linux-kernel - Re: [PATCH -next] mm: introduce per-node proactive reclaim interface

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Message-ID: <CAJD7tkYe5xJjMw1KtHRyvCLeGKBgZpU1RNzb_Y=c_NujioYXnA@mail.gmail.com>
Date: Thu, 5 Sep 2024 00:31:08 -0700
From: Yosry Ahmed <yosryahmed@...gle.com>
To: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org, mhocko@...nel.org, 
	rientjes@...gle.com, yosryahmed@...gle.com, hannes@...xchg.org, 
	almasrymina@...gle.com, roman.gushchin@...ux.dev, gthelen@...gle.com, 
	dseo3@....edu, a.manzanares@...sung.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next] mm: introduce per-node proactive reclaim interface

On Wed, Sep 4, 2024 at 8:35 PM Davidlohr Bueso <dave@...olabs.net> wrote:
>
> On Wed, 04 Sep 2024, Andrew Morton wrote:\n
> >On Wed, 4 Sep 2024 18:08:05 -0700 Davidlohr Bueso <dave@...olabs.net> wrote:
> >
> >> On Wed, 04 Sep 2024, Andrew Morton wrote:\n
> >> >On Wed,  4 Sep 2024 09:27:40 -0700 Davidlohr Bueso <dave@...olabs.net> wrote:
> >> >
> >> >> This adds support for allowing proactive reclaim in general on a
> >> >> NUMA system. A per-node interface extends support for beyond a
> >> >> memcg-specific interface, respecting the current semantics of
> >> >> memory.reclaim: respecting aging LRU and not supporting
> >> >> artificially triggering eviction on nodes belonging to non-bottom
> >> >> tiers.
> >> >>
> >> >> This patch allows userspace to do:
> >> >>
> >> >>      echo 512M swappiness=10 > /sys/devices/system/node/nodeX/reclaim
> >> >
> >> >One value per sysfs file is a rule.
> >>
> >> I wasn't aware of it as a rule - is this documented somewhere?
> >
> >Documentation/filesystems/sysfs.rst, line 62.  Also lots of gregkh
> >grumpygrams :)
> >
> >> I ask because I see some others are using space-separated parameters, ie:
> >>
> >> /sys/bus/usb/drivers/foo/new_id
> >>
> >> ... or colons. What would be acceptable? echo "512M:10" > ... ?
> >
> >Kinda cheating.  But the rule gets violated a lot.
>
> The only other alternative I can think of is to have a separate file
> for swappiness, which of course sucks. So I will go with the colon
> approach unless somebody shouts - I still prefer it as is in this patch,
> if we are going to violate the rule altogether...

I also prefer this patch's approach. It'd be really confusing if the
per-node and per-memcg proactive reclaim interfaces have the same
semantics but different syntax.