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

From: Feng Tang <feng.tang@intel.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org, Michal Hocko <mhocko@kernel.org>,
	David Rientjes <rientjes@google.com>,
	Dave Hansen <dave.hansen@intel.com>,
	Ben Widawsky <ben.widawsky@intel.com>,
	linux-kernel@vger.kernel.org,
	Andrea Arcangeli <aarcange@redhat.com>,
	Mel Gorman <mgorman@techsingularity.net>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Randy Dunlap <rdunlap@infradead.org>,
	Vlastimil Babka <vbabka@suse.cz>, Andi Kleen <ak@linux.intel.com>,
	Dan Williams <dan.j.williams@intel.com>,
	ying.huang@intel.com
Subject: Re: [v3 PATCH 0/3] mm/mempolicy: some fix and semantics cleanup
Date: Tue, 1 Jun 2021 08:55:13 +0800	[thread overview]
Message-ID: <20210601005513.GA15828@shbuild999.sh.intel.com> (raw)
In-Reply-To: <20210531144128.e69aaf2904e83ae170f00f06@linux-foundation.org>

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@intel.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