linux-kernel - Re: [v3 PATCH 0/3] mm/mempolicy: some fix and semantics cleanup

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Date:   Tue, 1 Jun 2021 08:55:13 +0800
From:   Feng Tang <feng.tang@...el.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, Michal Hocko <mhocko@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Ben Widawsky <ben.widawsky@...el.com>,
        linux-kernel@...r.kernel.org,
        Andrea Arcangeli <aarcange@...hat.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Andi Kleen <ak@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>, ying.huang@...el.com
Subject: Re: [v3 PATCH 0/3] mm/mempolicy: some fix and semantics cleanup

Hi Andrew,

Thanks for reviewing and taking the patches.

On Mon, May 31, 2021 at 02:41:28PM -0700, Andrew Morton wrote:
> On Mon, 31 May 2021 22:05:53 +0800 Feng Tang <feng.tang@...el.com> wrote:
> 
> > We've posted v4 patchset introducing a new "perfer-many" memory policy
> > https://lore.kernel.org/lkml/1615952410-36895-1-git-send-email-feng.tang@intel.com/ ,
> > for which Michal Hocko gave many comments while pointing out some
> > problems, and we also found some semantics confusion about 'prefer'
> > and 'local' policy, as well as some duplicated code. This patchset
> > tries to address them. Please help to review, thanks!
> > 
> > The patchset has been run with some sanity test like 'stress-ng'
> > and 'ltp', and no problem found.
> 
> None of the above is suitable for the [0/n] overall description.  I
> copied-n-pasted the v1 cover letter from the above link.  Please check
> that it is all still correct and up to date.  If not, please send along
> replacement text, thanks.

I should make the cover-letter more descriptive. The link above is another
patchset to introduce a new memory policy MPOL_PREFERRED_MANY, while these
3 patches are preparation work for it, to make it easier for a new policy
to be hooked in.

So how about the following text:

Current memory policy code has some confusing and ambiguous part about
MPOL_LOCAL policy, as it is handled as a faked MPOL_PREFERRED one, and
there are many places having to distinguish them. Also the nodemask
intersection check needs cleanup to be more explicit for OOM use, and
handle MPOL_INTERLEAVE correctly. This patchset cleans up these and
unifies the parameter sanity check for mbind() and set_mempolicy().

Please feel free to modify it, thanks!

- Feng