linux-kernel - Re: [PATCH v7 3/5] mm/hugetlb: add support for mempolicy MPOL_PREFERRED

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Date:   Mon, 9 Aug 2021 10:41:40 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Feng Tang <feng.tang@...el.com>
Cc:     linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        David Rientjes <rientjes@...gle.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Ben Widawsky <ben.widawsky@...el.com>,
        linux-kernel@...r.kernel.org, linux-api@...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: [PATCH v7 3/5] mm/hugetlb: add support for mempolicy
 MPOL_PREFERRED_MANY

On Mon 09-08-21 10:44:30, Feng Tang wrote:
> Hi Michal,
> 
> Thanks for the review and ACKs to 1/5 and 2/5 patches.
> 
> On Fri, Aug 06, 2021 at 03:35:48PM +0200, Michal Hocko wrote:
> > On Tue 03-08-21 13:59:20, Feng Tang wrote:
> > > From: Ben Widawsky <ben.widawsky@...el.com>
> > > 
> > > Implement the missing huge page allocation functionality while obeying
> > > the preferred node semantics. This is similar to the implementation
> > > for general page allocation, as it uses a fallback mechanism to try
> > > multiple preferred nodes first, and then all other nodes.
> > > 
> > > [akpm: fix compling issue when merging with other hugetlb patch]
> > > [Thanks to 0day bot for catching the missing #ifdef CONFIG_NUMA issue]
> > > Link: https://lore.kernel.org/r/20200630212517.308045-12-ben.widawsky@intel.com
> > > Suggested-by: Michal Hocko <mhocko@...e.com>
> > > Signed-off-by: Ben Widawsky <ben.widawsky@...el.com>
> > > Co-developed-by: Feng Tang <feng.tang@...el.com>
> > > Signed-off-by: Feng Tang <feng.tang@...el.com>
> > 
> > ifdefery is just ugly as hell. One way to get rid of that would be to
> > provide a mpol_is_preferred_many() wrapper and hide the CONFIG_NUMA in
> > mempolicy.h. I haven't checked but this might help to remove some other
> > ifdefery as well.
> > 
> > I especially dislike the label hidden in the ifdef. You can get rid of
> > that by checking the page for NULL.
> 
> Yes, the 'ifdef's were annoying to me too, and thanks for the suggestions.
> Following is the revised patch upon the suggestion.
> 
> Thanks,
> Feng
> 
> -------8<---------------------
> 
> >From fc30718c40f02ba5ea73456af49173e66b5032c1 Mon Sep 17 00:00:00 2001
> From: Ben Widawsky <ben.widawsky@...el.com>
> Date: Thu, 5 Aug 2021 23:01:11 -0400
> Subject: [PATCH] mm/hugetlb: add support for mempolicy MPOL_PREFERRED_MANY
> 
> Implement the missing huge page allocation functionality while obeying the
> preferred node semantics.  This is similar to the implementation for
> general page allocation, as it uses a fallback mechanism to try multiple
> preferred nodes first, and then all other nodes. 
> 
> To avoid adding too many "#ifdef CONFIG_NUMA" check, add a helper function
> in mempolicy.h to check whether a mempolicy is MPOL_PREFERRED_MANY.
> 
> [akpm: fix compling issue when merging with other hugetlb patch]
> [Thanks to 0day bot for catching the !CONFIG_NUMA compiling issue]
> [Michal Hocko: suggest to remove the #ifdef CONFIG_NUMA check]
> Link: https://lore.kernel.org/r/20200630212517.308045-12-ben.widawsky@intel.com
> Link: https://lkml.kernel.org/r/1627970362-61305-4-git-send-email-feng.tang@intel.com
> Suggested-by: Michal Hocko <mhocko@...e.com>
> Signed-off-by: Ben Widawsky <ben.widawsky@...el.com>
> Co-developed-by: Feng Tang <feng.tang@...el.com>
> Signed-off-by: Feng Tang <feng.tang@...el.com>

Yeah. This looks much better. Thanks!
Acked-by: Michal Hocko <mhocko@...e.com>
Do you think you can provide same helpers for other policies as well?
Maybe we can get rid of some other ifdefery as well.

Thanks!
-- 
Michal Hocko
SUSE Labs