Re: [PATCH v5 00/19] mm, swap: extendable swap devices (xswap phase I)

[Baoquan He <baoquan.he@linux.dev>]

On 11/09/26 at 01:54pm, Baoquan He wrote:

Forgot adding change history versions before v4, please refer to below
v4 patchset cover letter if you want to check.

[PATCH v4 00/14] mm, swap: extendable swap devices (xswap phase I)
https://lore.kernel.org/all/20261003003136.750633-1-hebaoquan@kylinos.cn/T/#u

> Changelog
> =========
> v4 -> v5:
> - Rebased onto the latest mm-new (2c5dafa7f289). 
> 
> - A device now has a stable id instead of exposing the swap type:
>   /proc/swaps shows xswap<id>, the debugfs file is named by the id and
>   prints the type as well, and destroy takes the id. The id is assigned
>   per boot and never reused, so a value read earlier cannot name a
>   different device.
> 
> - swapoff accepts the name: swapoff xswap<id> and swapoff -a tear the
>   device down, while a real file or directory keeps precedence. A name
>   that does not exist reports -ENOENT; the sysfs destroy keeps -ENODEV
>   for an id it does not know. The interfaces are now documented in
>   Documentation/ABI/testing/sysfs-kernel-mm-xswap and zswap.rst.
> 
> - CONFIG_XSWAP_DEFAULT_MAX sets the default size of a new device. It
>   takes a percentage of RAM, a size, or "max", and defaults to "200%";
>   xswap.max= still overrides it.
> 
> - The cluster_info accesses are RCU-safe: the allocation fast path bounds
>   a cached cluster against the mapped range, and the shrink drains the
>   per-cpu cache and waits an RCU grace period before unmapping.
> 
> - xswap_grow() now links the clusters it mapped even when swapoff has
>   already cleared SWP_WRITEOK, so a failed swapoff cannot leave them
>   mapped and on no list.
> 
> - swap_info_remove() skips the commit limit probe for xswap; real swap
>   devices keep it. See the overcommit note above.
> 
> - The cgroup zswap gate is checked again after the allocation when an
>   xswap device appeared after the initial lookup, so a slot is not kept
>   for a cgroup that cannot zswap.
> 
> - The patches are reorganized: the VM_SPARSE work is split into helpers
>   and the xswap use, the max/pages widening moves before the sysfs
>   interface, the shrink trigger now carries the workqueue deferral, and
>   the unmap helper is prepared for range shrinking in its own patch. The
>   series is now phase I of four, with the swap-table backend records as
>   a phase of their own.
> 
> Baoquan He (18):
>   mm, swap: refactor free_swap_cluster_info to take swap_info_struct
>   mm, swap: add VM_SPARSE cluster-array helpers for xswap
>   mm, swap: use a VM_SPARSE cluster array for xswap devices
>   mm, swap: widen swap_info_struct max/pages to unsigned long
>   mm, swap: add a sysfs interface to create xswap devices
>   mm, swap: refactor swapoff and add xswap_destroy
>   mm, swap: require zswap for xswap devices
>   mm, swap: use a stable id for xswap devices
>   mm, swap: let the command line set the xswap device size
>   mm, swap: add CONFIG_XSWAP_DEFAULT_MAX
>   mm, swap: let swapoff destroy xswap devices by name
>   mm, swap: add xswap grow trigger on cluster allocation
>   mm, swap: add debugfs counters for xswap
>   mm, swap: make xswap cluster_info accesses RCU-safe
>   mm, swap: prepare xswap_unmap_clusters for range shrinking
>   mm, swap: add xswap shrink trigger and defer it to a workqueue
>   mm, swap: do not give an xswap slot to a cgroup that cannot zswap
>   mm, swap: skip the overcommit probe when removing xswap
> 
> Chris Li (1):
>   mm: xswap support for zswap
> 
>  .../ABI/testing/sysfs-kernel-mm-xswap         |   43 +
>  .../admin-guide/kernel-parameters.txt         |    8 +
>  Documentation/admin-guide/mm/zswap.rst        |    9 +
>  MAINTAINERS                                   |    1 +
>  include/linux/swap.h                          |   17 +-
>  mm/Kconfig                                    |   20 +
>  mm/page_io.c                                  |   19 +
>  mm/swap_state.c                               |    9 +
>  mm/swapfile.c                                 | 1569 +++++++++++++++--
>  mm/zswap.c                                    |   11 +-
>  10 files changed, 1593 insertions(+), 113 deletions(-)
>  create mode 100644 Documentation/ABI/testing/sysfs-kernel-mm-xswap
> 
> 
> base-commit: 2c5dafa7f289d760f4492260b0988029aab478b0
> -- 
> 2.54.0
> 
>