Re: [RFC PATCH] mm/damon/reclaim: allow disabling watermarks to force reclaim of cold pages

[SJ Park <sj@kernel.org>]

On Tue, 27 Oct 2026 17:46:11 +0800 Jinjie Ruan <ruanjinjie@huawei.com> wrote:

> 
> 
> 在 2026/10/20 21:58, SJ Park 写道:
> > Hello Jinjie,
> > 
> > On Tue, 20 Oct 2026 21:32:33 +0800 Jinjie Ruan <ruanjinjie@huawei.com> wrote:
> > 
> >> DAMON_RECLAIM runs its scheme only while the free memory rate is in
> >> [wmarks_low, wmarks_mid].  Reclaiming cold pages raises the rate, so the
> >> scheme self-stops as soon as memory looks plentiful again, which is wrong
> >> for a VMM parking an idle sandbox that wants cold anonymous pages
> >> reclaimed immediately.
> >>
> >> So add an ignore_wmarks module parameter. When set, the scheme uses
> >> DAMOS_WMARK_NONE, so damos_wmark_wait_us() always returns zero and the
> >> scheme stays active, bounded only by min_age and the quota.
> > 
> > I agree there could be use cases that doesn't want the watermarks at all.  I'd
> > like to avoid adding new DAMON_RECLAIM parameters if possible, though.  That's
> > becasuse DAMON_RECLAIM is introduced to let people use it without complicated
> > setups.  We will of course add new parameters if really needed, but I want to
> > see if there is a good alternative.
> > 
> > Have you considered some other alternatives?  For example, could respectively
> > setting wmarks_high, wmarks_mid and wmarks_low to 100%, 100% and 0% effectively
> > disable watermarks?  Have you tried that?  If that works, how about updating
> 
> Hi SJ,
> 
> Yes, it does for my use case.

Thank you for confirming.

> 
> > document to clearly explain the usage?  Also, have you considered using DAMON
> 
> Thank you! I will send a patch to update the doc later.

Looking forward to your patch!

> 
> > sysfs interface instead of DAMON_RECLAIM?
> 
> DAMON sysfs can also do this with "none" watermarks. But I want the
> simple DAMON_RECLAIM for only proactive reclam.

Thank you for clarifying, that makes sense to me.


Thanks,
SJ

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