linux-stable.git/mm/zpool.c, branch master

mm: remove unused zpool layer

2025-09-21T21:21:59+00:00

With zswap using zsmalloc directly, there are no more in-tree users of
this code.  Remove it.

With zpool gone, zsmalloc is now always a simple dependency and no
longer something the user needs to configure. Hide CONFIG_ZSMALLOC
from the user and have zswap and zram pull it in as needed.

Link: https://lkml.kernel.org/r/20250829162212.208258-3-hannes@cmpxchg.org
Signed-off-by: Johannes Weiner 
Acked-by: SeongJae Park 
Acked-by: Yosry Ahmed  
Cc: Chengming Zhou 
Cc: Nhat Pham 
Cc: Vitaly Wool 
Signed-off-by: Andrew Morton

zsmalloc: prefer the the original page's node for compressed data

2025-05-12T00:48:06+00:00

Currently, zsmalloc, zswap's and zram's backend memory allocator, does not
enforce any policy for the allocation of memory for the compressed data,
instead just adopting the memory policy of the task entering reclaim, or
the default policy (prefer local node) if no such policy is specified. 
This can lead to several pathological behaviors in multi-node NUMA
systems:

1. Systems with CXL-based memory tiering can encounter the following
   inversion with zswap/zram: the coldest pages demoted to the CXL tier
   can return to the high tier when they are reclaimed to compressed swap,
   creating memory pressure on the high tier.

2. Consider a direct reclaimer scanning nodes in order of allocation
   preference.  If it ventures into remote nodes, the memory it compresses
   there should stay there.  Trying to shift those contents over to the
   reclaiming thread's preferred node further *increases* its local
   pressure, and provoking more spills.  The remote node is also the most
   likely to refault this data again.  This undesirable behavior was
   pointed out by Johannes Weiner in [1].

3. For zswap writeback, the zswap entries are organized in
   node-specific LRUs, based on the node placement of the original pages,
   allowing for targeted zswap writeback for specific nodes.

   However, the compressed data of a zswap entry can be placed on a
   different node from the LRU it is placed on.  This means that reclaim
   targeted at one node might not free up memory used for zswap entries in
   that node, but instead reclaiming memory in a different node.

All of these issues will be resolved if the compressed data go to the same
node as the original page.  This patch encourages this behavior by having
zswap and zram pass the node of the original page to zsmalloc, and have
zsmalloc prefer the specified node if we need to allocate new (zs)pages
for the compressed data.

Note that we are not strictly binding the allocation to the preferred
node.  We still allow the allocation to fall back to other nodes when the
preferred node is full, or if we have zspages with slots available on a
different node.  This is OK, and still a strict improvement over the
status quo:

1. On a system with demotion enabled, we will generally prefer
   demotions over compressed swapping, and only swap when pages have
   already gone to the lowest tier.  This patch should achieve the desired
   effect for the most part.

2. If the preferred node is out of memory, letting the compressed data
   going to other nodes can be better than the alternative (OOMs, keeping
   cold memory unreclaimed, disk swapping, etc.).

3. If the allocation go to a separate node because we have a zspage
   with slots available, at least we're not creating extra immediate
   memory pressure (since the space is already allocated).

3. While there can be mixings, we generally reclaim pages in same-node
   batches, which encourage zspage grouping that is more likely to go to
   the right node.

4. A strict binding would require partitioning zsmalloc by node, which
   is more complicated, and more prone to regression, since it reduces the
   storage density of zsmalloc.  We need to evaluate the tradeoff and
   benchmark carefully before adopting such an involved solution.

[1]: https://lore.kernel.org/linux-mm/20250331165306.GC2110528@cmpxchg.org/

[senozhatsky@chromium.org: coding-style fixes]
  Link: https://lkml.kernel.org/r/mnvexa7kseswglcqbhlot4zg3b3la2ypv2rimdl5mh5glbmhvz@wi6bgqn47hge
Link: https://lkml.kernel.org/r/20250402204416.3435994-1-nphamcs@gmail.com
Signed-off-by: Nhat Pham 
Suggested-by: Gregory Price 
Acked-by: Dan Williams 
Reviewed-by: Chengming Zhou 
Acked-by: Sergey Senozhatsky 	[zram, zsmalloc]
Acked-by: Johannes Weiner 
Acked-by: Yosry Ahmed 	[zswap/zsmalloc]
Cc: "Huang, Ying" 
Cc: Joanthan Cameron 
Cc: Minchan Kim 
Cc: SeongJae Park 
Signed-off-by: Andrew Morton

mm: zpool: remove zpool_malloc_support_movable()

2025-03-17T07:05:41+00:00

zpool_malloc_support_movable() always returns true for zsmalloc, the only
remaining zpool driver.  Remove it and set the gfp flags in
zswap_compress() accordingly.  Opportunistically use GFP_NOWAIT instead of
__GFP_NOWARN | __GFP_KSWAPD_RECLAIM for conciseness as they are
equivalent.

Link: https://lkml.kernel.org/r/20250305061134.4105762-6-yosry.ahmed@linux.dev
Signed-off-by: Yosry Ahmed 
Reviewed-by: Sergey Senozhatsky 
Acked-by: Johannes Weiner 
Acked-by: Nhat Pham 
Cc: Thomas Gleixner 
Cc: Chengming Zhou 
Cc: Herbert Xu 
Cc: Minchan Kim 
Cc: Peter Zijlstra 
Signed-off-by: Andrew Morton

mm: zpool: remove object mapping APIs

2025-03-17T07:05:40+00:00

zpool_map_handle(), zpool_unmap_handle(), and zpool_can_sleep_mapped() are
no longer used.  Remove them with the underlying driver callbacks.

Link: https://lkml.kernel.org/r/20250305061134.4105762-4-yosry.ahmed@linux.dev
Signed-off-by: Yosry Ahmed 
Reviewed-by: Sergey Senozhatsky 
Acked-by: Johannes Weiner 
Acked-by: Nhat Pham 
Cc: Chengming Zhou 
Cc: Herbert Xu 
Cc: Minchan Kim 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Signed-off-by: Andrew Morton

mm: zpool: add interfaces for object read/write APIs

2025-03-17T07:05:40+00:00

Patch series "Switch zswap to object read/write APIs".

This patch series updates zswap to use the new object read/write APIs
defined by zsmalloc in [1], and remove the old object mapping APIs and the
related code from zpool and zsmalloc.


This patch (of 5):

Zsmalloc introduced new APIs to read/write objects besides mapping them. 
Add the necessary zpool interfaces.

Link: https://lkml.kernel.org/r/20250305061134.4105762-1-yosry.ahmed@linux.dev
Link: https://lkml.kernel.org/r/20250305061134.4105762-2-yosry.ahmed@linux.dev
Signed-off-by: Yosry Ahmed 
Reviewed-by: Sergey Senozhatsky 
Acked-by: Johannes Weiner 
Acked-by: Nhat Pham 
Cc: Chengming Zhou 
Cc: Herbert Xu 
Cc: Minchan Kim 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Signed-off-by: Andrew Morton

mm: zbud: remove zbud

2025-03-17T05:06:01+00:00

The zbud compressed pages allocator is rarely used, most users use
zsmalloc.  zbud consumes much more memory (only stores 1 or 2 compressed
pages per physical page).  The only advantage of zbud is a marginal
performance improvement that by no means justify the memory overhead.

Historically, zsmalloc had significantly worse latency than zbud and
z3fold but offered better memory savings.  This is no longer the case as
shown by a simple recent analysis [1].  In a kernel build test on tmpfs in
a limited cgroup, zbud 2-3% less time than zsmalloc, but at the cost of
using ~32% more memory (1.5G vs 1.13G).  The tradeoff does not make sense
for zbud in any practical scenario.

The only alleged advantage of zbud is not having the dependency on
CONFIG_MMU, but CONFIG_SWAP already depends on CONFIG_MMU anyway, and zbud
is only used by zswap.

Remove zbud after z3fold's removal, leaving zsmalloc as the one and only
zpool allocator.  Leave the removal of the zpool API (and its associated
config options) to a followup cleanup after no more allocators show up.

Deprecating zbud for a few cycles before removing it was initially
proposed [2], like z3fold was marked as deprecated for 2 cycles [3]. 
However, Johannes rightfully pointed out that the 2 cycles is too short
for most downstream consumers, and z3fold was deprecated first only as a
courtesy anyway.

[1]https://lore.kernel.org/lkml/CAJD7tkbRF6od-2x_L8-A1QL3=2Ww13sCj4S3i4bNndqF+3+_Vg@mail.gmail.com/
[2]https://lore.kernel.org/lkml/Z5gdnSX5Lv-nfjQL@google.com/
[3]https://lore.kernel.org/lkml/20240904233343.933462-1-yosryahmed@google.com/

Link: https://lkml.kernel.org/r/20250129180633.3501650-3-yosry.ahmed@linux.dev
Signed-off-by: Yosry Ahmed 
Reviewed-by: Shakeel Butt 
Acked-by: Johannes Weiner 
Acked-by: Nhat Pham 
Cc: Alexander Gordeev 
Cc: Chengming Zhou 
Cc: Christian Borntraeger 
Cc: Dan Streetman 
Cc: Heiko Carstens 
Cc: Huacai Chen 
Cc: Miaohe Lin 
Cc: Seth Jennings 
Cc: Sven Schnelle 
Cc: Vasily Gorbik 
Cc: Vitaly Wool 
Cc: Vlastimil Babka 
Cc: WANG Xuerui 
Signed-off-by: Andrew Morton

mm: zpool: return pool size in pages

2024-04-26T03:55:48+00:00

All zswap backends track their pool sizes in pages.  Currently they
multiply by PAGE_SIZE for zswap, only for zswap to divide again in order
to do limit math.  Report pages directly.

Link: https://lkml.kernel.org/r/20240312153901.3441-2-hannes@cmpxchg.org
Signed-off-by: Johannes Weiner 
Acked-by: Yosry Ahmed 
Reviewed-by: Chengming Zhou 
Reviewed-by: Nhat Pham 
Cc: Yosry Ahmed 
Signed-off-by: Andrew Morton

mm: zswap: remove shrink from zpool interface

2023-06-19T23:19:27+00:00

Now that all three zswap backends have removed their shrink code, it is
no longer necessary for the zpool interface to include shrink/writeback
endpoints.

Link: https://lkml.kernel.org/r/20230612093815.133504-6-cerasuolodomenico@gmail.com
Signed-off-by: Domenico Cerasuolo 
Reviewed-by: Yosry Ahmed 
Acked-by: Nhat Pham 
Acked-by: Johannes Weiner 
Reviewed-by: Sergey Senozhatsky 
Cc: Dan Streetman 
Cc: Minchan Kim 
Cc: Seth Jennings 
Cc: Vitaly Wool 
Signed-off-by: Andrew Morton

zpool: remove MODULE_LICENSE in non-modules

2023-04-13T20:13:54+00:00

Since commit 8b41fc4454e ("kbuild: create modules.builtin without
Makefile.modbuiltin or tristate.conf"), MODULE_LICENSE declarations
are used to identify modules. As a consequence, uses of the macro
in non-modules will cause modprobe to misidentify their containing
object file as a module when it is not (false positives), and modprobe
might succeed rather than failing with a suitable error message.

So remove it in the files in this commit, none of which can be built as
modules.

Signed-off-by: Nick Alcock 
Suggested-by: Luis Chamberlain 
Cc: Luis Chamberlain 
Cc: linux-modules@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: Hitomi Hasegawa 
Cc: Dan Streetman 
Cc: Andrew Morton 
Cc: linux-mm@kvack.org
Signed-off-by: Luis Chamberlain

zpool: clean out dead code

2022-12-12T02:12:10+00:00

There is a lot of provision for flexibility that isn't actually needed or
used.  Zswap (the only zpool user) always passes zpool_ops with an .evict
method set.  The backends who reclaim only do so for zswap, so they can
also directly call zpool_ops without indirection or checks.

Finally, there is no need to check the retries parameters and bail with
-EINVAL in the reclaim function, when that's called just a few lines below
with a hard-coded 8.  There is no need to duplicate the evictable and
sleep_mapped attrs from the driver in zpool_ops.

Link: https://lkml.kernel.org/r/20221128191616.1261026-3-nphamcs@gmail.com
Reviewed-by: Sergey Senozhatsky 
Signed-off-by: Johannes Weiner 
Signed-off-by: Nhat Pham 
Cc: Dan Streetman 
Cc: Minchan Kim 
Cc: Nitin Gupta 
Cc: Seth Jennings 
Cc: Vitaly Wool 
Signed-off-by: Andrew Morton