Re: [PATCH mm-next] mm/swap: free swap cache folios the zap path gave up on

[Nhat Pham]

On Wed, Oct 14, 2026 at 2:08 AM Jiayuan Chen <jiayuan.chen@xxxxxxxxx> wrote:
>
> From: Jiayuan Chen <jiayuan.chen@xxxxxxxxxx>
>
> On our production hosts we saw swap cache only pages keep growing for days:
> on a box with a 500 GiB swap partition, 250 GiB of RAM and 250 GiB of
> swap slots were held by folios that no process mapped any more, charged

That's a really nasty situation.

> to cgroups whose workloads had long exited. The only way to get them
> back was swapoff, and with other services actively swapping on the
> same host that is not an option.

Is it not similar to cold file caches?

The recommendation for these kind of scenarios (for both file and
anon) is to adopt a proactive reclaimer (in the same vein as senpai).
That's what we do internally.

>
> Cc: Jiayuan Chen <jiayuan.chen@xxxxxxxxx>
> Signed-off-by: Jiayuan Chen <jiayuan.chen@xxxxxxxxxx>

Code looks solid to me otherwise. Maybe include some numbers from your
testing in the cover letter to verify that the swap cache usage drop.