linux-kernel - Re: [PATCH] mm/page_alloc: return 0 in case this node has no page within the zone

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Message-ID: <20170209135929.GA59297@WeideMacBook-Pro.local>
Date:   Thu, 9 Feb 2017 21:59:29 +0800
From:   Wei Yang <richard.weiyang@...il.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Wei Yang <richard.weiyang@...il.com>, akpm@...ux-foundation.org,
        vbabka@...e.cz, mgorman@...hsingularity.net, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/page_alloc: return 0 in case this node has no page
 within the zone

On Tue, Feb 07, 2017 at 04:41:21PM +0100, Michal Hocko wrote:
>On Tue 07-02-17 23:32:47, Wei Yang wrote:
>> On Tue, Feb 07, 2017 at 10:45:57AM +0100, Michal Hocko wrote:
>[...]
>> >Is there any reason why for_each_mem_pfn_range cannot be changed to
>> >honor the given start/end pfns instead? I can imagine that a small zone
>> >would see a similar pointless iterations...
>> >
>> 
>> Hmm... No special reason, just not thought about this implementation. And
>> actually I just do the similar thing as in zone_spanned_pages_in_node(), in
>> which also return 0 when there is no overlap.
>> 
>> BTW, I don't get your point. You wish to put the check in
>> for_each_mem_pfn_range() definition?
>
>My point was that you are handling one special case (an empty zone) but
>the underlying problem is that __absent_pages_in_range might be wasting
>cycles iterating over memblocks that are way outside of the given pfn
>range. At least this is my understanding. If you fix that you do not
>need the special case, right?
>-- 
>Michal Hocko
>SUSE Labs

> Not really, sorry, this area is full of awkward and subtle code when new
> changes build on top of previous awkwardness/surprises. Any cleanup
> would be really appreciated. That is the reason I didn't like the
> initial check all that much.

Looks my fetchmail failed to get your last reply. So I copied it here.

Yes, the change here looks not that nice, while currently this is what I can't
come up with.

Thanks for your review :-)

-- 
Wei Yang
Help you, Help me

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