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

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Message-ID: <a2fdrnaagcgp4hllalttaxs7ckc6w5bt2j7fg4upagqhfvoc3b@jsmugftxvyyz>
Date: Wed, 4 Sep 2024 20:35:22 -0700
From: Davidlohr Bueso <dave@...olabs.net>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: 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, 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...