5 -
 mm/Kconfig                           |  22 --
 mm/Makefile                          |   1 -
 mm/cleancache.c                      | 315 ---------------------------
 mm/filemap.c                         |  11 -
 mm/truncate.c                        |  15 +-
 37 files changed, 4 insertions(+), 867 deletions(-)
 delete mode 100644 Documentation/vm/cleancache.rst
 delete mode 100644 include/linux/cleancache.h
 delete mode 100644 mm/cleancache.c

diff --git a/Documentation/vm/cleancache.rst b/Documentation/vm/cleancache.rst
deleted file mode 100644
index 68cba9131c318..0000000000000
--- a/Documentation/vm/cleancache.rst
+++ /dev/null
@@ -1,296 +0,0 @@
-.. _cleancache:
-
-==========
-Cleancache
-==========
-
-Motivation
-==========
-
-Cleancache is a new optional feature provided by the VFS layer that
-potentially dramatically increases page cache effectiveness for
-many workloads in many environments at a negligible cost.
-
-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 cleancache 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.
-
-Later, 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 of data is copied into the kernel
-and a disk access is avoided.
-
-Transcendent memory "drivers" for cleancache are currently implemented
-in Xen (using hypervisor memory) and zcache (using in-kernel compressed
-memory) and other implementations are in development.
-
-:ref:`FAQs <faq>` are included below.
-
-Implementation Overview
-=======================
-
-A cleancache "backend" that provides transcendent memory registers itself
-to the kernel's cleancache "frontend" by calling cleancache_register_ops,
-passing a pointer to a cleancache_ops structure with funcs set appropriately.
-The functions provided must conform to certain semantics as follows:
-
-Most important, cleancache is "ephemeral".  Pages which are copied into
-cleancache have an indefinite lifetime which is completely unknowable
-by the kernel and so may or may not still be in cleancache at any later time.
-Thus, as its name implies, cleancache is not suitable for dirty pages.
-Cleancache has complete discretion over what pages to preserve and what
-pages to discard and when.
-
-Mounting a cleancache-enabled filesystem should call "init_fs" to obtain a
-pool id which, if positive, must be saved in the filesystem's superblock;
-a negative return value indicates failure.  A "put_page" will copy a
-(presumably about-to-be-evicted) page into cleancache and associate it with
-the pool id, a file key, and a page index into the file.  (The combination
-of a pool id, a file key, and an index is sometimes called a "handle".)
-A "get_page" will copy the page, if found, from cleancache into kernel memory.
-An "invalidate_page" will ensure the page no longer is present in cleancache;
-an "invalidate_inode" will invalidate all pages associated with the specified
-file; and, when a filesystem is unmounted, an "invalidate_fs" will invalidate
-all pages in all files specified by the given pool id and also surrender
-the pool id.
-
-An "init_shared_fs", like init_fs, obtains a pool id but tells cleancache
-to treat the pool as shared using a 128-bit UUID as a key.  On systems
-that may run multiple kernels (such as hard partitioned or virtualized
-systems) that may share a clustered filesystem, and where cleancache
-may be shared among those kernels, calls to init_shared_fs that specify the
-same UUID will receive the same pool id, thus allowing the pages to
-be shared.  Note that any security requirements must be imposed outside
-of the kernel (e.g. by "tools" that control cleancache).  Or a
-cleancache implementation can simply disable shared_init by always
-returning a negative value.
-
-If a get_page is successful on a non-shared pool, the page is invalidated
-(thus making cleancache an "exclusive" cache).  On a shared pool, the page
-is NOT invalidated on a successful get_page so that it remains accessible to
-other sharers.  The kernel is responsible for ensuring coherency between
-cleancache (shared or not), the page cache, and the filesystem, using
-cleancache invalidate operations as required.
-
-Note that cleancache must enforce put-put-get coherency and get-get
-coherency.  For the former, if two puts are made to the same handle but
-with different data, say AAA by the first put and BBB by the second, a
-subsequent get can never return the stale data (AAA).  For get-get coherency,
-if a get for a given handle fails, subsequent gets for that handle will
-never succeed unless preceded by a successful put with that handle.
-
-Last, cleancache provides no SMP serialization guarantees; if two
-different Linux threads are simultaneously putting and invalidating a page
-with the same handle, the results are indeterminate.  Callers must
-lock the page to ensure serial behavior.
-
-Cleancache Performance Metrics
-==============================
-
-If properly configured, monitoring of cleancache is done via debugfs in
-the `/sys/kernel/debug/cleancache` directory.  The effectiveness of cleancache
-can be measured (across all filesystems) with:
-
-``succ_gets``
-	number of gets that were successful
-
-``failed_gets``
-	number of gets that failed
-
-``puts``
-	number of puts attempted (all "succeed")
-
-``invalidates``
-	number of invalidates attempted
-
-A backend implementation may provide additional metrics.
-
-.. _faq:
-
-FAQ
-===
-
-* Where's the value? (Andrew Morton)
-
-Cleancache provides a significant performance benefit to many workloads
-in many environments with negligible overhead by improving the
-effectiveness of the pagecache.  Clean pagecache pages are
-saved in transcendent memory (RAM that is otherwise not directly
-addressable to the kernel); fetching those pages later avoids "refaults"
-and thus disk reads.
-
-Cleancache (and its sister code "frontswap") provide interfaces for
-this transcendent memory (aka "tmem"), which conceptually lies between
-fast kernel-directly-addressable RAM and slower DMA/asynchronous devices.
-Disallowing direct kernel or userland reads/writes to tmem
-is ideal when data is transformed to a different form and size (such
-as with compression) or secretly moved (as might be useful for write-
-balancing for some RAM-like devices).  Evicted page-cache pages (and
-swap pages) are a great use for this kind of slower-than-RAM-but-much-
-faster-than-disk transcendent memory, and the cleancache (and frontswap)
-"page-object-oriented" specification provides a nice way to read and
-write -- and indirectly "name" -- the pages.
-
-In the virtual case, the whole point of virtualization is to statistically
-multiplex physical resources across the varying demands of multiple
-virtual machines.  This is really hard to do with RAM and efforts to
-do it well with no kernel change have essentially failed (except in some
-well-publicized special-case workloads).  Cleancache -- and frontswap --
-with a fairly small impact on the kernel, provide a huge amount
-of flexibility for more dynamic, flexible RAM multiplexing.
-Specifically, the Xen Transcendent Memory backend allows otherwise
-"fallow" hypervisor-owned RAM to not only be "time-shared" between multiple
-virtual machines, but the pages can be compressed and deduplicated to
-optimize RAM utilization.  And when guest OS's are induced to surrender
-underutilized RAM (e.g. with "self-ballooning"), page cache pages
-are the first to go, and cleancache allows those pages to be
-saved and reclaimed if overall host system memory conditions allow.
-
-And the identical interface used for cleancache can be used in
-physical systems as well.  The zcache driver acts as a memory-hungry
-device that stores pages of data in a compressed state.  And
-the proposed "RAMster" driver shares RAM across multiple physical
-systems.
-
-* Why does cleancache have its sticky fingers so deep inside the
-  filesystems and VFS? (Andrew Morton and Christoph Hellwig)
-
-The core hooks for cleancache in VFS are in most cases a single line
-and the minimum set are placed precisely where needed to maintain
-coherency (via cleancache_invalidate operations) between cleancache,
-the page cache, and disk.  All hooks compile into nothingness if
-cleancache is config'ed off and turn into a function-pointer-
-compare-to-NULL if config'ed on but no backend claims the ops
-functions, or to a compare-struct-element-to-negative if a
-backend claims the ops functions but a filesystem doesn't enable
-cleancache.
-
-Some filesystems are built entirely on top of VFS and the hooks
-in VFS are sufficient, so don't require an "init_fs" hook; the
-initial implementation of cleancache didn't provide this hook.
-But for some filesystems (such as btrfs), the VFS hooks are
-incomplete and one or more hooks in fs-specific code are required.
-And for some other filesystems, such as tmpfs, cleancache may
-be counterproductive.  So it seemed prudent to require a filesystem
-to "opt in" to use cleancache, which requires adding a hook in
-each filesystem.  Not all filesystems are supported by cleancache
-only because they haven't been tested.  The existing set should
-be sufficient to validate the concept, the opt-in approach means
-that untested filesystems are not affected, and the hooks in the
-existing filesystems should make it very easy to add more
-filesystems in the future.
-
-The total impact of the hooks to existing fs and mm files is only
-about 40 lines added (not counting comments and blank lines).
-
-* Why not make cleancache asynchronous and batched so it can more
-  easily interface with real devices with DMA instead of copying each
-  individual page? (Minchan Kim)
-
-The one-page-at-a-time copy semantics simplifies the implementation
-on both the frontend and backend and also allows the backend to
-do fancy things on-the-fly like page compression and
-page deduplication.  And since the data is "gone" (copied into/out
-of the pageframe) before the cleancache get/put call returns,
-a great deal of race conditions and potential coherency issues
-are avoided.  While the interface seems odd for a "real device"
-or for real kernel-addressable RAM, it makes perfect sense for
-transcendent memory.
-
-* Why is non-shared cleancache "exclusive"?  And where is the
-  page "invalidated" after a "get"? (Minchan Kim)
-
-The main reason is to free up space in transcendent memory and
-to avoid unnecessary cleancache_invalidate calls.  If you want inclusive,
-the page can be "put" immediately following the "get".  If
-put-after-get for inclusive becomes common, the interface could
-be easily extended to add a "get_no_invalidate" call.
-
-The invalidate is done by the cleancache backend implementation.
-
-* What's the performance impact?
-
-Performance analysis has been presented at OLS'09 and LCA'10.
-Briefly, performance gains can be significant on most workloads,
-especially when memory pressure is high (e.g. when RAM is
-overcommitted in a virtual workload); and because the hooks are
-invoked primarily in place of or in addition to a disk read/write,
-overhead is negligible even in worst case workloads.  Basically
-cleancache replaces I/O with memory-copy-CPU-overhead; on older
-single-core systems with slow memory-copy speeds, cleancache
-has little value, but in newer multicore machines, especially
-consolidated/virtualized machines, it has great value.
-
-* How do I add cleancache support for filesystem X? (Boaz Harrash)
-
-Filesystems that are well-behaved and conform to certain
-restrictions can utilize cleancache simply by making a call to
-cleancache_init_fs at mount time.  Unusual, misbehaving, or
-poorly layered filesystems must either add additional hooks
-and/or undergo extensive additional testing... or should just
-not enable the optional cleancache.
-
-Some points for a filesystem to consider:
-
-  - The FS should be block-device-based (e.g. a ram-based FS such
-    as tmpfs should not enable cleancache)
-  - To ensure coherency/correctness, the FS must ensure that all
-    file removal or truncation operations either go through VFS or
-    add hooks to do the equivalent cleancache "invalidate" operations
-  - To ensure coherency/correctness, either inode numbers must
-    be unique across the lifetime of the on-disk file OR the
-    FS must provide an "encode_fh" function.
-  - The FS must call the VFS superblock alloc and deactivate routines
-    or add hooks to do the equivalent cleancache calls done there.
-  - To maximize performance, all pages fetched from the FS should
-    go through the do_mpag_readpage routine or the FS should add
-    hooks to do the equivalent (cf. btrfs)
-  - Currently, the FS blocksize must be the same as PAGESIZE.  This
-    is not an architectural restriction, but no backends currently
-    support anything different.
-  - A clustered FS should invoke the "shared_init_fs" cleancache
-    hook to get best performance for some backends.
-
-* Why not use the KVA of the inode as the key? (Christoph Hellwig)
-
-If cleancache would use the inode virtual address instead of
-inode/filehandle, the pool id could be eliminated.  But, this
-won't work because cleancache retains pagecache data pages
-persistently even when the inode has been pruned from the
-inode unused list, and only invalidates the data page if the file
-gets removed/truncated.  So if cleancache used the inode kva,
-there would be potential coherency issues if/when the inode
-kva is reused for a different file.  Alternately, if cleancache
-invalidated the pages when the inode kva was freed, much of the value
-of cleancache would be lost because the cache of pages in cleanache
-is potentially much larger than the kernel pagecache and is most
-useful if the pages survive inode cache removal.
-
-* Why is a global variable required?
-
-The cleancache_enabled flag is checked in all of the frequently-used
-cleancache hooks.  The alternative is a function call to check a static
-variable. Since cleancache is enabled dynamically at runtime, systems
-that don't enable cleancache would suffer thousands (possibly
-tens-of-thousands) of unnecessary function calls per second.  So the
-global variable allows cleancache to be enabled by default at compile
-time, but have insignificant performance impact when cleancache remains
-disabled at runtime.
-
-* Does cleanache work with KVM?
-
-The memory model of KVM is sufficiently different that a cleancache
-backend may have less value for KVM.  This remains to be tested,
-especially in an overcommitted system.
-
-* Does cleancache work in userspace?  It sounds useful for
-  memory hungry caches like web browsers.  (Jamie Lokier)
-
-No plans yet, though we agree it sounds useful, at least for
-apps that bypass the page cache (e.g. O_DIRECT).
-
-Last updated: Dan Magenheimer, April 13 2011
diff --git a/Documentation/vm/frontswap.rst b/Documentation/vm/frontswap.rst
index 1979f430c1c5b..e2e5ab3e375e3 100644
--- a/Documentation/vm/frontswap.rst
+++ b/Documentation/vm/frontswap.rst
@@ -8,12 +8,6 @@ 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.
 
-(Note, frontswap -- and :ref:`cleancache` (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)
-
 .. _Transcendent memory in a nutshell: https://lwn.net/Articles/454795/
 
 Frontswap is so named because it can be thought of as the opposite of
@@ -87,11 +81,9 @@ This interface is ideal when data is transformed to a different form
 and size (such as with compression) or secretly moved (as might be
 useful for write-balancing for some RAM-like devices).  Swap pages (and
 evicted page-cache pages) are a great use for this kind of slower-than-RAM-
-but-much-faster-than-disk "pseudo-RAM device" and the frontswap (and
-cleancache) interface to transcendent memory provides a nice way to read
-and write -- and indirectly "name" -- the pages.
+but-much-faster-than-disk "pseudo-RAM device".
 
-Frontswap -- and cleancache -- with a fairly small impact on the kernel,
+Frontswap with a fairly small impact on the kernel,
 provides a huge amount of flexibility for more dynamic, flexible RAM
 utilization in various system configurations:
 
diff --git a/Documentation/vm/index.rst b/Documentation/vm/index.rst
index 932440805453e..44365c4574a37 100644
--- a/Documentation/vm/index.rst
+++ b/Documentation/vm/index.rst
@@ -15,7 +15,6 @@ algorithms.  If you are looking for advice on simply allocating memory, see the
    active_mm
    arch_pgtable_helpers
    balance
-   cleancache
    damon/index
    free_page_reporting
    frontswap
diff --git a/MAINTAINERS b/MAINTAINERS
index 35f0a1472bafa..9951a677c6d2e 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4683,13 +4683,6 @@ T:	git git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git for-next/cla
 F:	include/linux/cfi.h
 F:	kernel/cfi.c
 
-CLEANCACHE API
-M:	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
-L:	linux-kernel@vger.kernel.org
-S:	Maintained
-F:	include/linux/cleancache.h
-F:	mm/cleancache.c
-
 CLK API
 M:	Russell King <linux@armlinux.org.uk>
 L:	linux-clk@vger.kernel.org
diff --git a/arch/arm/configs/bcm2835_defconfig b/arch/arm/configs/bcm2835_defconfig
index 383c632eba7bd..a9ed79b7f8716 100644
--- a/arch/arm/configs/bcm2835_defconfig
+++ b/arch/arm/configs/bcm2835_defconfig
@@ -31,7 +31,6 @@ CONFIG_ARCH_BCM2835=y
 CONFIG_PREEMPT_VOLUNTARY=y
 CONFIG_AEABI=y
 CONFIG_KSM=y
-CONFIG_CLEANCACHE=y
 CONFIG_CMA=y
 CONFIG_SECCOMP=y
 CONFIG_KEXEC=y
diff --git a/arch/arm/configs/qcom_defconfig b/arch/arm/configs/qcom_defconfig
index 0daa9c0d298e7..9981566f20961 100644
--- a/arch/arm/configs/qcom_defconfig
+++ b/arch/arm/configs/qcom_defconfig
@@ -27,7 +27,6 @@ CONFIG_PCIE_QCOM=y
 CONFIG_SMP=y
 CONFIG_PREEMPT=y
 CONFIG_HIGHMEM=y
-CONFIG_CLEANCACHE=y
 CONFIG_ARM_APPENDED_DTB=y
 CONFIG_ARM_ATAG_DTB_COMPAT=y
 CONFIG_CPU_IDLE=y
diff --git a/arch/m68k/configs/amiga_defconfig b/arch/m68k/configs/amiga_defconfig
index e2b14ea993423..c3173bdd394e9 100644
--- a/arch/m68k/configs/amiga_defconfig
+++ b/arch/m68k/configs/amiga_defconfig
@@ -45,7 +45,6 @@ CONFIG_IOSCHED_BFQ=m
 CONFIG_BINFMT_AOUT=m
 CONFIG_BINFMT_MISC=m
 # CONFIG_COMPACTION is not set
-CONFIG_CLEANCACHE=y
 CONFIG_ZPOOL=m
 CONFIG_NET=y
 CONFIG_PACKET=y
diff --git a/arch/m68k/configs/apollo_defconfig b/arch/m68k/configs/apollo_defconfig
index 41f3f3b738b3e..4900fa2f3580b 100644
--- a/arch/m68k/configs/apollo_defconfig
+++ b/arch/m68k/configs/apollo_defconfig
@@ -41,7 +41,6 @@ CONFIG_IOSCHED_BFQ=m
 CONFIG_BINFMT_AOUT=m
 CONFIG_BINFMT_MISC=m
 # CONFIG_COMPACTION is not set
-CONFIG_CLEANCACHE=y
 CONFIG_ZPOOL=m
 CONFIG_NET=y
 CONFIG_PACKET=y
diff --git a/arch/m68k/configs/atari_defconfig b/arch/m68k/configs/atari_defconfig
index 3fd0ea135886b..d6e243023390f 100644
--- a/arch/m68k/configs/atari_defconfig
+++ b/arch/m68k/configs/atari_defconfig
@@ -48,7 +48,6 @@ CONFIG_IOSCHED_BFQ=m
 CONFIG_BINFMT_AOUT=m
 CONFIG_BINFMT_MISC=m
 # CONFIG_COMPACTION is not set
-CONFIG_CLEANCACHE=y
 CONFIG_ZPOOL=m
 CONFIG_NET=y
 CONFIG_PACKET=y
diff --git a/arch/m68k/configs/bvme6000_defconfig b/arch/m68k/configs/bvme6000_defconfig
index 11a19f87e5864..4755f97a21835 100644
--- a/arch/m68k/configs/bvme6000_defconfig
+++ b/arch/m68k/configs/bvme6000_defconfig
@@ -38,7 +38,6 @@ CONFIG_IOSCHED_BFQ=m
 CONFIG_BINFMT_AOUT=m
 CONFIG_BINFMT_MISC=m
 # CONFIG_COMPACTION is not set
-CONFIG_CLEANCACHE=y
 CONFIG_ZPOOL=m
 CONFIG_NET=y
 CONFIG_PACKET=y
diff --git a/arch/m68k/configs/hp300_defconfig b/arch/m68k/configs/hp300_defconfig
index ee981271476a8..8c68178c6ae15 100644
--- a/arch/m68k/configs/hp300_defconfig
+++ b/arch/m68k/configs/hp300_defconfig
@@ -40,7 +40,6 @@ CONFIG_IOSCHED_BFQ=m
 CONFIG_BINFMT_AOUT=m
 CONFIG_BINFMT_MISC=m
 # CONFIG_COMPACTION is not set
-CONFIG_CLEANCACHE=y
 CONFIG_ZPOOL=m
 CONFIG_NET=y
 CONFIG_PACKET=y
diff --git a/arch/m68k/configs/mac_defconfig b/arch/m68k/configs/mac_defconfig
index a48656d328dd1..ddc492ced755c 100644
--- a/arch/m68k/configs/mac_defconfig
+++ b/arch/m68k/configs/mac_defconfig
@@ -39,7 +39,6 @@ CONFIG_IOSCHED_BFQ=m
 CONFIG_BINFMT_AOUT=m
 CONFIG_BINFMT_MISC=m
 # CONFIG_COMPACTION is not set
-CONFIG_CLEANCACHE=y
 CONFIG_ZPOOL=m
 CONFIG_NET=y
 CONFIG_PACKET=y
diff --git a/arch/m68k/configs/multi_defconfig b/arch/m68k/configs/multi_defconfig
index b9b7a5cc6a1e6..6b1651eb27499 100644
--- a/arch/m68k/configs/multi_defconfig
+++ b/arch/m68k/configs/multi_defconfig
@@ -59,7 +59,6 @@ CONFIG_IOSCHED_BFQ=m
 CONFIG_BINFMT_AOUT=m
 CONFIG_BINFMT_MISC=m
 # CONFIG_COMPACTION is not set
-CONFIG_CLEANCACHE=y
 CONFIG_ZPOOL=m
 CONFIG_NET=y
 CONFIG_PACKET=y
diff --git a/arch/m68k/configs/mvme147_defconfig b/arch/m68k/configs/mvme147_defconfig
index 3887b1c9c5fdc..2fc003520753a 100644
--- a/arch/m68k/configs/mvme147_defconfig
+++ b/arch/m68k/configs/mvme147_defconfig
@@ -37,7 +37,6 @@ CONFIG_IOSCHED_BFQ=m
 CONFIG_BINFMT_AOUT=m
 CONFIG_BINFMT_MISC=m
 # CONFIG_COMPACTION is not set
-CONFIG_CLEANCACHE=y
 CONFIG_ZPOOL=m
 CONFIG_NET=y
 CONFIG_PACKET=y
diff --git a/arch/m68k/configs/mvme16x_defconfig b/arch/m68k/configs/mvme16x_defconfig
index 19e5992bba6ca..44fd3c0a311b0 100644
--- a/arch/m68k/configs/mvme16x_defconfig
+++ b/arch/m68k/configs/mvme16x_defconfig
@@ -38,7 +38,6 @@ CONFIG_IOSCHED_BFQ=m
 CONFIG_BINFMT_AOUT=m
 CONFIG_BINFMT_MISC=m
 # CONFIG_COMPACTION is not set
-CONFIG_CLEANCACHE=y
 CONFIG_ZPOOL=m
 CONFIG_NET=y
 CONFIG_PACKET=y
diff --git a/arch/m68k/configs/q40_defconfig b/arch/m68k/configs/q40_defconfig
index af25efaa32967..695a92e10522e 100644
--- a/arch/m68k/configs/q40_defconfig
+++ b/arch/m68k/configs/q40_defconfig
@@ -39,7 +39,6 @@ CONFIG_IOSCHED_BFQ=m
 CONFIG_BINFMT_AOUT=m
 CONFIG_BINFMT_MISC=m
 # CONFIG_COMPACTION is not set
-CONFIG_CLEANCACHE=y
 CONFIG_ZPOOL=m
 CONFIG_NET=y
 CONFIG_PACKET=y
diff --git a/arch/m68k/configs/sun3_defconfig b/arch/m68k/configs/sun3_defconfig
index 14dd96d3f5efd..e655a9f5b6376 100644
--- a/arch/m68k/configs/sun3_defconfig
+++ b/arch/m68k/configs/sun3_defconfig
@@ -35,7 +35,6 @@ CONFIG_IOSCHED_BFQ=m
 CONFIG_BINFMT_AOUT=m
 CONFIG_BINFMT_MISC=m
 # CONFIG_COMPACTION is not set
-CONFIG_CLEANCACHE=y
 CONFIG_ZPOOL=m
 CONFIG_NET=y
 CONFIG_PACKET=y
diff --git a/arch/m68k/configs/sun3x_defconfig b/arch/m68k/configs/sun3x_defconfig
index 8ac2402ac334a..27193459defbf 100644
--- a/arch/m68k/configs/sun3x_defconfig
+++ b/arch/m68k/configs/sun3x_defconfig
@@ -35,7 +35,6 @@ CONFIG_IOSCHED_BFQ=m
 CONFIG_BINFMT_AOUT=m
 CONFIG_BINFMT_MISC=m
 # CONFIG_COMPACTION is not set
-CONFIG_CLEANCACHE=y
 CONFIG_ZPOOL=m
 CONFIG_NET=y
 CONFIG_PACKET=y
diff --git a/arch/s390/configs/debug_defconfig b/arch/s390/configs/debug_defconfig
index 354e51dcb3e27..7fe8975b49ece 100644
--- a/arch/s390/configs/debug_defconfig
+++ b/arch/s390/configs/debug_defconfig
@@ -96,7 +96,6 @@ CONFIG_MEMORY_HOTPLUG=y
 CONFIG_MEMORY_HOTREMOVE=y
 CONFIG_KSM=y
 CONFIG_TRANSPARENT_HUGEPAGE=y
-CONFIG_CLEANCACHE=y
 CONFIG_FRONTSWAP=y
 CONFIG_CMA_DEBUG=y
 CONFIG_CMA_DEBUGFS=y
diff --git a/arch/s390/configs/defconfig b/arch/s390/configs/defconfig
index 8dee6c3782f35..466780c465f53 100644
--- a/arch/s390/configs/defconfig
+++ b/arch/s390/configs/defconfig
@@ -91,7 +91,6 @@ CONFIG_MEMORY_HOTPLUG=y
 CONFIG_MEMORY_HOTREMOVE=y
 CONFIG_KSM=y
 CONFIG_TRANSPARENT_HUGEPAGE=y
-CONFIG_CLEANCACHE=y
 CONFIG_FRONTSWAP=y
 CONFIG_CMA_SYSFS=y
 CONFIG_CMA_AREAS=7
diff --git a/block/bdev.c b/block/bdev.c
index 8bf93a19041b7..102837a370517 100644
--- a/block/bdev.c
+++ b/block/bdev.c
@@ -24,7 +24,6 @@
 #include <linux/pseudo_fs.h>
 #include <linux/uio.h>
 #include <linux/namei.h>
-#include <linux/cleancache.h>
 #include <linux/part_stat.h>
 #include <linux/uaccess.h>
 #include "../fs/internal.h"
@@ -88,10 +87,6 @@ void invalidate_bdev(struct block_device *bdev)
 		lru_add_drain_all();	/* make sure all lru add caches are flushed */
 		invalidate_mapping_pages(mapping, 0, -1);
 	}
-	/* 99% of the time, we don't need to flush the cleancache on the bdev.
-	 * But, for the strange corners, lets be cautious
-	 */
-	cleancache_invalidate_inode(mapping);
 }
 EXPORT_SYMBOL(invalidate_bdev);
 
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 9234d96a7fd5c..b1299fd44cfeb 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -12,7 +12,6 @@
 #include <linux/writeback.h>
 #include <linux/pagevec.h>
 #include <linux/prefetch.h>
-#include <linux/cleancache.h>
 #include <linux/fsverity.h>
 #include "misc.h"
 #include "extent_io.h"
@@ -3583,15 +3582,6 @@ int btrfs_do_readpage(struct page *page, struct extent_map **em_cached,
 		goto out;
 	}
 
-	if (!PageUptodate(page)) {
-		if (cleancache_get_page(page) == 0) {
-			BUG_ON(blocksize != PAGE_SIZE);
-			unlock_extent(tree, start, end);
-			unlock_page(page);
-			goto out;
-		}
-	}
-
 	if (page->index == last_byte >> PAGE_SHIFT) {
 		size_t zero_offset = offset_in_page(last_byte);
 
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index a1c54a2c787c5..39f76b889bdf6 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -23,7 +23,6 @@
 #include <linux/miscdevice.h>
 #include <linux/magic.h>
 #include <linux/slab.h>
-#include <linux/cleancache.h>
 #include <linux/ratelimit.h>
 #include <linux/crc32c.h>
 #include <linux/btrfs.h>
@@ -1374,7 +1373,6 @@ static int btrfs_fill_super(struct super_block *sb,
 		goto fail_close;
 	}
 
-	cleancache_init_fs(sb);
 	sb->s_flags |= SB_ACTIVE;
 	return 0;
 
diff --git a/fs/ext4/readpage.c b/fs/ext4/readpage.c
index 3db9234035053..4cd62f1d848c8 100644
--- a/fs/ext4/readpage.c
+++ b/fs/ext4/readpage.c
@@ -43,7 +43,6 @@
 #include <linux/writeback.h>
 #include <linux/backing-dev.h>
 #include <linux/pagevec.h>
-#include <linux/cleancache.h>
 
 #include "ext4.h"
 
@@ -350,11 +349,6 @@ int ext4_mpage_readpages(struct inode *inode,
 		} else if (fully_mapped) {
 			SetPageMappedToDisk(page);
 		}
-		if (fully_mapped && blocks_per_page == 1 &&
-		    !PageUptodate(page) && cleancache_get_page(page) == 0) {
-			SetPageUptodate(page);
-			goto confused;
-		}
 
 		/*
 		 * This page will go to BIO.  Do we need to send this
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index b72d989b77fb6..b259343ebfc54 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -39,7 +39,6 @@
 #include <linux/log2.h>
 #include <linux/crc16.h>
 #include <linux/dax.h>
-#include <linux/cleancache.h>
 #include <linux/uaccess.h>
 #include <linux/iversion.h>
 #include <linux/unicode.h>
@@ -3141,8 +3140,6 @@ static int ext4_setup_super(struct super_block *sb, struct ext4_super_block *es,
 			EXT4_BLOCKS_PER_GROUP(sb),
 			EXT4_INODES_PER_GROUP(sb),
 			sbi->s_mount_opt, sbi->s_mount_opt2);
-
-	cleancache_init_fs(sb);
 	return err;
 }
 
diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 0a1d236212f85..d8e739d0eef37 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -18,7 +18,6 @@
 #include <linux/swap.h>
 #include <linux/prefetch.h>
 #include <linux/uio.h>
-#include <linux/cleancache.h>
 #include <linux/sched/signal.h>
 #include <linux/fiemap.h>
 #include <linux/iomap.h>
@@ -2035,12 +2034,6 @@ static int f2fs_read_single_page(struct inode *inode, struct page *page,
 		block_nr = map->m_pblk + block_in_file - map->m_lblk;
 		SetPageMappedToDisk(page);
 
-		if (!PageUptodate(page) && (!PageSwapCache(page) &&
-					!cleancache_get_page(page))) {
-			SetPageUptodate(page);
-			goto confused;
-		}
-
 		if (!f2fs_is_valid_blkaddr(F2FS_I_SB(inode), block_nr,
 						DATA_GENERIC_ENHANCE_READ)) {
 			ret = -EFSCORRUPTED;
diff --git a/fs/mpage.c b/fs/mpage.c
index 334e7d09aa652..87f5cfef6caa7 100644
--- a/fs/mpage.c
+++ b/fs/mpage.c
@@ -29,7 +29,6 @@
 #include <linux/writeback.h>
 #include <linux/backing-dev.h>
 #include <linux/pagevec.h>
-#include <linux/cleancache.h>
 #include "internal.h"
 
 /*
@@ -284,12 +283,6 @@ static struct bio *do_mpage_readpage(struct mpage_readpage_args *args)
 		SetPageMappedToDisk(page);
 	}
 
-	if (fully_mapped && blocks_per_page == 1 && !PageUptodate(page) &&
-	    cleancache_get_page(page) == 0) {
-		SetPageUptodate(page);
-		goto confused;
-	}
-
 	/*
 	 * This page will go to BIO.  Do we need to send this BIO off first?
 	 */
diff --git a/fs/ntfs3/ntfs_fs.h b/fs/ntfs3/ntfs_fs.h
index 8aaec7e0804ef..fb825059d4886 100644
--- a/fs/ntfs3/ntfs_fs.h
+++ b/fs/ntfs3/ntfs_fs.h
@@ -11,7 +11,6 @@
 
 #include <linux/blkdev.h>
 #include <linux/buffer_head.h>
-#include <linux/cleancache.h>
 #include <linux/fs.h>
 #include <linux/highmem.h>
 #include <linux/kernel.h>
diff --git a/fs/ocfs2/super.c b/fs/ocfs2/super.c
index 1286b88b6fa17..2772dec9dcea4 100644
--- a/fs/ocfs2/super.c
+++ b/fs/ocfs2/super.c
@@ -25,7 +25,6 @@
 #include <linux/mount.h>
 #include <linux/seq_file.h>
 #include <linux/quotaops.h>
-#include <linux/cleancache.h>
 #include <linux/signal.h>
 
 #define CREATE_TRACE_POINTS
@@ -2283,7 +2282,6 @@ static int ocfs2_initialize_super(struct super_block *sb,
 		mlog_errno(status);
 		goto bail;
 	}
-	cleancache_init_shared_fs(sb);
 
 	osb->ocfs2_wq = alloc_ordered_workqueue("ocfs2_wq", WQ_MEM_RECLAIM);
 	if (!osb->ocfs2_wq) {
diff --git a/fs/super.c b/fs/super.c
index 3bfc0f8fbd5bc..79aa179a1b081 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -31,7 +31,6 @@
 #include <linux/mutex.h>
 #include <linux/backing-dev.h>
 #include <linux/rculist_bl.h>
-#include <linux/cleancache.h>
 #include <linux/fscrypt.h>
 #include <linux/fsnotify.h>
 #include <linux/lockdep.h>
@@ -260,7 +259,6 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags,
 	s->s_time_gran = 1000000000;
 	s->s_time_min = TIME64_MIN;
 	s->s_time_max = TIME64_MAX;
-	s->cleancache_poolid = CLEANCACHE_NO_POOL;
 
 	s->s_shrink.seeks = DEFAULT_SEEKS;
 	s->s_shrink.scan_objects = super_cache_scan;
@@ -330,7 +328,6 @@ void deactivate_locked_super(struct super_block *s)
 {
 	struct file_system_type *fs = s->s_type;
 	if (atomic_dec_and_test(&s->s_active)) {
-		cleancache_invalidate_fs(s);
 		unregister_shrinker(&s->s_shrink);
 		fs->kill_sb(s);
 
diff --git a/include/linux/cleancache.h b/include/linux/cleancache.h
deleted file mode 100644
index 5f5730c1d324f..0000000000000
--- a/include/linux/cleancache.h
+++ /dev/null
@@ -1,124 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0 */
-#ifndef _LINUX_CLEANCACHE_H
-#define _LINUX_CLEANCACHE_H
-
-#include <linux/fs.h>
-#include <linux/exportfs.h>
-#include <linux/mm.h>
-
-#define CLEANCACHE_NO_POOL		-1
-#define CLEANCACHE_NO_BACKEND		-2
-#define CLEANCACHE_NO_BACKEND_SHARED	-3
-
-#define CLEANCACHE_KEY_MAX 6
-
-/*
- * cleancache requires every file with a page in cleancache to have a
- * unique key unless/until the file is removed/truncated.  For some
- * filesystems, the inode number is unique, but for "modern" filesystems
- * an exportable filehandle is required (see exportfs.h)
- */
-struct cleancache_filekey {
-	union {
-		ino_t ino;
-		__u32 fh[CLEANCACHE_KEY_MAX];
-		u32 key[CLEANCACHE_KEY_MAX];
-	} u;
-};
-
-struct cleancache_ops {
-	int (*init_fs)(size_t);
-	int (*init_shared_fs)(uuid_t *uuid, size_t);
-	int (*get_page)(int, struct cleancache_filekey,
-			pgoff_t, struct page *);
-	void (*put_page)(int, struct cleancache_filekey,
-			pgoff_t, struct page *);
-	void (*invalidate_page)(int, struct cleancache_filekey, pgoff_t);
-	void (*invalidate_inode)(int, struct cleancache_filekey);
-	void (*invalidate_fs)(int);
-};
-
-extern int cleancache_register_ops(const struct cleancache_ops *ops);
-extern void __cleancache_init_fs(struct super_block *);
-extern void __cleancache_init_shared_fs(struct super_block *);
-extern int  __cleancache_get_page(struct page *);
-extern void __cleancache_put_page(struct page *);
-extern void __cleancache_invalidate_page(struct address_space *, struct page *);
-extern void __cleancache_invalidate_inode(struct address_space *);
-extern void __cleancache_invalidate_fs(struct super_block *);
-
-#ifdef CONFIG_CLEANCACHE
-#define cleancache_enabled (1)
-static inline bool cleancache_fs_enabled_mapping(struct address_space *mapping)
-{
-	return mapping->host->i_sb->cleancache_poolid >= 0;
-}
-static inline bool cleancache_fs_enabled(struct page *page)
-{
-	return cleancache_fs_enabled_mapping(page->mapping);
-}
-#else
-#define cleancache_enabled (0)
-#define cleancache_fs_enabled(_page) (0)
-#define cleancache_fs_enabled_mapping(_page) (0)
-#endif
-
-/*
- * The shim layer provided by these inline functions allows the compiler
- * to reduce all cleancache hooks to nothingness if CONFIG_CLEANCACHE
- * is disabled, to a single global variable check if CONFIG_CLEANCACHE
- * is enabled but no cleancache "backend" has dynamically enabled it,
- * and, for the most frequent cleancache ops, to a single global variable
- * check plus a superblock element comparison if CONFIG_CLEANCACHE is enabled
- * and a cleancache backend has dynamically enabled cleancache, but the
- * filesystem referenced by that cleancache op has not enabled cleancache.
- * As a result, CONFIG_CLEANCACHE can be enabled by default with essentially
- * no measurable performance impact.
- */
-
-static inline void cleancache_init_fs(struct super_block *sb)
-{
-	if (cleancache_enabled)
-		__cleancache_init_fs(sb);
-}
-
-static inline void cleancache_init_shared_fs(struct super_block *sb)
-{
-	if (cleancache_enabled)
-		__cleancache_init_shared_fs(sb);
-}
-
-static inline int cleancache_get_page(struct page *page)
-{
-	if (cleancache_enabled && cleancache_fs_enabled(page))
-		return __cleancache_get_page(page);
-	return -1;
-}
-
-static inline void cleancache_put_page(struct page *page)
-{
-	if (cleancache_enabled && cleancache_fs_enabled(page))
-		__cleancache_put_page(page);
-}
-
-static inline void cleancache_invalidate_page(struct address_space *mapping,
-					struct page *page)
-{
-	/* careful... page->mapping is NULL sometimes when this is called */
-	if (cleancache_enabled && cleancache_fs_enabled_mapping(mapping))
-		__cleancache_invalidate_page(mapping, page);
-}
-
-static inline void cleancache_invalidate_inode(struct address_space *mapping)
-{
-	if (cleancache_enabled && cleancache_fs_enabled_mapping(mapping))
-		__cleancache_invalidate_inode(mapping);
-}
-
-static inline void cleancache_invalidate_fs(struct super_block *sb)
-{
-	if (cleancache_enabled)
-		__cleancache_invalidate_fs(sb);
-}
-
-#endif /* _LINUX_CLEANCACHE_H */
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 45c69dae6b38c..0ec4d7742f5b2 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1535,11 +1535,6 @@ struct super_block {
 
 	const struct dentry_operations *s_d_op; /* default d_op for dentries */
 
-	/*
-	 * Saved pool identifier for cleancache (-1 means none)
-	 */
-	int cleancache_poolid;
-
 	struct shrinker s_shrink;	/* per-sb shrinker handle */
 
 	/* Number of inodes with nlink == 0 but still referenced */
diff --git a/mm/Kconfig b/mm/Kconfig
index a99bd499ef51d..430240289b02b 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -444,28 +444,6 @@ config USE_PERCPU_NUMA_NODE_ID
 config HAVE_SETUP_PER_CPU_AREA
 	bool
 
-config CLEANCACHE
-	bool "Enable cleancache driver to cache clean pages if tmem is present"
-	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
-	  cleancache 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
-
 config FRONTSWAP
 	bool "Enable frontswap to cache swap pages if tmem is present"
 	depends on SWAP
diff --git a/mm/Makefile b/mm/Makefile
index 588d3113f3b08..70d4309c9ce33 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -104,7 +104,6 @@ obj-$(CONFIG_DEBUG_KMEMLEAK) += kmemleak.o
 obj-$(CONFIG_DEBUG_RODATA_TEST) += rodata_test.o
 obj-$(CONFIG_DEBUG_VM_PGTABLE) += debug_vm_pgtable.o
 obj-$(CONFIG_PAGE_OWNER) += page_owner.o
-obj-$(CONFIG_CLEANCACHE) += cleancache.o
 obj-$(CONFIG_MEMORY_ISOLATION) += page_isolation.o
 obj-$(CONFIG_ZPOOL)	+= zpool.o
 obj-$(CONFIG_ZBUD)	+= zbud.o
diff --git a/mm/cleancache.c b/mm/cleancache.c
deleted file mode 100644
index db7eee9c08863..0000000000000
--- a/mm/cleancache.c
+++ /dev/null
@@ -1,315 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0-only
-/*
- * Cleancache frontend
- *
- * This code provides the generic "frontend" layer to call a matching
- * "backend" driver implementation of cleancache.  See
- * Documentation/vm/cleancache.rst for more information.
- *
- * Copyright (C) 2009-2010 Oracle Corp. All rights reserved.
- * Author: Dan Magenheimer
- */
-
-#include <linux/module.h>
-#include <linux/fs.h>
-#include <linux/exportfs.h>
-#include <linux/mm.h>
-#include <linux/debugfs.h>
-#include <linux/cleancache.h>
-
-/*
- * cleancache_ops is set by cleancache_register_ops to contain the pointers
- * to the cleancache "backend" implementation functions.
- */
-static const struct cleancache_ops *cleancache_ops __read_mostly;
-
-/*
- * Counters available via /sys/kernel/debug/cleancache (if debugfs is
- * properly configured.  These are for information only so are not protected
- * against increment races.
- */
-static u64 cleancache_succ_gets;
-static u64 cleancache_failed_gets;
-static u64 cleancache_puts;
-static u64 cleancache_invalidates;
-
-static void cleancache_register_ops_sb(struct super_block *sb, void *unused)
-{
-	switch (sb->cleancache_poolid) {
-	case CLEANCACHE_NO_BACKEND:
-		__cleancache_init_fs(sb);
-		break;
-	case CLEANCACHE_NO_BACKEND_SHARED:
-		__cleancache_init_shared_fs(sb);
-		break;
-	}
-}
-
-/*
- * Register operations for cleancache. Returns 0 on success.
- */
-int cleancache_register_ops(const struct cleancache_ops *ops)
-{
-	if (cmpxchg(&cleancache_ops, NULL, ops))
-		return -EBUSY;
-
-	/*
-	 * A cleancache backend can be built as a module and hence loaded after
-	 * a cleancache enabled filesystem has called cleancache_init_fs. To
-	 * handle such a scenario, here we call ->init_fs or ->init_shared_fs
-	 * for each active super block. To differentiate between local and
-	 * shared filesystems, we temporarily initialize sb->cleancache_poolid
-	 * to CLEANCACHE_NO_BACKEND or CLEANCACHE_NO_BACKEND_SHARED
-	 * respectively in case there is no backend registered at the time
-	 * cleancache_init_fs or cleancache_init_shared_fs is called.
-	 *
-	 * Since filesystems can be mounted concurrently with cleancache
-	 * backend registration, we have to be careful to guarantee that all
-	 * cleancache enabled filesystems that has been mounted by the time
-	 * cleancache_register_ops is called has got and all mounted later will
-	 * get cleancache_poolid. This is assured by the following statements
-	 * tied together:
-	 *
-	 * a) iterate_supers skips only those super blocks that has started
-	 *    ->kill_sb
-	 *
-	 * b) if iterate_supers encounters a super block that has not finished
-	 *    ->mount yet, it waits until it is finished
-	 *
-	 * c) cleancache_init_fs is called from ->mount and
-	 *    cleancache_invalidate_fs is called from ->kill_sb
-	 *
-	 * d) we call iterate_supers after cleancache_ops has been set
-	 *
-	 * From a) it follows that if iterate_supers skips a super block, then
-	 * either the super block is already dead, in which case we do not need
-	 * to bother initializing cleancache for it, or it was mounted after we
-	 * initiated iterate_supers. In the latter case, it must have seen
-	 * cleancache_ops set according to d) and initialized cleancache from
-	 * ->mount by itself according to c). This proves that we call
-	 * ->init_fs at least once for each active super block.
-	 *
-	 * From b) and c) it follows that if iterate_supers encounters a super
-	 * block that has already started ->init_fs, it will wait until ->mount
-	 * and hence ->init_fs has finished, then check cleancache_poolid, see
-	 * that it has already been set and therefore do nothing. This proves
-	 * that we call ->init_fs no more than once for each super block.
-	 *
-	 * Combined together, the last two paragraphs prove the function
-	 * correctness.
-	 *
-	 * Note that various cleancache callbacks may proceed before this
-	 * function is called or even concurrently with it, but since
-	 * CLEANCACHE_NO_BACKEND is negative, they will all result in a noop
-	 * until the corresponding ->init_fs has been actually called and
-	 * cleancache_ops has been set.
-	 */
-	iterate_supers(cleancache_register_ops_sb, NULL);
-	return 0;
-}
-EXPORT_SYMBOL(cleancache_register_ops);
-
-/* Called by a cleancache-enabled filesystem at time of mount */
-void __cleancache_init_fs(struct super_block *sb)
-{
-	int pool_id = CLEANCACHE_NO_BACKEND;
-
-	if (cleancache_ops) {
-		pool_id = cleancache_ops->init_fs(PAGE_SIZE);
-		if (pool_id < 0)
-			pool_id = CLEANCACHE_NO_POOL;
-	}
-	sb->cleancache_poolid = pool_id;
-}
-EXPORT_SYMBOL(__cleancache_init_fs);
-
-/* Called by a cleancache-enabled clustered filesystem at time of mount */
-void __cleancache_init_shared_fs(struct super_block *sb)
-{
-	int pool_id = CLEANCACHE_NO_BACKEND_SHARED;
-
-	if (cleancache_ops) {
-		pool_id = cleancache_ops->init_shared_fs(&sb->s_uuid, PAGE_SIZE);
-		if (pool_id < 0)
-			pool_id = CLEANCACHE_NO_POOL;
-	}
-	sb->cleancache_poolid = pool_id;
-}
-EXPORT_SYMBOL(__cleancache_init_shared_fs);
-
-/*
- * If the filesystem uses exportable filehandles, use the filehandle as
- * the key, else use the inode number.
- */
-static int cleancache_get_key(struct inode *inode,
-			      struct cleancache_filekey *key)
-{
-	int (*fhfn)(struct inode *, __u32 *fh, int *, struct inode *);
-	int len = 0, maxlen = CLEANCACHE_KEY_MAX;
-	struct super_block *sb = inode->i_sb;
-
-	key->u.ino = inode->i_ino;
-	if (sb->s_export_op != NULL) {
-		fhfn = sb->s_export_op->encode_fh;
-		if  (fhfn) {
-			len = (*fhfn)(inode, &key->u.fh[0], &maxlen, NULL);
-			if (len <= FILEID_ROOT || len == FILEID_INVALID)
-				return -1;
-			if (maxlen > CLEANCACHE_KEY_MAX)
-				return -1;
-		}
-	}
-	return 0;
-}
-
-/*
- * "Get" data from cleancache associated with the poolid/inode/index
- * that were specified when the data was put to cleanache and, if
- * successful, use it to fill the specified page with data and return 0.
- * The pageframe is unchanged and returns -1 if the get fails.
- * Page must be locked by caller.
- *
- * The function has two checks before any action is taken - whether
- * a backend is registered and whether the sb->cleancache_poolid
- * is correct.
- */
-int __cleancache_get_page(struct page *page)
-{
-	int ret = -1;
-	int pool_id;
-	struct cleancache_filekey key = { .u.key = { 0 } };
-
-	if (!cleancache_ops) {
-		cleancache_failed_gets++;
-		goto out;
-	}
-
-	VM_BUG_ON_PAGE(!PageLocked(page), page);
-	pool_id = page->mapping->host->i_sb->cleancache_poolid;
-	if (pool_id < 0)
-		goto out;
-
-	if (cleancache_get_key(page->mapping->host, &key) < 0)
-		goto out;
-
-	ret = cleancache_ops->get_page(pool_id, key, page->index, page);
-	if (ret == 0)
-		cleancache_succ_gets++;
-	else
-		cleancache_failed_gets++;
-out:
-	return ret;
-}
-EXPORT_SYMBOL(__cleancache_get_page);
-
-/*
- * "Put" data from a page to cleancache and associate it with the
- * (previously-obtained per-filesystem) poolid and the page's,
- * inode and page index.  Page must be locked.  Note that a put_page
- * always "succeeds", though a subsequent get_page may succeed or fail.
- *
- * The function has two checks before any action is taken - whether
- * a backend is registered and whether the sb->cleancache_poolid
- * is correct.
- */
-void __cleancache_put_page(struct page *page)
-{
-	int pool_id;
-	struct cleancache_filekey key = { .u.key = { 0 } };
-
-	if (!cleancache_ops) {
-		cleancache_puts++;
-		return;
-	}
-
-	VM_BUG_ON_PAGE(!PageLocked(page), page);
-	pool_id = page->mapping->host->i_sb->cleancache_poolid;
-	if (pool_id >= 0 &&
-		cleancache_get_key(page->mapping->host, &key) >= 0) {
-		cleancache_ops->put_page(pool_id, key, page->index, page);
-		cleancache_puts++;
-	}
-}
-EXPORT_SYMBOL(__cleancache_put_page);
-
-/*
- * Invalidate any data from cleancache associated with the poolid and the
- * page's inode and page index so that a subsequent "get" will fail.
- *
- * The function has two checks before any action is taken - whether
- * a backend is registered and whether the sb->cleancache_poolid
- * is correct.
- */
-void __cleancache_invalidate_page(struct address_space *mapping,
-					struct page *page)
-{
-	/* careful... page->mapping is NULL sometimes when this is called */
-	int pool_id = mapping->host->i_sb->cleancache_poolid;
-	struct cleancache_filekey key = { .u.key = { 0 } };
-
-	if (!cleancache_ops)
-		return;
-
-	if (pool_id >= 0) {
-		VM_BUG_ON_PAGE(!PageLocked(page), page);
-		if (cleancache_get_key(mapping->host, &key) >= 0) {
-			cleancache_ops->invalidate_page(pool_id,
-					key, page->index);
-			cleancache_invalidates++;
-		}
-	}
-}
-EXPORT_SYMBOL(__cleancache_invalidate_page);
-
-/*
- * Invalidate all data from cleancache associated with the poolid and the
- * mappings's inode so that all subsequent gets to this poolid/inode
- * will fail.
- *
- * The function has two checks before any action is taken - whether
- * a backend is registered and whether the sb->cleancache_poolid
- * is correct.
- */
-void __cleancache_invalidate_inode(struct address_space *mapping)
-{
-	int pool_id = mapping->host->i_sb->cleancache_poolid;
-	struct cleancache_filekey key = { .u.key = { 0 } };
-
-	if (!cleancache_ops)
-		return;
-
-	if (pool_id >= 0 && cleancache_get_key(mapping->host, &key) >= 0)
-		cleancache_ops->invalidate_inode(pool_id, key);
-}
-EXPORT_SYMBOL(__cleancache_invalidate_inode);
-
-/*
- * Called by any cleancache-enabled filesystem at time of unmount;
- * note that pool_id is surrendered and may be returned by a subsequent
- * cleancache_init_fs or cleancache_init_shared_fs.
- */
-void __cleancache_invalidate_fs(struct super_block *sb)
-{
-	int pool_id;
-
-	pool_id = sb->cleancache_poolid;
-	sb->cleancache_poolid = CLEANCACHE_NO_POOL;
-
-	if (cleancache_ops && pool_id >= 0)
-		cleancache_ops->invalidate_fs(pool_id);
-}
-EXPORT_SYMBOL(__cleancache_invalidate_fs);
-
-static int __init init_cleancache(void)
-{
-#ifdef CONFIG_DEBUG_FS
-	struct dentry *root = debugfs_create_dir("cleancache", NULL);
-
-	debugfs_create_u64("succ_gets", 0444, root, &cleancache_succ_gets);
-	debugfs_create_u64("failed_gets", 0444, root, &cleancache_failed_gets);
-	debugfs_create_u64("puts", 0444, root, &cleancache_puts);
-	debugfs_create_u64("invalidates", 0444, root, &cleancache_invalidates);
-#endif
-	return 0;
-}
-module_init(init_cleancache)
diff --git a/mm/filemap.c b/mm/filemap.c
index 6400b5dfe0a48..0d061a7c18f5a 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -35,7 +35,6 @@
 #include <linux/cpuset.h>
 #include <linux/hugetlb.h>
 #include <linux/memcontrol.h>
-#include <linux/cleancache.h>
 #include <linux/shmem_fs.h>
 #include <linux/rmap.h>
 #include <linux/delayacct.h>
@@ -151,16 +150,6 @@ static void filemap_unaccount_folio(struct address_space *mapping,
 {
 	long nr;
 
-	/*
-	 * if we're uptodate, flush out into the cleancache, otherwise
-	 * invalidate any existing cleancache entries.  We can't leave
-	 * stale data around in the cleancache once our page is gone
-	 */
-	if (folio_test_uptodate(folio) && folio_test_mappedtodisk(folio))
-		cleancache_put_page(&folio->page);
-	else
-		cleancache_invalidate_page(mapping, &folio->page);
-
 	VM_BUG_ON_FOLIO(folio_mapped(folio), folio);
 	if (!IS_ENABLED(CONFIG_DEBUG_VM) && unlikely(folio_mapped(folio))) {
 		int mapcount;
diff --git a/mm/truncate.c b/mm/truncate.c
index 3ddd170a6bf1f..d0e928a254880 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -22,7 +22,6 @@
 #include <linux/buffer_head.h>	/* grr. try_to_release_page,
 				   do_invalidatepage */
 #include <linux/shmem_fs.h>
-#include <linux/cleancache.h>
 #include <linux/rmap.h>
 #include "internal.h"
 
@@ -264,7 +263,6 @@ bool truncate_inode_partial_folio(struct folio *folio, loff_t start, loff_t end)
 	 */
 	folio_zero_range(folio, offset, length);
 
-	cleancache_invalidate_page(folio->mapping, &folio->page);
 	if (folio_has_private(folio))
 		do_invalidatepage(&folio->page, offset, length);
 	if (!folio_test_large(folio))
@@ -351,7 +349,7 @@ void truncate_inode_pages_range(struct address_space *mapping,
 	bool partial_end;
 
 	if (mapping_empty(mapping))
-		goto out;
+		return;
 
 	/*
 	 * 'start' and 'end' always covers the range of pages to be fully
@@ -443,9 +441,6 @@ void truncate_inode_pages_range(struct address_space *mapping,
 		folio_batch_release(&fbatch);
 		index++;
 	}
-
-out:
-	cleancache_invalidate_inode(mapping);
 }
 EXPORT_SYMBOL(truncate_inode_pages_range);
 
@@ -499,10 +494,6 @@ void truncate_inode_pages_final(struct address_space *mapping)
 		xa_unlock_irq(&mapping->i_pages);
 	}
 
-	/*
-	 * Cleancache needs notification even if there are no pages or shadow
-	 * entries.
-	 */
 	truncate_inode_pages(mapping, 0);
 }
 EXPORT_SYMBOL(truncate_inode_pages_final);
@@ -662,7 +653,7 @@ int invalidate_inode_pages2_range(struct address_space *mapping,
 	int did_range_unmap = 0;
 
 	if (mapping_empty(mapping))
-		goto out;
+		return 0;
 
 	folio_batch_init(&fbatch);
 	index = start;
@@ -726,8 +717,6 @@ int invalidate_inode_pages2_range(struct address_space *mapping,
 	if (dax_mapping(mapping)) {
 		unmap_mapping_pages(mapping, start, end - start + 1, false);
 	}
-out:
-	cleancache_invalidate_inode(mapping);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(invalidate_inode_pages2_range);
-- 
2.30.2

[PATCH 02/13] frontswap: remove frontswap_writethrough

[Christoph Hellwig]

frontswap_writethrough is never called, so remove it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 Documentation/vm/frontswap.rst |  6 ------
 include/linux/frontswap.h      |  1 -
 mm/frontswap.c                 | 23 +----------------------
 3 files changed, 1 insertion(+), 29 deletions(-)

diff --git a/Documentation/vm/frontswap.rst b/Documentation/vm/frontswap.rst
index e2e5ab3e375e3..2ab660651d04e 100644
--- a/Documentation/vm/frontswap.rst
+++ b/Documentation/vm/frontswap.rst
@@ -39,12 +39,6 @@ a disk write and, if the data is later read back, a disk read are avoided.
 If a store returns failure, transcendent memory has rejected the data, and the
 page can be written to swap as usual.
 
-If a backend chooses, frontswap can be configured as a "writethrough
-cache" by calling frontswap_writethrough().  In this mode, the reduction
-in swap device writes is lost (and also a non-trivial performance advantage)
-in order to allow the backend to arbitrarily "reclaim" space used to
-store frontswap pages to more completely manage its memory usage.
-
 Note that if a page is stored and the page already exists in transcendent memory
 (a "duplicate" store), either the store succeeds and the data is overwritten,
 or the store fails AND the page is invalidated.  This ensures stale data may
diff --git a/include/linux/frontswap.h b/include/linux/frontswap.h
index b07d88c92bb29..4a03fda415725 100644
--- a/include/linux/frontswap.h
+++ b/include/linux/frontswap.h
@@ -26,7 +26,6 @@ struct frontswap_ops {
 extern void frontswap_register_ops(struct frontswap_ops *ops);
 extern void frontswap_shrink(unsigned long);
 extern unsigned long frontswap_curr_pages(void);
-extern void frontswap_writethrough(bool);
 #define FRONTSWAP_HAS_EXCLUSIVE_GETS
 extern void frontswap_tmem_exclusive_gets(bool);
 
diff --git a/mm/frontswap.c b/mm/frontswap.c
index 6bed12260dea7..51a662a839559 100644
--- a/mm/frontswap.c
+++ b/mm/frontswap.c
@@ -32,16 +32,6 @@ static struct frontswap_ops *frontswap_ops __read_mostly;
 #define for_each_frontswap_ops(ops)		\
 	for ((ops) = frontswap_ops; (ops); (ops) = (ops)->next)
 
-/*
- * If enabled, frontswap_store will return failure even on success.  As
- * a result, the swap subsystem will always write the page to swap, in
- * effect converting frontswap into a writethrough cache.  In this mode,
- * there is no direct reduction in swap writes, but a frontswap backend
- * can unilaterally "reclaim" any pages in use with no data loss, thus
- * providing increases control over maximum memory usage due to frontswap.
- */
-static bool frontswap_writethrough_enabled __read_mostly;
-
 /*
  * If enabled, the underlying tmem implementation is capable of doing
  * exclusive gets, so frontswap_load, on a successful tmem_get must
@@ -170,15 +160,6 @@ void frontswap_register_ops(struct frontswap_ops *ops)
 }
 EXPORT_SYMBOL(frontswap_register_ops);
 
-/*
- * Enable/disable frontswap writethrough (see above).
- */
-void frontswap_writethrough(bool enable)
-{
-	frontswap_writethrough_enabled = enable;
-}
-EXPORT_SYMBOL(frontswap_writethrough);
-
 /*
  * Enable/disable frontswap exclusive gets (see above).
  */
@@ -283,9 +264,7 @@ int __frontswap_store(struct page *page)
 	} else {
 		inc_frontswap_failed_stores();
 	}
-	if (frontswap_writethrough_enabled)
-		/* report failure so swap also writes to swap device */
-		ret = -1;
+
 	return ret;
 }
 EXPORT_SYMBOL(__frontswap_store);
-- 
2.30.2

[PATCH 03/13] frontswap: remove frontswap_tmem_exclusive_gets

[Christoph Hellwig]

frontswap_tmem_exclusive_gets is never called, so remove it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 include/linux/frontswap.h |  2 --
 mm/frontswap.c            | 23 +----------------------
 2 files changed, 1 insertion(+), 24 deletions(-)

diff --git a/include/linux/frontswap.h b/include/linux/frontswap.h
index 4a03fda415725..83a56392cc7f6 100644
--- a/include/linux/frontswap.h
+++ b/include/linux/frontswap.h
@@ -26,8 +26,6 @@ struct frontswap_ops {
 extern void frontswap_register_ops(struct frontswap_ops *ops);
 extern void frontswap_shrink(unsigned long);
 extern unsigned long frontswap_curr_pages(void);
-#define FRONTSWAP_HAS_EXCLUSIVE_GETS
-extern void frontswap_tmem_exclusive_gets(bool);
 
 extern bool __frontswap_test(struct swap_info_struct *, pgoff_t);
 extern void __frontswap_init(unsigned type, unsigned long *map);
diff --git a/mm/frontswap.c b/mm/frontswap.c
index 51a662a839559..dba7f087ee862 100644
--- a/mm/frontswap.c
+++ b/mm/frontswap.c
@@ -32,13 +32,6 @@ static struct frontswap_ops *frontswap_ops __read_mostly;
 #define for_each_frontswap_ops(ops)		\
 	for ((ops) = frontswap_ops; (ops); (ops) = (ops)->next)
 
-/*
- * If enabled, the underlying tmem implementation is capable of doing
- * exclusive gets, so frontswap_load, on a successful tmem_get must
- * mark the page as no longer in frontswap AND mark it dirty.
- */
-static bool frontswap_tmem_exclusive_gets_enabled __read_mostly;
-
 #ifdef CONFIG_DEBUG_FS
 /*
  * Counters available via /sys/kernel/debug/frontswap (if debugfs is
@@ -160,15 +153,6 @@ void frontswap_register_ops(struct frontswap_ops *ops)
 }
 EXPORT_SYMBOL(frontswap_register_ops);
 
-/*
- * Enable/disable frontswap exclusive gets (see above).
- */
-void frontswap_tmem_exclusive_gets(bool enable)
-{
-	frontswap_tmem_exclusive_gets_enabled = enable;
-}
-EXPORT_SYMBOL(frontswap_tmem_exclusive_gets);
-
 /*
  * Called when a swap device is swapon'd.
  */
@@ -296,13 +280,8 @@ int __frontswap_load(struct page *page)
 		if (!ret) /* successful load */
 			break;
 	}
-	if (ret == 0) {
+	if (ret == 0)
 		inc_frontswap_loads();
-		if (frontswap_tmem_exclusive_gets_enabled) {
-			SetPageDirty(page);
-			__frontswap_clear(sis, offset);
-		}
-	}
 	return ret;
 }
 EXPORT_SYMBOL(__frontswap_load);
-- 
2.30.2

[PATCH 04/13] frontswap: remove frontswap_shrink

[Christoph Hellwig]

frontswap_shrink is never called, so remove it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 Documentation/vm/frontswap.rst | 13 ------
 include/linux/frontswap.h      |  1 -
 mm/frontswap.c                 | 83 ----------------------------------
 3 files changed, 97 deletions(-)

diff --git a/Documentation/vm/frontswap.rst b/Documentation/vm/frontswap.rst
index 2ab660651d04e..feecc5e244778 100644
--- a/Documentation/vm/frontswap.rst
+++ b/Documentation/vm/frontswap.rst
@@ -255,19 +255,6 @@ the old data and ensure that it is no longer accessible.  Since the
 swap subsystem then writes the new data to the read swap device,
 this is the correct course of action to ensure coherency.
 
-* What is frontswap_shrink for?
-
-When the (non-frontswap) swap subsystem swaps out a page to a real
-swap device, that page is only taking up low-value pre-allocated disk
-space.  But if frontswap has placed a page in transcendent memory, that
-page may be taking up valuable real estate.  The frontswap_shrink
-routine allows code outside of the swap subsystem to force pages out
-of the memory managed by frontswap and back into kernel-addressable memory.
-For example, in RAMster, a "suction driver" thread will attempt
-to "repatriate" pages sent to a remote machine back to the local machine;
-this is driven using the frontswap_shrink mechanism when memory pressure
-subsides.
-
 * Why does the frontswap patch create the new include file swapfile.h?
 
 The frontswap code depends on some swap-subsystem-internal data
diff --git a/include/linux/frontswap.h b/include/linux/frontswap.h
index 83a56392cc7f6..d268d7bb65134 100644
--- a/include/linux/frontswap.h
+++ b/include/linux/frontswap.h
@@ -24,7 +24,6 @@ struct frontswap_ops {
 };
 
 extern void frontswap_register_ops(struct frontswap_ops *ops);
-extern void frontswap_shrink(unsigned long);
 extern unsigned long frontswap_curr_pages(void);
 
 extern bool __frontswap_test(struct swap_info_struct *, pgoff_t);
diff --git a/mm/frontswap.c b/mm/frontswap.c
index dba7f087ee862..a77ebba6101bd 100644
--- a/mm/frontswap.c
+++ b/mm/frontswap.c
@@ -341,89 +341,6 @@ static unsigned long __frontswap_curr_pages(void)
 	return totalpages;
 }
 
-static int __frontswap_unuse_pages(unsigned long total, unsigned long *unused,
-					int *swapid)
-{
-	int ret = -EINVAL;
-	struct swap_info_struct *si = NULL;
-	int si_frontswap_pages;
-	unsigned long total_pages_to_unuse = total;
-	unsigned long pages = 0, pages_to_unuse = 0;
-
-	assert_spin_locked(&swap_lock);
-	plist_for_each_entry(si, &swap_active_head, list) {
-		si_frontswap_pages = atomic_read(&si->frontswap_pages);
-		if (total_pages_to_unuse < si_frontswap_pages) {
-			pages = pages_to_unuse = total_pages_to_unuse;
-		} else {
-			pages = si_frontswap_pages;
-			pages_to_unuse = 0; /* unuse all */
-		}
-		/* ensure there is enough RAM to fetch pages from frontswap */
-		if (security_vm_enough_memory_mm(current->mm, pages)) {
-			ret = -ENOMEM;
-			continue;
-		}
-		vm_unacct_memory(pages);
-		*unused = pages_to_unuse;
-		*swapid = si->type;
-		ret = 0;
-		break;
-	}
-
-	return ret;
-}
-
-/*
- * Used to check if it's necessary and feasible to unuse pages.
- * Return 1 when nothing to do, 0 when need to shrink pages,
- * error code when there is an error.
- */
-static int __frontswap_shrink(unsigned long target_pages,
-				unsigned long *pages_to_unuse,
-				int *type)
-{
-	unsigned long total_pages = 0, total_pages_to_unuse;
-
-	assert_spin_locked(&swap_lock);
-
-	total_pages = __frontswap_curr_pages();
-	if (total_pages <= target_pages) {
-		/* Nothing to do */
-		*pages_to_unuse = 0;
-		return 1;
-	}
-	total_pages_to_unuse = total_pages - target_pages;
-	return __frontswap_unuse_pages(total_pages_to_unuse, pages_to_unuse, type);
-}
-
-/*
- * Frontswap, like a true swap device, may unnecessarily retain pages
- * under certain circumstances; "shrink" frontswap is essentially a
- * "partial swapoff" and works by calling try_to_unuse to attempt to
- * unuse enough frontswap pages to attempt to -- subject to memory
- * constraints -- reduce the number of pages in frontswap to the
- * number given in the parameter target_pages.
- */
-void frontswap_shrink(unsigned long target_pages)
-{
-	unsigned long pages_to_unuse = 0;
-	int type, ret;
-
-	/*
-	 * we don't want to hold swap_lock while doing a very
-	 * lengthy try_to_unuse, but swap_list may change
-	 * so restart scan from swap_active_head each time
-	 */
-	spin_lock(&swap_lock);
-	ret = __frontswap_shrink(target_pages, &pages_to_unuse, &type);
-	spin_unlock(&swap_lock);
-	if (ret == 0)
-		try_to_unuse(type, true, pages_to_unuse);
-	return;
-}
-EXPORT_SYMBOL(frontswap_shrink);
-
 /*
  * Count and return the number of frontswap pages across all
  * swap devices.  This is exported so that backend drivers can
-- 
2.30.2

[PATCH 05/13] frontswap: remove frontswap_curr_pages

[Christoph Hellwig]

frontswap_curr_pages is never called, so remove it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 include/linux/frontswap.h |  1 -
 mm/frontswap.c            | 28 ----------------------------
 2 files changed, 29 deletions(-)

diff --git a/include/linux/frontswap.h b/include/linux/frontswap.h
index d268d7bb65134..5205c2977b208 100644
--- a/include/linux/frontswap.h
+++ b/include/linux/frontswap.h
@@ -24,7 +24,6 @@ struct frontswap_ops {
 };
 
 extern void frontswap_register_ops(struct frontswap_ops *ops);
-extern unsigned long frontswap_curr_pages(void);
 
 extern bool __frontswap_test(struct swap_info_struct *, pgoff_t);
 extern void __frontswap_init(unsigned type, unsigned long *map);
diff --git a/mm/frontswap.c b/mm/frontswap.c
index a77ebba6101bd..af8f68d0e5cc0 100644
--- a/mm/frontswap.c
+++ b/mm/frontswap.c
@@ -330,34 +330,6 @@ void __frontswap_invalidate_area(unsigned type)
 }
 EXPORT_SYMBOL(__frontswap_invalidate_area);
 
-static unsigned long __frontswap_curr_pages(void)
-{
-	unsigned long totalpages = 0;
-	struct swap_info_struct *si = NULL;
-
-	assert_spin_locked(&swap_lock);
-	plist_for_each_entry(si, &swap_active_head, list)
-		totalpages += atomic_read(&si->frontswap_pages);
-	return totalpages;
-}
-
-/*
- * Count and return the number of frontswap pages across all
- * swap devices.  This is exported so that backend drivers can
- * determine current usage without reading debugfs.
- */
-unsigned long frontswap_curr_pages(void)
-{
-	unsigned long totalpages = 0;
-
-	spin_lock(&swap_lock);
-	totalpages = __frontswap_curr_pages();
-	spin_unlock(&swap_lock);
-
-	return totalpages;
-}
-EXPORT_SYMBOL(frontswap_curr_pages);
-
 static int __init init_frontswap(void)
 {
 #ifdef CONFIG_DEBUG_FS
-- 
2.30.2

[PATCH 06/13] frontswap: simplify frontswap_init

[Christoph Hellwig]

Just use IS_ENABLED() and remove the __frontswap_init indirection.
Also remove the unused export.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 include/linux/frontswap.h | 9 +--------
 mm/frontswap.c            | 3 +--
 mm/swapfile.c             | 3 ++-
 3 files changed, 4 insertions(+), 11 deletions(-)

diff --git a/include/linux/frontswap.h b/include/linux/frontswap.h
index 5205c2977b208..73d7beb44f2b7 100644
--- a/include/linux/frontswap.h
+++ b/include/linux/frontswap.h
@@ -26,7 +26,7 @@ struct frontswap_ops {
 extern void frontswap_register_ops(struct frontswap_ops *ops);
 
 extern bool __frontswap_test(struct swap_info_struct *, pgoff_t);
-extern void __frontswap_init(unsigned type, unsigned long *map);
+extern void frontswap_init(unsigned type, unsigned long *map);
 extern int __frontswap_store(struct page *page);
 extern int __frontswap_load(struct page *page);
 extern void __frontswap_invalidate_page(unsigned, pgoff_t);
@@ -107,11 +107,4 @@ static inline void frontswap_invalidate_area(unsigned type)
 		__frontswap_invalidate_area(type);
 }
 
-static inline void frontswap_init(unsigned type, unsigned long *map)
-{
-#ifdef CONFIG_FRONTSWAP
-	__frontswap_init(type, map);
-#endif
-}
-
 #endif /* _LINUX_FRONTSWAP_H */
diff --git a/mm/frontswap.c b/mm/frontswap.c
index af8f68d0e5cc0..132d6ad6d70b7 100644
--- a/mm/frontswap.c
+++ b/mm/frontswap.c
@@ -156,7 +156,7 @@ EXPORT_SYMBOL(frontswap_register_ops);
 /*
  * Called when a swap device is swapon'd.
  */
-void __frontswap_init(unsigned type, unsigned long *map)
+void frontswap_init(unsigned type, unsigned long *map)
 {
 	struct swap_info_struct *sis = swap_info[type];
 	struct frontswap_ops *ops;
@@ -179,7 +179,6 @@ void __frontswap_init(unsigned type, unsigned long *map)
 	for_each_frontswap_ops(ops)
 		ops->init(type);
 }
-EXPORT_SYMBOL(__frontswap_init);
 
 bool __frontswap_test(struct swap_info_struct *sis,
 				pgoff_t offset)
diff --git a/mm/swapfile.c b/mm/swapfile.c
index caa9f81a0d15f..df5930ccd93dd 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2463,7 +2463,8 @@ static void enable_swap_info(struct swap_info_struct *p, int prio,
 				struct swap_cluster_info *cluster_info,
 				unsigned long *frontswap_map)
 {
-	frontswap_init(p->type, frontswap_map);
+	if (IS_ENABLED(CONFIG_FRONTSWAP))
+		frontswap_init(p->type, frontswap_map);
 	spin_lock(&swap_lock);
 	spin_lock(&p->lock);
 	setup_swap_info(p, prio, swap_map, cluster_info);
-- 
2.30.2

[PATCH 07/13] frontswap: remove the frontswap exports

[Christoph Hellwig]

None of the frontswap API is called from modular code.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 mm/frontswap.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/mm/frontswap.c b/mm/frontswap.c
index 132d6ad6d70b7..42d554da53bbb 100644
--- a/mm/frontswap.c
+++ b/mm/frontswap.c
@@ -151,7 +151,6 @@ void frontswap_register_ops(struct frontswap_ops *ops)
 		}
 	}
 }
-EXPORT_SYMBOL(frontswap_register_ops);
 
 /*
  * Called when a swap device is swapon'd.
@@ -187,7 +186,6 @@ bool __frontswap_test(struct swap_info_struct *sis,
 		return test_bit(offset, sis->frontswap_map);
 	return false;
 }
-EXPORT_SYMBOL(__frontswap_test);
 
 static inline void __frontswap_set(struct swap_info_struct *sis,
 				   pgoff_t offset)
@@ -250,7 +248,6 @@ int __frontswap_store(struct page *page)
 
 	return ret;
 }
-EXPORT_SYMBOL(__frontswap_store);
 
 /*
  * "Get" data from frontswap associated with swaptype and offset that were
@@ -283,7 +280,6 @@ int __frontswap_load(struct page *page)
 		inc_frontswap_loads();
 	return ret;
 }
-EXPORT_SYMBOL(__frontswap_load);
 
 /*
  * Invalidate any data from frontswap associated with the specified swaptype
@@ -305,7 +301,6 @@ void __frontswap_invalidate_page(unsigned type, pgoff_t offset)
 	__frontswap_clear(sis, offset);
 	inc_frontswap_invalidates();
 }
-EXPORT_SYMBOL(__frontswap_invalidate_page);
 
 /*
  * Invalidate all data from frontswap associated with all offsets for the
@@ -327,7 +322,6 @@ void __frontswap_invalidate_area(unsigned type)
 	atomic_set(&sis->frontswap_pages, 0);
 	bitmap_zero(sis->frontswap_map, sis->max);
 }
-EXPORT_SYMBOL(__frontswap_invalidate_area);
 
 static int __init init_frontswap(void)
 {
-- 
2.30.2

[PATCH 08/13] mm: simplify try_to_unuse

[Christoph Hellwig]

Remove the unused frontswap and pages_to_unuse arguments, and mark
the function static now that the caller in frontswap is gone.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 include/linux/frontswap.h |  7 ----
 include/linux/shmem_fs.h  |  3 +-
 include/linux/swapfile.h  |  1 -
 mm/shmem.c                | 33 +++-------------
 mm/swapfile.c             | 83 +++++++++++----------------------------
 5 files changed, 30 insertions(+), 97 deletions(-)

diff --git a/include/linux/frontswap.h b/include/linux/frontswap.h
index 73d7beb44f2b7..a9817d4fa74c1 100644
--- a/include/linux/frontswap.h
+++ b/include/linux/frontswap.h
@@ -7,13 +7,6 @@
 #include <linux/bitops.h>
 #include <linux/jump_label.h>
 
-/*
- * Return code to denote that requested number of
- * frontswap pages are unused(moved to page cache).
- * Used in shmem_unuse and try_to_unuse.
- */
-#define FRONTSWAP_PAGES_UNUSED	2
-
 struct frontswap_ops {
 	void (*init)(unsigned); /* this swap type was just swapon'ed */
 	int (*store)(unsigned, pgoff_t, struct page *); /* store a page */
diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index 166158b6e917a..e65b80ed09e77 100644
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -83,8 +83,7 @@ extern void shmem_unlock_mapping(struct address_space *mapping);
 extern struct page *shmem_read_mapping_page_gfp(struct address_space *mapping,
 					pgoff_t index, gfp_t gfp_mask);
 extern void shmem_truncate_range(struct inode *inode, loff_t start, loff_t end);
-extern int shmem_unuse(unsigned int type, bool frontswap,
-		       unsigned long *fs_pages_to_unuse);
+int shmem_unuse(unsigned int type);
 
 extern bool shmem_is_huge(struct vm_area_struct *vma,
 			  struct inode *inode, pgoff_t index);
diff --git a/include/linux/swapfile.h b/include/linux/swapfile.h
index e06febf629788..809cd01ef2c57 100644
--- a/include/linux/swapfile.h
+++ b/include/linux/swapfile.h
@@ -9,7 +9,6 @@
 extern spinlock_t swap_lock;
 extern struct plist_head swap_active_head;
 extern struct swap_info_struct *swap_info[];
-extern int try_to_unuse(unsigned int, bool, unsigned long);
 extern unsigned long generic_max_swapfile_size(void);
 extern unsigned long max_swapfile_size(void);
 
diff --git a/mm/shmem.c b/mm/shmem.c
index eb0fd90011308..421b2459929a2 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -36,7 +36,6 @@
 #include <linux/uio.h>
 #include <linux/khugepaged.h>
 #include <linux/hugetlb.h>
-#include <linux/frontswap.h>
 #include <linux/fs_parser.h>
 #include <linux/swapfile.h>
 
@@ -1146,7 +1145,7 @@ static void shmem_evict_inode(struct inode *inode)
 static int shmem_find_swap_entries(struct address_space *mapping,
 				   pgoff_t start, unsigned int nr_entries,
 				   struct page **entries, pgoff_t *indices,
-				   unsigned int type, bool frontswap)
+				   unsigned int type)
 {
 	XA_STATE(xas, &mapping->i_pages, start);
 	struct page *page;
@@ -1167,9 +1166,6 @@ static int shmem_find_swap_entries(struct address_space *mapping,
 		entry = radix_to_swp_entry(page);
 		if (swp_type(entry) != type)
 			continue;
-		if (frontswap &&
-		    !frontswap_test(swap_info[type], swp_offset(entry)))
-			continue;
 
 		indices[ret] = xas.xa_index;
 		entries[ret] = page;
@@ -1222,26 +1218,20 @@ static int shmem_unuse_swap_entries(struct inode *inode, struct pagevec pvec,
 /*
  * If swap found in inode, free it and move page from swapcache to filecache.
  */
-static int shmem_unuse_inode(struct inode *inode, unsigned int type,
-			     bool frontswap, unsigned long *fs_pages_to_unuse)
+static int shmem_unuse_inode(struct inode *inode, unsigned int type)
 {
 	struct address_space *mapping = inode->i_mapping;
 	pgoff_t start = 0;
 	struct pagevec pvec;
 	pgoff_t indices[PAGEVEC_SIZE];
-	bool frontswap_partial = (frontswap && *fs_pages_to_unuse > 0);
 	int ret = 0;
 
 	pagevec_init(&pvec);
 	do {
 		unsigned int nr_entries = PAGEVEC_SIZE;
 
-		if (frontswap_partial && *fs_pages_to_unuse < PAGEVEC_SIZE)
-			nr_entries = *fs_pages_to_unuse;
-
 		pvec.nr = shmem_find_swap_entries(mapping, start, nr_entries,
-						  pvec.pages, indices,
-						  type, frontswap);
+						  pvec.pages, indices, type);
 		if (pvec.nr == 0) {
 			ret = 0;
 			break;
@@ -1251,14 +1241,6 @@ static int shmem_unuse_inode(struct inode *inode, unsigned int type,
 		if (ret < 0)
 			break;
 
-		if (frontswap_partial) {
-			*fs_pages_to_unuse -= ret;
-			if (*fs_pages_to_unuse == 0) {
-				ret = FRONTSWAP_PAGES_UNUSED;
-				break;
-			}
-		}
-
 		start = indices[pvec.nr - 1];
 	} while (true);
 
@@ -1270,8 +1252,7 @@ static int shmem_unuse_inode(struct inode *inode, unsigned int type,
  * device 'type' back into memory, so the swap device can be
  * unused.
  */
-int shmem_unuse(unsigned int type, bool frontswap,
-		unsigned long *fs_pages_to_unuse)
+int shmem_unuse(unsigned int type)
 {
 	struct shmem_inode_info *info, *next;
 	int error = 0;
@@ -1294,8 +1275,7 @@ int shmem_unuse(unsigned int type, bool frontswap,
 		atomic_inc(&info->stop_eviction);
 		mutex_unlock(&shmem_swaplist_mutex);
 
-		error = shmem_unuse_inode(&info->vfs_inode, type, frontswap,
-					  fs_pages_to_unuse);
+		error = shmem_unuse_inode(&info->vfs_inode, type);
 		cond_resched();
 
 		mutex_lock(&shmem_swaplist_mutex);
@@ -4009,8 +3989,7 @@ int __init shmem_init(void)
 	return 0;
 }
 
-int shmem_unuse(unsigned int type, bool frontswap,
-		unsigned long *fs_pages_to_unuse)
+int shmem_unuse(unsigned int type, unsigned long *fs_pages_to_unuse)
 {
 	return 0;
 }
diff --git a/mm/swapfile.c b/mm/swapfile.c
index df5930ccd93dd..82342c77791bb 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1923,8 +1923,7 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
 
 static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
 			unsigned long addr, unsigned long end,
-			unsigned int type, bool frontswap,
-			unsigned long *fs_pages_to_unuse)
+			unsigned int type)
 {
 	struct page *page;
 	swp_entry_t entry;
@@ -1945,9 +1944,6 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
 			continue;
 
 		offset = swp_offset(entry);
-		if (frontswap && !frontswap_test(si, offset))
-			continue;
-
 		pte_unmap(pte);
 		swap_map = &si->swap_map[offset];
 		page = lookup_swap_cache(entry, vma, addr);
@@ -1979,11 +1975,6 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
 		try_to_free_swap(page);
 		unlock_page(page);
 		put_page(page);
-
-		if (*fs_pages_to_unuse && !--(*fs_pages_to_unuse)) {
-			ret = FRONTSWAP_PAGES_UNUSED;
-			goto out;
-		}
 try_next:
 		pte = pte_offset_map(pmd, addr);
 	} while (pte++, addr += PAGE_SIZE, addr != end);
@@ -1996,8 +1987,7 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
 
 static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud,
 				unsigned long addr, unsigned long end,
-				unsigned int type, bool frontswap,
-				unsigned long *fs_pages_to_unuse)
+				unsigned int type)
 {
 	pmd_t *pmd;
 	unsigned long next;
@@ -2009,8 +1999,7 @@ static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud,
 		next = pmd_addr_end(addr, end);
 		if (pmd_none_or_trans_huge_or_clear_bad(pmd))
 			continue;
-		ret = unuse_pte_range(vma, pmd, addr, next, type,
-				      frontswap, fs_pages_to_unuse);
+		ret = unuse_pte_range(vma, pmd, addr, next, type);
 		if (ret)
 			return ret;
 	} while (pmd++, addr = next, addr != end);
@@ -2019,8 +2008,7 @@ static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud,
 
 static inline int unuse_pud_range(struct vm_area_struct *vma, p4d_t *p4d,
 				unsigned long addr, unsigned long end,
-				unsigned int type, bool frontswap,
-				unsigned long *fs_pages_to_unuse)
+				unsigned int type)
 {
 	pud_t *pud;
 	unsigned long next;
@@ -2031,8 +2019,7 @@ static inline int unuse_pud_range(struct vm_area_struct *vma, p4d_t *p4d,
 		next = pud_addr_end(addr, end);
 		if (pud_none_or_clear_bad(pud))
 			continue;
-		ret = unuse_pmd_range(vma, pud, addr, next, type,
-				      frontswap, fs_pages_to_unuse);
+		ret = unuse_pmd_range(vma, pud, addr, next, type);
 		if (ret)
 			return ret;
 	} while (pud++, addr = next, addr != end);
@@ -2041,8 +2028,7 @@ static inline int unuse_pud_range(struct vm_area_struct *vma, p4d_t *p4d,
 
 static inline int unuse_p4d_range(struct vm_area_struct *vma, pgd_t *pgd,
 				unsigned long addr, unsigned long end,
-				unsigned int type, bool frontswap,
-				unsigned long *fs_pages_to_unuse)
+				unsigned int type)
 {
 	p4d_t *p4d;
 	unsigned long next;
@@ -2053,16 +2039,14 @@ static inline int unuse_p4d_range(struct vm_area_struct *vma, pgd_t *pgd,
 		next = p4d_addr_end(addr, end);
 		if (p4d_none_or_clear_bad(p4d))
 			continue;
-		ret = unuse_pud_range(vma, p4d, addr, next, type,
-				      frontswap, fs_pages_to_unuse);
+		ret = unuse_pud_range(vma, p4d, addr, next, type);
 		if (ret)
 			return ret;
 	} while (p4d++, addr = next, addr != end);
 	return 0;
 }
 
-static int unuse_vma(struct vm_area_struct *vma, unsigned int type,
-		     bool frontswap, unsigned long *fs_pages_to_unuse)
+static int unuse_vma(struct vm_area_struct *vma, unsigned int type)
 {
 	pgd_t *pgd;
 	unsigned long addr, end, next;
@@ -2076,16 +2060,14 @@ static int unuse_vma(struct vm_area_struct *vma, unsigned int type,
 		next = pgd_addr_end(addr, end);
 		if (pgd_none_or_clear_bad(pgd))
 			continue;
-		ret = unuse_p4d_range(vma, pgd, addr, next, type,
-				      frontswap, fs_pages_to_unuse);
+		ret = unuse_p4d_range(vma, pgd, addr, next, type);
 		if (ret)
 			return ret;
 	} while (pgd++, addr = next, addr != end);
 	return 0;
 }
 
-static int unuse_mm(struct mm_struct *mm, unsigned int type,
-		    bool frontswap, unsigned long *fs_pages_to_unuse)
+static int unuse_mm(struct mm_struct *mm, unsigned int type)
 {
 	struct vm_area_struct *vma;
 	int ret = 0;
@@ -2093,8 +2075,7 @@ static int unuse_mm(struct mm_struct *mm, unsigned int type,
 	mmap_read_lock(mm);
 	for (vma = mm->mmap; vma; vma = vma->vm_next) {
 		if (vma->anon_vma) {
-			ret = unuse_vma(vma, type, frontswap,
-					fs_pages_to_unuse);
+			ret = unuse_vma(vma, type);
 			if (ret)
 				break;
 		}
@@ -2110,7 +2091,7 @@ static int unuse_mm(struct mm_struct *mm, unsigned int type,
  * if there are no inuse entries after prev till end of the map.
  */
 static unsigned int find_next_to_unuse(struct swap_info_struct *si,
-					unsigned int prev, bool frontswap)
+					unsigned int prev)
 {
 	unsigned int i;
 	unsigned char count;
@@ -2124,8 +2105,7 @@ static unsigned int find_next_to_unuse(struct swap_info_struct *si,
 	for (i = prev + 1; i < si->max; i++) {
 		count = READ_ONCE(si->swap_map[i]);
 		if (count && swap_count(count) != SWAP_MAP_BAD)
-			if (!frontswap || frontswap_test(si, i))
-				break;
+			break;
 		if ((i % LATENCY_LIMIT) == 0)
 			cond_resched();
 	}
@@ -2136,12 +2116,7 @@ static unsigned int find_next_to_unuse(struct swap_info_struct *si,
 	return i;
 }
 
-/*
- * If the boolean frontswap is true, only unuse pages_to_unuse pages;
- * pages_to_unuse==0 means all pages; ignored if frontswap is false
- */
-int try_to_unuse(unsigned int type, bool frontswap,
-		 unsigned long pages_to_unuse)
+static int try_to_unuse(unsigned int type)
 {
 	struct mm_struct *prev_mm;
 	struct mm_struct *mm;
@@ -2155,13 +2130,10 @@ int try_to_unuse(unsigned int type, bool frontswap,
 	if (!READ_ONCE(si->inuse_pages))
 		return 0;
 
-	if (!frontswap)
-		pages_to_unuse = 0;
-
 retry:
-	retval = shmem_unuse(type, frontswap, &pages_to_unuse);
+	retval = shmem_unuse(type);
 	if (retval)
-		goto out;
+		return retval;
 
 	prev_mm = &init_mm;
 	mmget(prev_mm);
@@ -2178,11 +2150,10 @@ int try_to_unuse(unsigned int type, bool frontswap,
 		spin_unlock(&mmlist_lock);
 		mmput(prev_mm);
 		prev_mm = mm;
-		retval = unuse_mm(mm, type, frontswap, &pages_to_unuse);
-
+		retval = unuse_mm(mm, type);
 		if (retval) {
 			mmput(prev_mm);
-			goto out;
+			return retval;
 		}
 
 		/*
@@ -2199,7 +2170,7 @@ int try_to_unuse(unsigned int type, bool frontswap,
 	i = 0;
 	while (READ_ONCE(si->inuse_pages) &&
 	       !signal_pending(current) &&
-	       (i = find_next_to_unuse(si, i, frontswap)) != 0) {
+	       (i = find_next_to_unuse(si, i)) != 0) {
 
 		entry = swp_entry(type, i);
 		page = find_get_page(swap_address_space(entry), i);
@@ -2217,14 +2188,6 @@ int try_to_unuse(unsigned int type, bool frontswap,
 		try_to_free_swap(page);
 		unlock_page(page);
 		put_page(page);
-
-		/*
-		 * For frontswap, we just need to unuse pages_to_unuse, if
-		 * it was specified. Need not check frontswap again here as
-		 * we already zeroed out pages_to_unuse if not frontswap.
-		 */
-		if (pages_to_unuse && --pages_to_unuse == 0)
-			goto out;
 	}
 
 	/*
@@ -2242,10 +2205,10 @@ int try_to_unuse(unsigned int type, bool frontswap,
 	if (READ_ONCE(si->inuse_pages)) {
 		if (!signal_pending(current))
 			goto retry;
-		retval = -EINTR;
+		return -EINTR;
 	}
-out:
-	return (retval == FRONTSWAP_PAGES_UNUSED) ? 0 : retval;
+
+	return 0;
 }
 
 /*
@@ -2577,7 +2540,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 	disable_swap_slots_cache_lock();
 
 	set_current_oom_origin();
-	err = try_to_unuse(p->type, false, 0); /* force unuse all pages */
+	err = try_to_unuse(p->type);
 	clear_current_oom_origin();
 
 	if (err) {
-- 
2.30.2

[PATCH 09/13] frontswap: remove frontswap_test

[Christoph Hellwig]

frontswap_test is unused now, remove it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 include/linux/frontswap.h | 11 -----------
 mm/frontswap.c            |  2 +-
 2 files changed, 1 insertion(+), 12 deletions(-)

diff --git a/include/linux/frontswap.h b/include/linux/frontswap.h
index a9817d4fa74c1..c5b2848d22404 100644
--- a/include/linux/frontswap.h
+++ b/include/linux/frontswap.h
@@ -18,7 +18,6 @@ struct frontswap_ops {
 
 extern void frontswap_register_ops(struct frontswap_ops *ops);
 
-extern bool __frontswap_test(struct swap_info_struct *, pgoff_t);
 extern void frontswap_init(unsigned type, unsigned long *map);
 extern int __frontswap_store(struct page *page);
 extern int __frontswap_load(struct page *page);
@@ -33,11 +32,6 @@ static inline bool frontswap_enabled(void)
 	return static_branch_unlikely(&frontswap_enabled_key);
 }
 
-static inline bool frontswap_test(struct swap_info_struct *sis, pgoff_t offset)
-{
-	return __frontswap_test(sis, offset);
-}
-
 static inline void frontswap_map_set(struct swap_info_struct *p,
 				     unsigned long *map)
 {
@@ -56,11 +50,6 @@ static inline bool frontswap_enabled(void)
 	return false;
 }
 
-static inline bool frontswap_test(struct swap_info_struct *sis, pgoff_t offset)
-{
-	return false;
-}
-
 static inline void frontswap_map_set(struct swap_info_struct *p,
 				     unsigned long *map)
 {
diff --git a/mm/frontswap.c b/mm/frontswap.c
index 42d554da53bbb..f51159f0d75d5 100644
--- a/mm/frontswap.c
+++ b/mm/frontswap.c
@@ -179,7 +179,7 @@ void frontswap_init(unsigned type, unsigned long *map)
 		ops->init(type);
 }
 
-bool __frontswap_test(struct swap_info_struct *sis,
+static bool __frontswap_test(struct swap_info_struct *sis,
 				pgoff_t offset)
 {
 	if (sis->frontswap_map)
-- 
2.30.2

[PATCH 10/13] frontswap: simplify frontswap_register_ops

[Christoph Hellwig]

Given that frontswap_register_ops must be called from built-in code,
there is no need to handle the case of swapfiles coming online before
or during it, so delete the code that deals with that case.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 mm/frontswap.c | 41 -----------------------------------------
 1 file changed, 41 deletions(-)

diff --git a/mm/frontswap.c b/mm/frontswap.c
index f51159f0d75d5..35040fa4eba83 100644
--- a/mm/frontswap.c
+++ b/mm/frontswap.c
@@ -99,25 +99,6 @@ static inline void inc_frontswap_invalidates(void) { }
  */
 void frontswap_register_ops(struct frontswap_ops *ops)
 {
-	DECLARE_BITMAP(a, MAX_SWAPFILES);
-	DECLARE_BITMAP(b, MAX_SWAPFILES);
-	struct swap_info_struct *si;
-	unsigned int i;
-
-	bitmap_zero(a, MAX_SWAPFILES);
-	bitmap_zero(b, MAX_SWAPFILES);
-
-	spin_lock(&swap_lock);
-	plist_for_each_entry(si, &swap_active_head, list) {
-		if (!WARN_ON(!si->frontswap_map))
-			__set_bit(si->type, a);
-	}
-	spin_unlock(&swap_lock);
-
-	/* the new ops needs to know the currently active swap devices */
-	for_each_set_bit(i, a, MAX_SWAPFILES)
-		ops->init(i);
-
 	/*
 	 * Setting frontswap_ops must happen after the ops->init() calls
 	 * above; cmpxchg implies smp_mb() which will ensure the init is
@@ -128,28 +109,6 @@ void frontswap_register_ops(struct frontswap_ops *ops)
 	} while (cmpxchg(&frontswap_ops, ops->next, ops) != ops->next);
 
 	static_branch_inc(&frontswap_enabled_key);
-
-	spin_lock(&swap_lock);
-	plist_for_each_entry(si, &swap_active_head, list) {
-		if (si->frontswap_map)
-			__set_bit(si->type, b);
-	}
-	spin_unlock(&swap_lock);
-
-	/*
-	 * On the very unlikely chance that a swap device was added or
-	 * removed between setting the "a" list bits and the ops init
-	 * calls, we re-check and do init or invalidate for any changed
-	 * bits.
-	 */
-	if (unlikely(!bitmap_equal(a, b, MAX_SWAPFILES))) {
-		for (i = 0; i < MAX_SWAPFILES; i++) {
-			if (!test_bit(i, a) && test_bit(i, b))
-				ops->init(i);
-			else if (test_bit(i, a) && !test_bit(i, b))
-				ops->invalidate_area(i);
-		}
-	}
 }
 
 /*
-- 
2.30.2

[PATCH 11/13] mm: mark swap_lock and swap_active_head static

[Christoph Hellwig]

swap_lock and swap_active_head are only used in swapfile.c, so mark them
static.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 include/linux/swapfile.h | 2 --
 mm/swapfile.c            | 4 ++--
 2 files changed, 2 insertions(+), 4 deletions(-)

diff --git a/include/linux/swapfile.h b/include/linux/swapfile.h
index 809cd01ef2c57..54078542134c1 100644
--- a/include/linux/swapfile.h
+++ b/include/linux/swapfile.h
@@ -6,8 +6,6 @@
  * these were static in swapfile.c but frontswap.c needs them and we don't
  * want to expose them to the dozens of source files that include swap.h
  */
-extern spinlock_t swap_lock;
-extern struct plist_head swap_active_head;
 extern struct swap_info_struct *swap_info[];
 extern unsigned long generic_max_swapfile_size(void);
 extern unsigned long max_swapfile_size(void);
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 82342c77791bb..bf0df7aa7158f 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -49,7 +49,7 @@ static bool swap_count_continued(struct swap_info_struct *, pgoff_t,
 				 unsigned char);
 static void free_swap_count_continuations(struct swap_info_struct *);
 
-DEFINE_SPINLOCK(swap_lock);
+static DEFINE_SPINLOCK(swap_lock);
 static unsigned int nr_swapfiles;
 atomic_long_t nr_swap_pages;
 /*
@@ -71,7 +71,7 @@ static const char Unused_offset[] = "Unused swap offset entry ";
  * all active swap_info_structs
  * protected with swap_lock, and ordered by priority.
  */
-PLIST_HEAD(swap_active_head);
+static PLIST_HEAD(swap_active_head);
 
 /*
  * all available (active, not full) swap_info_structs
-- 
2.30.2

[PATCH 12/13] frontswap: remove support for multiple ops

[Christoph Hellwig]

There is only a single instance of frontswap ops in the kernel, so
simplify the frontswap code by removing support for multiple operations.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 include/linux/frontswap.h |  3 +--
 mm/frontswap.c            | 50 ++++++++++-----------------------------
 mm/zswap.c                |  8 +++++--
 3 files changed, 19 insertions(+), 42 deletions(-)

diff --git a/include/linux/frontswap.h b/include/linux/frontswap.h
index c5b2848d22404..a631bac12220c 100644
--- a/include/linux/frontswap.h
+++ b/include/linux/frontswap.h
@@ -13,10 +13,9 @@ struct frontswap_ops {
 	int (*load)(unsigned, pgoff_t, struct page *); /* load a page */
 	void (*invalidate_page)(unsigned, pgoff_t); /* page no longer needed */
 	void (*invalidate_area)(unsigned); /* swap type just swapoff'ed */
-	struct frontswap_ops *next; /* private pointer to next ops */
 };
 
-extern void frontswap_register_ops(struct frontswap_ops *ops);
+int frontswap_register_ops(const struct frontswap_ops *ops);
 
 extern void frontswap_init(unsigned type, unsigned long *map);
 extern int __frontswap_store(struct page *page);
diff --git a/mm/frontswap.c b/mm/frontswap.c
index 35040fa4eba83..6f69b044a8cc7 100644
--- a/mm/frontswap.c
+++ b/mm/frontswap.c
@@ -27,10 +27,7 @@ DEFINE_STATIC_KEY_FALSE(frontswap_enabled_key);
  * may be registered, but implementations can never deregister.  This
  * is a simple singly-linked list of all registered implementations.
  */
-static struct frontswap_ops *frontswap_ops __read_mostly;
-
-#define for_each_frontswap_ops(ops)		\
-	for ((ops) = frontswap_ops; (ops); (ops) = (ops)->next)
+static const struct frontswap_ops *frontswap_ops __read_mostly;
 
 #ifdef CONFIG_DEBUG_FS
 /*
@@ -97,18 +94,14 @@ static inline void inc_frontswap_invalidates(void) { }
 /*
  * Register operations for frontswap
  */
-void frontswap_register_ops(struct frontswap_ops *ops)
+int frontswap_register_ops(const struct frontswap_ops *ops)
 {
-	/*
-	 * Setting frontswap_ops must happen after the ops->init() calls
-	 * above; cmpxchg implies smp_mb() which will ensure the init is
-	 * complete at this point.
-	 */
-	do {
-		ops->next = frontswap_ops;
-	} while (cmpxchg(&frontswap_ops, ops->next, ops) != ops->next);
+	if (frontswap_ops)
+		return -EINVAL;
 
+	frontswap_ops = ops;
 	static_branch_inc(&frontswap_enabled_key);
+	return 0;
 }
 
 /*
@@ -117,7 +110,6 @@ void frontswap_register_ops(struct frontswap_ops *ops)
 void frontswap_init(unsigned type, unsigned long *map)
 {
 	struct swap_info_struct *sis = swap_info[type];
-	struct frontswap_ops *ops;
 
 	VM_BUG_ON(sis == NULL);
 
@@ -133,9 +125,7 @@ void frontswap_init(unsigned type, unsigned long *map)
 	 * p->frontswap set to something valid to work properly.
 	 */
 	frontswap_map_set(sis, map);
-
-	for_each_frontswap_ops(ops)
-		ops->init(type);
+	frontswap_ops->init(type);
 }
 
 static bool __frontswap_test(struct swap_info_struct *sis,
@@ -174,7 +164,6 @@ int __frontswap_store(struct page *page)
 	int type = swp_type(entry);
 	struct swap_info_struct *sis = swap_info[type];
 	pgoff_t offset = swp_offset(entry);
-	struct frontswap_ops *ops;
 
 	VM_BUG_ON(!frontswap_ops);
 	VM_BUG_ON(!PageLocked(page));
@@ -188,16 +177,10 @@ int __frontswap_store(struct page *page)
 	 */
 	if (__frontswap_test(sis, offset)) {
 		__frontswap_clear(sis, offset);
-		for_each_frontswap_ops(ops)
-			ops->invalidate_page(type, offset);
+		frontswap_ops->invalidate_page(type, offset);
 	}
 
-	/* Try to store in each implementation, until one succeeds. */
-	for_each_frontswap_ops(ops) {
-		ret = ops->store(type, offset, page);
-		if (!ret) /* successful store */
-			break;
-	}
+	ret = frontswap_ops->store(type, offset, page);
 	if (ret == 0) {
 		__frontswap_set(sis, offset);
 		inc_frontswap_succ_stores();
@@ -220,7 +203,6 @@ int __frontswap_load(struct page *page)
 	int type = swp_type(entry);
 	struct swap_info_struct *sis = swap_info[type];
 	pgoff_t offset = swp_offset(entry);
-	struct frontswap_ops *ops;
 
 	VM_BUG_ON(!frontswap_ops);
 	VM_BUG_ON(!PageLocked(page));
@@ -230,11 +212,7 @@ int __frontswap_load(struct page *page)
 		return -1;
 
 	/* Try loading from each implementation, until one succeeds. */
-	for_each_frontswap_ops(ops) {
-		ret = ops->load(type, offset, page);
-		if (!ret) /* successful load */
-			break;
-	}
+	ret = frontswap_ops->load(type, offset, page);
 	if (ret == 0)
 		inc_frontswap_loads();
 	return ret;
@@ -247,7 +225,6 @@ int __frontswap_load(struct page *page)
 void __frontswap_invalidate_page(unsigned type, pgoff_t offset)
 {
 	struct swap_info_struct *sis = swap_info[type];
-	struct frontswap_ops *ops;
 
 	VM_BUG_ON(!frontswap_ops);
 	VM_BUG_ON(sis == NULL);
@@ -255,8 +232,7 @@ void __frontswap_invalidate_page(unsigned type, pgoff_t offset)
 	if (!__frontswap_test(sis, offset))
 		return;
 
-	for_each_frontswap_ops(ops)
-		ops->invalidate_page(type, offset);
+	frontswap_ops->invalidate_page(type, offset);
 	__frontswap_clear(sis, offset);
 	inc_frontswap_invalidates();
 }
@@ -268,7 +244,6 @@ void __frontswap_invalidate_page(unsigned type, pgoff_t offset)
 void __frontswap_invalidate_area(unsigned type)
 {
 	struct swap_info_struct *sis = swap_info[type];
-	struct frontswap_ops *ops;
 
 	VM_BUG_ON(!frontswap_ops);
 	VM_BUG_ON(sis == NULL);
@@ -276,8 +251,7 @@ void __frontswap_invalidate_area(unsigned type)
 	if (sis->frontswap_map == NULL)
 		return;
 
-	for_each_frontswap_ops(ops)
-		ops->invalidate_area(type);
+	frontswap_ops->invalidate_area(type);
 	atomic_set(&sis->frontswap_pages, 0);
 	bitmap_zero(sis->frontswap_map, sis->max);
 }
diff --git a/mm/zswap.c b/mm/zswap.c
index 7944e3e57e781..cdf6950fcb2e3 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -1378,7 +1378,7 @@ static void zswap_frontswap_init(unsigned type)
 	zswap_trees[type] = tree;
 }
 
-static struct frontswap_ops zswap_frontswap_ops = {
+static const struct frontswap_ops zswap_frontswap_ops = {
 	.store = zswap_frontswap_store,
 	.load = zswap_frontswap_load,
 	.invalidate_page = zswap_frontswap_invalidate_page,
@@ -1475,11 +1475,15 @@ static int __init init_zswap(void)
 	if (!shrink_wq)
 		goto fallback_fail;
 
-	frontswap_register_ops(&zswap_frontswap_ops);
+	ret = frontswap_register_ops(&zswap_frontswap_ops);
+	if (ret)
+		goto destroy_wq;
 	if (zswap_debugfs_init())
 		pr_warn("debugfs initialization failed\n");
 	return 0;
 
+destroy_wq:
+	destroy_workqueue(shrink_wq);
 fallback_fail:
 	if (pool)
 		zswap_pool_destroy(pool);
-- 
2.30.2

[PATCH 13/13] mm: hide the FRONTSWAP Kconfig symbol

[Christoph Hellwig]

Select FRONTSWAP from ZSWAP instead of prompting for it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 mm/Kconfig | 18 +++---------------
 1 file changed, 3 insertions(+), 15 deletions(-)

diff --git a/mm/Kconfig b/mm/Kconfig
index 430240289b02b..3326ee3903f33 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -445,20 +445,7 @@ config HAVE_SETUP_PER_CPU_AREA
 	bool
 
 config FRONTSWAP
-	bool "Enable frontswap to cache swap pages if tmem is present"
-	depends on SWAP
-	help
-	  Frontswap is so named because it can be thought of as the opposite
-	  of a "backing" store for a swap device.  The data is stored into
-	  "transcendent memory", memory that is not directly accessible or
-	  addressable by the kernel and is of unknown and possibly
-	  time-varying size.  When space in transcendent memory is available,
-	  a significant 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
-	  and swap data is stored as normal on the matching swap device.
-
-	  If unsure, say Y to enable frontswap.
+	bool
 
 config CMA
 	bool "Contiguous Memory Allocator"
@@ -523,7 +510,8 @@ config MEM_SOFT_DIRTY
 
 config ZSWAP
 	bool "Compressed cache for swap pages (EXPERIMENTAL)"
-	depends on FRONTSWAP && CRYPTO=y
+	depends on SWAP && CRYPTO=y
+	select FRONTSWAP
 	select ZPOOL
 	help
 	  A lightweight compressed cache for swap pages.  It takes
-- 
2.30.2

Re: [PATCH 01/13] mm: remove cleancache

[Juergen Gross]

[-- Attachment #1.1.1: Type: text/plain, Size: 477 bytes --]

On 24.12.21 07:22, Christoph Hellwig wrote:
> The cleancache subsystem is unused since the removal of Xen tmem driver
> in commit 814bbf49dcd0 ("xen: remove tmem driver").
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Hehe, this is nearly a verbatim copy of the patch I sent in 2019 (I only
missed the defconfig parts back then):

https://lore.kernel.org/lkml/20190527103207.13287-3-jgross@suse.com/

Reviewed-by: Juergen Gross <jgross@suse.com>


Juergen

[-- Attachment #1.1.2: OpenPGP public key --]
[-- Type: application/pgp-keys, Size: 3135 bytes --]

[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 495 bytes --]

Re: [PATCH 01/13] mm: remove cleancache

[Christoph Hellwig]

On Fri, Dec 24, 2021 at 08:01:32AM +0100, Juergen Gross wrote:
> On 24.12.21 07:22, Christoph Hellwig wrote:
>> The cleancache subsystem is unused since the removal of Xen tmem driver
>> in commit 814bbf49dcd0 ("xen: remove tmem driver").
>>
>> Signed-off-by: Christoph Hellwig <hch@lst.de>
>
> Hehe, this is nearly a verbatim copy of the patch I sent in 2019 (I only
> missed the defconfig parts back then):
>
> https://lore.kernel.org/lkml/20190527103207.13287-3-jgross@suse.com/
>
> Reviewed-by: Juergen Gross <jgross@suse.com>

I'm perfectly fine with changing the attribution to your here a well.

Re: [PATCH 01/13] mm: remove cleancache

[Geert Uytterhoeven]

On Sat, Dec 25, 2021 at 2:41 AM Christoph Hellwig <hch@lst.de> wrote:
> The cleancache subsystem is unused since the removal of Xen tmem driver
> in commit 814bbf49dcd0 ("xen: remove tmem driver").
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>

>  arch/m68k/configs/amiga_defconfig    |   1 -
>  arch/m68k/configs/apollo_defconfig   |   1 -
>  arch/m68k/configs/atari_defconfig    |   1 -
>  arch/m68k/configs/bvme6000_defconfig |   1 -
>  arch/m68k/configs/hp300_defconfig    |   1 -
>  arch/m68k/configs/mac_defconfig      |   1 -
>  arch/m68k/configs/multi_defconfig    |   1 -
>  arch/m68k/configs/mvme147_defconfig  |   1 -
>  arch/m68k/configs/mvme16x_defconfig  |   1 -
>  arch/m68k/configs/q40_defconfig      |   1 -
>  arch/m68k/configs/sun3_defconfig     |   1 -
>  arch/m68k/configs/sun3x_defconfig    |   1 -

Although this would be removed during the next refresh anyway:
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>

> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -444,28 +444,6 @@ config USE_PERCPU_NUMA_NODE_ID
>  config HAVE_SETUP_PER_CPU_AREA
>         bool
>
> -config CLEANCACHE
> -       bool "Enable cleancache driver to cache clean pages if tmem is present"
> -       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
> -         cleancache 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

Ah, the joy of good advice...

> -
>  config FRONTSWAP
>         bool "Enable frontswap to cache swap pages if tmem is present"
>         depends on SWAP

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: remove Xen tmem leftovers

[David Hildenbrand]

On 24.12.21 07:22, Christoph Hellwig wrote:
> Hi all,
> 
> since the remove of the Xen tmem driver in 2019, the cleancache hooks are
> entirely unused, as are large parts of frontswap.  This series against
> linux-next (with the folio changes included) removes cleancaches, and cuts
> down frontswap to the bits actually used by zswap.
> 

Just out of curiosity, why was tmem removed from Linux (or even Xen?).
Do you have any information?

Happy to see this cleanup.

-- 
Thanks,

David / dhildenb

Re: remove Xen tmem leftovers

[Christoph Hellwig]

On Tue, Jan 04, 2022 at 03:31:20PM +0100, David Hildenbrand wrote:
> Just out of curiosity, why was tmem removed from Linux (or even Xen?).
> Do you have any information?

"The Xen tmem (transcendent memory) driver can be removed, as the
 related Xen hypervisor feature never made it past the "experimental"
 state and will be removed in future Xen versions (>= 4.13).
	    
 The xen-selfballoon driver depends on tmem, so it can be
 removed, too."

Re: remove Xen tmem leftovers

[Juergen Gross]

[-- Attachment #1.1.1: Type: text/plain, Size: 774 bytes --]

On 04.01.22 15:31, David Hildenbrand wrote:
> On 24.12.21 07:22, Christoph Hellwig wrote:
>> Hi all,
>>
>> since the remove of the Xen tmem driver in 2019, the cleancache hooks are
>> entirely unused, as are large parts of frontswap.  This series against
>> linux-next (with the folio changes included) removes cleancaches, and cuts
>> down frontswap to the bits actually used by zswap.
>>
> 
> Just out of curiosity, why was tmem removed from Linux (or even Xen?).
> Do you have any information?

tmem never made it past the "experimental" state in the Xen hypervisor.
Its implementation had some significant security flaws, there was no
maintainer left, and nobody stepped up to address those issues.

As a result tmem was removed from Xen.


Juergen

[-- Attachment #1.1.2: OpenPGP public key --]
[-- Type: application/pgp-keys, Size: 3135 bytes --]

[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 495 bytes --]

Re: remove Xen tmem leftovers

[David Hildenbrand]

On 05.01.22 07:08, Juergen Gross wrote:
> On 04.01.22 15:31, David Hildenbrand wrote:
>> On 24.12.21 07:22, Christoph Hellwig wrote:
>>> Hi all,
>>>
>>> since the remove of the Xen tmem driver in 2019, the cleancache hooks are
>>> entirely unused, as are large parts of frontswap.  This series against
>>> linux-next (with the folio changes included) removes cleancaches, and cuts
>>> down frontswap to the bits actually used by zswap.
>>>
>>
>> Just out of curiosity, why was tmem removed from Linux (or even Xen?).
>> Do you have any information?
> 
> tmem never made it past the "experimental" state in the Xen hypervisor.
> Its implementation had some significant security flaws, there was no
> maintainer left, and nobody stepped up to address those issues.
> 
> As a result tmem was removed from Xen.

Interesting, thanks for sharing. I know tmem mostly from the papers and
thought it was an interesting approach in general. There was even papers
about a virtio implementation, however, actual code never appeared in
the wild :)

-- 
Thanks,

David / dhildenb

Re: remove Xen tmem leftovers

[Konrad Rzeszutek Wilk]

On Wed, Jan 05, 2022 at 09:46:05AM +0100, David Hildenbrand wrote:
> On 05.01.22 07:08, Juergen Gross wrote:
> > On 04.01.22 15:31, David Hildenbrand wrote:
> >> On 24.12.21 07:22, Christoph Hellwig wrote:
> >>> Hi all,
> >>>
> >>> since the remove of the Xen tmem driver in 2019, the cleancache hooks are
> >>> entirely unused, as are large parts of frontswap.  This series against
> >>> linux-next (with the folio changes included) removes cleancaches, and cuts
> >>> down frontswap to the bits actually used by zswap.
> >>>
> >>
> >> Just out of curiosity, why was tmem removed from Linux (or even Xen?).
> >> Do you have any information?
> > 
> > tmem never made it past the "experimental" state in the Xen hypervisor.
> > Its implementation had some significant security flaws, there was no
> > maintainer left, and nobody stepped up to address those issues.
> > 
> > As a result tmem was removed from Xen.
> 
> Interesting, thanks for sharing. I know tmem mostly from the papers and
> thought it was an interesting approach in general. There was even papers
> about a virtio implementation, however, actual code never appeared in
> the wild :)

There is a repo of it .. I can find it if you are interested - but as
Juergen mentioned - I didn't have enough steam to finish up the security
rework so code removed.