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52f37efc59
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Baoquan He 52f37efc59 mm/swap: select swap device with default priority round robin 
Swap devices are assumed to have similar accessing speed when swapon if no
priority is specified.  It's unfair and doesn't make sense just because
one swap device is swapped on firstly, its priority will be higher than
the one swapped on later.

Here, set all swap devicess to have priority '-1' by default.  With this
change, swap device with default priority will be selected round robin
when swapping out.  This can improve the swapping efficiency a lot among
multiple swap devices with default priority.

Below are swapon output during the processes when high pressure
vm-scability test is being taken:

1) This is pre-commit a2468cc9bf, swap device is selectd one by one by
   priority from high to low when one swap device is exhausted:
------------------------------------
[root@hp-dl385g10-03 ~]# swapon
NAME       TYPE      SIZE   USED PRIO
/dev/zram0 partition  16G    16G   -1
/dev/zram1 partition  16G 966.2M   -2
/dev/zram2 partition  16G     0B   -3
/dev/zram3 partition  16G     0B   -4

2) This is behaviour with commit a2468cc9bf, on node, swap device
   sharing the same node id is selected firstly until exhausted; while
   on node no swap device sharing the node id it selects the one with
   highest priority until exhaustd:
------------------------------------
[root@hp-dl385g10-03 ~]# swapon
NAME       TYPE      SIZE  USED PRIO
/dev/zram0 partition  16G 15.7G   -2
/dev/zram1 partition  16G  3.4G   -3
/dev/zram2 partition  16G  3.4G   -4
/dev/zram3 partition  16G  2.6G   -5

3) After this patch applied, swap devices with default priority are selectd
   round robin:
------------------------------------
[root@hp-dl385g10-03 block]# swapon
NAME       TYPE      SIZE USED PRIO
/dev/zram0 partition  16G 6.6G   -1
/dev/zram1 partition  16G 6.6G   -1
/dev/zram2 partition  16G 6.6G   -1
/dev/zram3 partition  16G 6.6G   -1

With the change, about 18% efficiency promotion relative to node based
way as below. (Surely, the pre-commit a2468cc9bf way is the worst.)

vm-scability test:
==================
Test with:
usemem --init-time -O -y -x -n 31 2G (4G memcg, zram as swap)
                            one by one:      node based:      round robin:
System time:                1087.38 s        637.92 s         526.74 s     (lower is better)
Sum Throughput:             2036.55 MB/s     3546.56 MB/s     4207.56 MB/s (higher is better)
Single process Throughput:  65.69 MB/s       114.40 MB/s      135.72 MB/s  (high is better)
free latency:               15769409.48 us   10138455.99 us   6810119.01 us(lower is better)

Link: https://lkml.kernel.org/r/20251028034308.929550-3-bhe@redhat.com
Signed-off-by: Baoquan He <bhe@redhat.com>
Suggested-by: Chris Li <chrisl@kernel.org>
Acked-by: Chris Li <chrisl@kernel.org>
Acked-by: Nhat Pham <nphamcs@gmail.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2025-11-16 17:28:27 -08:00
arch mm: make INVALID_PHYS_ADDR a generic macro 2025-11-16 17:28:26 -08:00
block block-6.18-20251031 2025-10-31 12:57:19 -07:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto This push contains the following changes: 2025-10-10 08:56:16 -07:00
Documentation mm/swap: do not choose swap device according to numa node 2025-11-16 17:28:27 -08:00
drivers mm: make INVALID_PHYS_ADDR a generic macro 2025-11-16 17:28:26 -08:00
fs treewide: include linux/pgalloc.h instead of asm/pgalloc.h 2025-11-16 17:28:25 -08:00
include mm/swap: do not choose swap device according to numa node 2025-11-16 17:28:27 -08:00
init printk changes for 6.18 2025-10-04 11:13:11 -07:00
io_uring mm: consistently use current->mm in mm_get_unmapped_area() 2025-11-16 17:27:57 -08:00
ipc namespace-6.18-rc1 2025-09-29 11:20:29 -07:00
kernel mm: make INVALID_PHYS_ADDR a generic macro 2025-11-16 17:28:26 -08:00
lib lib/test_vmalloc: remove xfail condition check 2025-11-16 17:27:53 -08:00
LICENSES LICENSES: Replace the obsolete address of the FSF in the GFDL-1.2 2025-07-24 11:15:39 +02:00
mm mm/swap: select swap device with default priority round robin 2025-11-16 17:28:27 -08:00
net Including fixes from bluetooth and wireless. 2025-11-06 08:52:30 -08:00
rust rust: kbuild: workaround rustdoc doctests modifier bug 2025-11-04 00:00:06 +01:00
samples Char/Misc/IIO/Binder changes for 6.18-rc1 2025-10-04 16:26:32 -07:00
scripts scripts/decode_stacktrace.sh: fix build ID and PC source parsing 2025-11-09 21:19:45 -08:00
security integrity-v6.18 2025-10-05 10:48:33 -07:00
sound ASoC: Fixes for v6.18 2025-10-30 13:08:08 +01:00
tools selftests/damon/sysfs: add obsolete_target test 2025-11-16 17:28:25 -08:00
usr gen_init_cpio: Ignore fsync() returning EINVAL on pipes 2025-10-07 09:53:05 -07:00
virt KVM x86 fixes for 6.18: 2025-10-18 10:25:43 +02:00
.clang-format memblock: drop for_each_free_mem_pfn_range_in_zone_from() 2025-09-14 08:49:03 +03:00
.clippy.toml rust: clean Rust 1.88.0's warning about clippy::disallowed_macros configuration 2025-05-07 00:11:47 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore MAINTAINERS: remove Alyssa Rosenzweig 2025-09-18 21:17:31 +02:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore .gitignore: ignore compile_commands.json globally 2025-08-12 15:53:55 -07:00
.mailmap MAINTAINERS: update David Hildenbrand's email address 2025-11-15 10:52:01 -08:00
.pylintrc tools: docs: parse-headers.py: move it from sphinx dir 2025-08-29 15:54:42 -06:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: mark ISDN subsystem as orphan 2025-10-27 17:49:45 -07:00
Kbuild sched: Make migrate_{en,dis}able() inline 2025-09-25 09:57:16 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS MAINTAINERS: add include/linux/pgalloc.h to MM CORE section 2025-11-16 17:28:25 -08:00
Makefile Linux 6.18-rc5 2025-11-09 15:10:19 -08:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.