linux.git/mm/zbud.c, branch master

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

mm: zswap: remove page reclaim logic from zbud

2023-06-19T23:19:26+00:00

Switch zbud to the new generic zswap LRU and remove its custom
implementation.

Link: https://lkml.kernel.org/r/20230612093815.133504-3-cerasuolodomenico@gmail.com
Signed-off-by: Domenico Cerasuolo 
Acked-by: Johannes Weiner 
Cc: Dan Streetman 
Cc: Minchan Kim 
Cc: Nhat Pham 
Cc: Sergey Senozhatsky 
Cc: Seth Jennings 
Cc: Vitaly Wool 
Cc: Yosry Ahmed 
Signed-off-by: Andrew Morton

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

mm/zbud: add kerneldoc fields for zbud_pool

2021-07-01T18:06:03+00:00

make W=1 generates the following warning for zbud_pool

  mm/zbud.c:105: warning: Function parameter or member 'zpool' not described in 'zbud_pool'
  mm/zbud.c:105: warning: Function parameter or member 'zpool_ops' not described in 'zbud_pool'

Commit 479305fd7172 ("zpool: remove zpool_evict()") removed the
zpool_evict helper and added the associated zpool and operations structure
in struct zbud_pool but did not add documentation for the fields.  Add
rudimentary documentation.

Link: https://lkml.kernel.org/r/20210520084809.8576-10-mgorman@techsingularity.net
Fixes: 479305fd7172 ("zpool: remove zpool_evict()")
Signed-off-by: Mel Gorman 
Reviewed-by: Yang Shi 
Acked-by: Vlastimil Babka 
Cc: Dan Streetman 
Cc: David Hildenbrand 
Cc: Michal Hocko 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm/zbud: don't export any zbud API

2021-07-01T03:47:29+00:00

The zbud doesn't need to export any API and it is meant to be used via
zpool API since the commit 12d79d64bfd3 ("mm/zpool: update zswap to use
zpool").  So we can remove the unneeded zbud.h and move down zpool API to
avoid any forward declaration.

[linmiaohe@huawei.com: fix unused function warnings when CONFIG_ZPOOL is disabled]
  Link: https://lkml.kernel.org/r/20210619025508.1239386-1-linmiaohe@huawei.com

Link: https://lkml.kernel.org/r/20210608114515.206992-3-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin 
Cc: Dan Streetman 
Cc: Seth Jennings 
Cc: Nathan Chancellor 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm/zbud: reuse unbuddied[0] as buddied in zbud_pool

2021-07-01T03:47:29+00:00

Patch series "Cleanups for zbud", v2.

This series contains just cleanups to save some possible memory in
zbud_pool and avoid exporting any unneeded zbud API.  More details can be
found in the respective changelogs

This patch (of 2):

Since commit 9d8c5b5284e4 ("mm: zbud: fix condition check on allocation
size"), zbud_pool.unbuddied[0] is always unused.  We can reuse it as
buddied field to save some possible memory.

Link: https://lkml.kernel.org/r/20210608114515.206992-1-linmiaohe@huawei.com
Link: https://lkml.kernel.org/r/20210608114515.206992-2-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin 
Cc: Seth Jennings 
Cc: Dan Streetman 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: set the sleep_mapped to true for zbud and z3fold

2021-02-26T17:41:01+00:00

zpool driver adds a flag to indicate whether the zpool driver can enter an
atomic context after mapping.  This patch sets it true for z3fold and
zbud.

Link: https://lkml.kernel.org/r/1611035683-12732-3-git-send-email-tiantao6@hisilicon.com
Signed-off-by: Tian Tao 
Reviewed-by: Vitaly Wool 
Acked-by: Sebastian Andrzej Siewior 
Reported-by: Mike Galbraith 
Cc: Seth Jennings 
Cc: Dan Streetman 
Cc: Barry Song 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm/zbud: remove redundant initialization

2020-10-14T01:38:34+00:00

zhdr is already initialized in the front of the function, so remove
redundant initialization here.

Signed-off-by: Xiang Chen 
Signed-off-by: Andrew Morton 
Reviewed-by: David Hildenbrand 
Cc: Seth Jennings 
Cc: Dan Streetman 
Link: https://lkml.kernel.org/r/1600419885-191907-1-git-send-email-chenxiang66@hisilicon.com
Signed-off-by: Linus Torvalds