Re: [PATCH v4 0/2] mm/swap: skip empty clusters in the swapoff scan

[Andrew Morton]

On Thu, 10 Sep 2026 01:15:50 +0900 Youngjun Park <youngjun.park@xxxxxxx> wrote:

> find_next_to_unuse() walks a swap device one offset at a time.  Slot
> state now lives in a per cluster swap table, so patch 2 dismisses an
> empty cluster with one counter read instead of SWAPFILE_CLUSTER table
> reads.
> 
> Patch 1 is an unrelated one line comment fix noticed on the way.
> 
> A debug test confirmed the skip path runs, and swapoff completed
> under load with no DEBUG_VM or lockdep splats.

Please let's try to make the [0/N] words provide a summary of the
patchset's effects.  The above didn't even tell people that this is a
swapoff optimization!

I asked an LLM for this summary and we came up with

:  Speed up swapoff and reduce scanning stalls on large, mostly empty
:  swap devices by skipping empty clusters.  Reduce swapoff time on a 1
:  TiB device from 158 ms to 94 ms after filling 128 GiB, and from 392
:  ms to 73 ms after filling 512 GiB; expect little benefit when
:  substantial swap data remains.

Does that sound OK?