linux-kernel - Re: [PATCH v6 08/10] mm/memory_hotplug: Don't check for "all holes" in shrink_zone

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Message-ID: <20200205232620.GC28446@richard>
Date:   Thu, 6 Feb 2020 07:26:20 +0800
From:   Wei Yang <richardw.yang@...ux.intel.com>
To:     Baoquan He <bhe@...hat.com>
Cc:     Wei Yang <richardw.yang@...ux.intel.com>,
        David Hildenbrand <david@...hat.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-arm-kernel@...ts.infradead.org, linux-ia64@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
        linux-sh@...r.kernel.org, x86@...nel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <osalvador@...e.de>,
        Michal Hocko <mhocko@...e.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH v6 08/10] mm/memory_hotplug: Don't check for "all holes"
 in shrink_zone_span()

On Thu, Feb 06, 2020 at 07:08:26AM +0800, Baoquan He wrote:
>On 02/06/20 at 06:56am, Wei Yang wrote:
>> On Wed, Feb 05, 2020 at 10:48:11PM +0800, Baoquan He wrote:
>> >Hi Wei Yang,
>> >
>> >On 02/05/20 at 05:59pm, Wei Yang wrote:
>> >> >diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> >> >index f294918f7211..8dafa1ba8d9f 100644
>> >> >--- a/mm/memory_hotplug.c
>> >> >+++ b/mm/memory_hotplug.c
>> >> >@@ -393,6 +393,9 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
>> >> > 		if (pfn) {
>> >> > 			zone->zone_start_pfn = pfn;
>> >> > 			zone->spanned_pages = zone_end_pfn - pfn;
>> >> >+		} else {
>> >> >+			zone->zone_start_pfn = 0;
>> >> >+			zone->spanned_pages = 0;
>> >> > 		}
>> >> > 	} else if (zone_end_pfn == end_pfn) {
>> >> > 		/*
>> >> >@@ -405,34 +408,11 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
>> >> > 					       start_pfn);
>> >> > 		if (pfn)
>> >> > 			zone->spanned_pages = pfn - zone_start_pfn + 1;
>> >> >+		else {
>> >> >+			zone->zone_start_pfn = 0;
>> >> >+			zone->spanned_pages = 0;
>> >> >+		}
>> >> > 	}
>> >> 
>> >> If it is me, I would like to take out these two similar logic out.
>> >
>> >I also like this style. 
>> >> 
>> >> For example:
>> >> 
>> >> 	if () {
>> >> 	} else if () {
>> >> 	} else {
>> >> 		goto out;
>> >Here the last else is unnecessary, right?
>> >
>> 
>> I am afraid not.
>> 
>> If the range is not the first or last, we would leave pfn not initialized.
>
>Ah, you are right. I forgot that one. Then pfn can be assigned the
>zone_start_pfn as the old code. Then the following logic is the same
>as the original code, find_smallest_section_pfn()/find_biggest_section_pfn() 
>have done the iteration the old for loop was doing.
>
>	unsigned long pfn = zone_start_pfn;	
>	if () {
>	} else if () {
>	} 
>
>	/* The zone has no valid section */
>	if (!pfn) {
>        	zone->zone_start_pfn = 0;
>        	zone->spanned_pages = 0;
>	}

This one look better :-)

Thanks

-- 
Wei Yang
Help you, Help me