linux-kernel - Re: [RFC PATCH 01/11] mm/mempolicy: implement the sysfs-based weighted

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Date:   Thu, 7 Dec 2023 19:11:59 -0500
From:   Gregory Price <gregory.price@...verge.com>
To:     Gregory Price <gourry.memverge@...il.com>, linux-mm@...ck.org,
        jgroves@...ron.com, ravis.opensrc@...ron.com,
        sthanneeru@...ron.com, emirakhur@...ron.com, Hasan.Maruf@....com,
        linux-doc@...r.kernel.org, linux-fsdevel@...r.kernel.org,
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        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
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        peterz@...radead.org
Subject: Re: [RFC PATCH 01/11] mm/mempolicy: implement the sysfs-based
 weighted_interleave interface

On Thu, Dec 07, 2023 at 01:56:07PM -0800, Davidlohr Bueso wrote:
> On Wed, 06 Dec 2023, Gregory Price wrote:
> > +
> > +What:		/sys/kernel/mm/mempolicy/weighted_interleave/nodeN/
> > +Date:		December 2023
> > +Contact:	Linux memory management mailing list <linux-mm@...ck.org>
> > +Description:	Configuration interface for accesses initiated from nodeN
> > +
> > +		The directory to configure access initiator weights for nodeN.
> > +
> > +		Possible numa nodes which have not been marked as a CPU node
> > +		at boot will not have a nodeN directory made for them at boot.
> 
> This could be better rephrased without the negation. ie:
> 
> "Only numa nodes with CPUs (compute) will have a nodeN directory."
> 

I thought documentation was supposed to be as confusing as possible.

lol I'll update it.  reading it now, this is awful.

> > +		Hotplug for CPU nodes is not supported.
> 
> Can this even happen? Hot-adding a previously offlined CPU won't change/add a
> new numa node. So just rm the line altogether?
>

I... have no idea.  In that sense, aye aye!

> > +static ssize_t node_weight_show(struct kobject *kobj,
> > +				struct kobj_attribute *attr, char *buf)
> > +
> > +static ssize_t node_weight_store(struct kobject *kobj,
> > +				 struct kobj_attribute *attr,
> > +				 const char *buf, size_t count)
> 
> iw_table will need some (basic) form of serialization.
> 

originally the SKH group recommended a serialized "N*W,N*W,..." format,
but this doesn't work for a matrix.

Possibly i could add `N-M*W,...;N-M*W,...` and add a nodeN/weightlist
interface that lets you acquire the whole iw_table for one or more
nodes.  Might be a nice extension.

I figured there is an aversion to multi-value sysfs files, so I reverted
back to a one-file-one-value file.  If there is a preference for the
fully serialized methods, I'll happily add those.  Easy enough and I
already have the code to parse it.

~Gregory