linux-kernel - Re: [PATCH] mm/isolation: Remove redundant pfn_valid_within() in __first_valid

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Message-ID: <8a6b3968-a315-07ce-0491-2a5acdd49ab4@arm.com>
Date:   Thu, 21 Mar 2019 13:43:40 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Zi Yan <ziy@...dia.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, mike.kravetz@...cle.com,
        osalvador@...e.de, akpm@...ux-foundation.org
Subject: Re: [PATCH] mm/isolation: Remove redundant pfn_valid_within() in
 __first_valid_page()



On 03/21/2019 01:37 PM, Michal Hocko wrote:
> On Thu 21-03-19 11:03:18, Anshuman Khandual wrote:
>>
>>
>> On 03/21/2019 10:31 AM, Zi Yan wrote:
>>> On 20 Mar 2019, at 21:13, Anshuman Khandual wrote:
>>>
>>>> pfn_valid_within() calls pfn_valid() when CONFIG_HOLES_IN_ZONE making it
>>>> redundant for both definitions (w/wo CONFIG_MEMORY_HOTPLUG) of the helper
>>>> pfn_to_online_page() which either calls pfn_valid() or pfn_valid_within().
>>>> pfn_valid_within() being 1 when !CONFIG_HOLES_IN_ZONE is irrelevant either
>>>> way. This does not change functionality.
>>>>
>>>> Fixes: 2ce13640b3f4 ("mm: __first_valid_page skip over offline pages")
>>>
>>> I would not say this patch fixes the commit 2ce13640b3f4 from 2017,
>>> because the pfn_valid_within() in pfn_to_online_page() was introduced by
>>> a recent commit b13bc35193d9e last month. :)
>>
>> Right, will update the tag with this commit.
> 
> The patch is correct but I wouldn't bother to add Fixes tag at all. The
> current code is obviously not incorrect. Do you see any actual

Sure.

> performance issue?
> 

No. Just from code inspection. pfn_valid() is anyways expensive on arm64
because of the memblock search so why to make it redundant as well.