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

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Message-ID: <2eab8e20-a87d-a5be-5d55-cdaa0b377b1d@redhat.com>
Date:   Thu, 11 Jul 2019 12:52:19 -0400
From:   Nitesh Narayan Lal <nitesh@...hat.com>
To:     Dave Hansen <dave.hansen@...el.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 12:45 PM, Dave Hansen wrote:
> 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?
Yes. However, the base_pfn and end_pfn will be updated with the zone1's
base and zone2s end_pfn value from page_hinting_enable(). Isn't?

-- 
Thanks
Nitesh