linux-kernel - Re: [PATCH v4 11/11] mm/mempolicy: extend set_mempolicy2 and mbind2 to support weighted interleave

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Date: Tue, 19 Dec 2023 13:12:56 -0500
From: Gregory Price <gregory.price@...verge.com>
To: "Huang, Ying" <ying.huang@...el.com>
Cc: Gregory Price <gourry.memverge@...il.com>, linux-mm@...ck.org,
	linux-doc@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
	x86@...nel.org, akpm@...ux-foundation.org, arnd@...db.de,
	tglx@...utronix.de, luto@...nel.org, mingo@...hat.com, bp@...en8.de,
	dave.hansen@...ux.intel.com, hpa@...or.com, mhocko@...nel.org,
	tj@...nel.org, corbet@....net, rakie.kim@...com,
	hyeongtak.ji@...com, honggyu.kim@...com, vtavarespetr@...ron.com,
	peterz@...radead.org, jgroves@...ron.com, ravis.opensrc@...ron.com,
	sthanneeru@...ron.com, emirakhur@...ron.com, Hasan.Maruf@....com,
	seungjun.ha@...sung.com
Subject: Re: [PATCH v4 11/11] mm/mempolicy: extend set_mempolicy2 and mbind2
 to support weighted interleave

On Tue, Dec 19, 2023 at 11:07:10AM +0800, Huang, Ying wrote:
> Gregory Price <gourry.memverge@...il.com> writes:
> 
> > diff --git a/include/uapi/linux/mempolicy.h b/include/uapi/linux/mempolicy.h
> > index ec1402dae35b..16fedf966166 100644
> > --- a/include/uapi/linux/mempolicy.h
> > +++ b/include/uapi/linux/mempolicy.h
> > @@ -33,6 +33,7 @@ struct mpol_args {
> >  	__u16 mode_flags;
> >  	__s32 home_node;	/* mbind2: policy home node */
> >  	__aligned_u64 pol_nodes;
> > +	__aligned_u64 il_weights; /* size: pol_maxnodes * sizeof(char) */
> >  	__u64 pol_maxnodes;
> >  	__s32 policy_node;	/* get_mempolicy: policy node info */
> >  };
> 
> You break the ABI you introduced earlier in the patchset.  Although they
> are done within a patchset, I don't think that it's a good idea.  I
> suggest to finalize the ABI in the first place.  Otherwise, people check
> git log will be confused by ABI broken.  This makes it easier to be
> reviewed too.
> 

This is a result of fixing alignment/holes (suggested by Arnd) and my
not dropping policy_node, which I'd originally planned to do.

I figured that whenever we decided to move forward, mempolicy2 and
mbind2 syscalls would end up squashed into a single commit for the
purpose of ensuring the feature goes in as a whole.  I can fix this
though.

~Gregory