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: <20200205233428.GD28446@richard>
Date:   Thu, 6 Feb 2020 07:34:28 +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 07:30:51AM +0800, Baoquan He wrote:
>On 02/06/20 at 07:26am, Wei Yang wrote:
>> 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 for your confirmation, I will make one patch like this and post.

Sure :-)

-- 
Wei Yang
Help you, Help me