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

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Date:   Wed, 5 Feb 2020 22:48:11 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Wei Yang <richardw.yang@...ux.intel.com>
Cc:     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()

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?

> 	}
> 
> 

Like this, I believe both David and I will be satisfactory. Even though
I still think his 2nd resetting is not needed :-)

> 	/* The zone has no valid section */
> 	if (!pfn) {
> 			zone->zone_start_pfn = 0;
> 			zone->spanned_pages = 0;
> 	}
> 
> out:
> 	zone_span_writeunlock(zone);
> 
> Well, this is just my personal taste :-)
> 
> >-
> >-	/*
> >-	 * The section is not biggest or smallest mem_section in the zone, it
> >-	 * only creates a hole in the zone. So in this case, we need not
> >-	 * change the zone. But perhaps, the zone has only hole data. Thus
> >-	 * it check the zone has only hole or not.
> >-	 */
> >-	pfn = zone_start_pfn;
> >-	for (; pfn < zone_end_pfn; pfn += PAGES_PER_SUBSECTION) {
> >-		if (unlikely(!pfn_to_online_page(pfn)))
> >-			continue;
> >-
> >-		if (page_zone(pfn_to_page(pfn)) != zone)
> >-			continue;
> >-
> >-		/* Skip range to be removed */
> >-		if (pfn >= start_pfn && pfn < end_pfn)
> >-			continue;
> >-
> >-		/* If we find valid section, we have nothing to do */
> >-		zone_span_writeunlock(zone);
> >-		return;
> >-	}
> >-
> >-	/* The zone has no valid section */
> >-	zone->zone_start_pfn = 0;
> >-	zone->spanned_pages = 0;
> > 	zone_span_writeunlock(zone);
> > }
> > 
> >-- 
> >2.21.0
> 
> -- 
> Wei Yang
> Help you, Help me
>