linux-kernel - Re: [RFC][Patch v11 1/2] mm: page

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Message-ID: <719ac813-01d7-7602-0951-6c90f1f7efc1@intel.com>
Date:   Thu, 11 Jul 2019 09:45:11 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Nitesh Narayan Lal <nitesh@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        pbonzini@...hat.com, lcapitulino@...hat.com, pagupta@...hat.com,
        wei.w.wang@...el.com, yang.zhang.wz@...il.com, riel@...riel.com,
        david@...hat.com, mst@...hat.com, dodgen@...gle.com,
        konrad.wilk@...cle.com, dhildenb@...hat.com, aarcange@...hat.com,
        alexander.duyck@...il.com, john.starks@...rosoft.com,
        mhocko@...e.com
Subject: Re: [RFC][Patch v11 1/2] mm: page_hinting: core infrastructure

On 7/11/19 9:36 AM, Nitesh Narayan Lal wrote:
>>>>> +struct zone_free_area {
>>>>> +	unsigned long *bitmap;
>>>>> +	unsigned long base_pfn;
>>>>> +	unsigned long end_pfn;
>>>>> +	atomic_t free_pages;
>>>>> +	unsigned long nbits;
>>>>> +} free_area[MAX_NR_ZONES];
>>>> Why do we need an extra data structure.  What's wrong with putting
>>>> per-zone data in ... 'struct zone'?
>>> Will it be acceptable to add fields in struct zone, when they will only
>>> be used by page hinting?
>> Wait a sec...  MAX_NR_ZONES the number of zone types not the maximum
>> number of *zones* in the system.
>>
>> Did you test this on a NUMA system?
> Yes, I tested it with a guest having 2 and 3 NUMA nodes.

How can this *possibly* have worked?

Won't each same-typed zone just use the same free_area[] entry since
zone_idx(zone1)==zone_idx(zone2) if zone1 and zone2 are (for example)
both ZONE_NORMAL?