linux-kernel - [PATCH v4 4/9] mm/page_alloc.c: allow oversized movablecore

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Date:   Fri, 10 Mar 2023 16:38:50 -0800
From:   Doug Berger <opendmb@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Jonathan Corbet <corbet@....net>, Mike Rapoport <rppt@...nel.org>,
        Borislav Petkov <bp@...e.de>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Damien Le Moal <damien.lemoal@...nsource.wdc.com>,
        Kim Phillips <kim.phillips@....com>,
        "Steven Rostedt (Google)" <rostedt@...dmis.org>,
        Michal Hocko <mhocko@...e.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
        Mel Gorman <mgorman@...e.de>,
        Muchun Song <songmuchun@...edance.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        David Hildenbrand <david@...hat.com>,
        Oscar Salvador <osalvador@...e.de>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Sukadev Bhattiprolu <quic_sukadev@...cinc.com>,
        Rik van Riel <riel@...riel.com>,
        Roman Gushchin <guro@...com>, Minchan Kim <minchan@...nel.org>,
        Chris Goldsworthy <quic_cgoldswo@...cinc.com>,
        "Georgi Djakov" <quic_c_gdjako@...cinc.com>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Doug Berger <opendmb@...il.com>
Subject: [PATCH v4 4/9] mm/page_alloc.c: allow oversized movablecore

Now that the error in computation of corepages has been corrected
by commit 9fd745d450e7 ("mm: fix overflow in
find_zone_movable_pfns_for_nodes()"), oversized specifications of
movablecore will result in a zero value for required_kernelcore if
it is not also specified.

It is unintuitive for such a request to lead to no ZONE_MOVABLE
memory when the kernel parameters are clearly requesting some.

The current behavior when requesting an oversized kernelcore is to
classify all of the pages in movable_zone as kernelcore. The new
behavior when requesting an oversized movablecore (when not also
specifying kernelcore) is to similarly classify all of the pages
in movable_zone as movablecore.

Signed-off-by: Doug Berger <opendmb@...il.com>
---
 mm/page_alloc.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 827b4bfef625..e574c6a79e2f 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -8166,13 +8166,13 @@ static void __init find_zone_movable_pfns_for_nodes(void)
 		corepages = totalpages - required_movablecore;
 
 		required_kernelcore = max(required_kernelcore, corepages);
+	} else if (!required_kernelcore) {
+		/* If kernelcore was not specified, there is no ZONE_MOVABLE */
+		goto out;
 	}
 
-	/*
-	 * If kernelcore was not specified or kernelcore size is larger
-	 * than totalpages, there is no ZONE_MOVABLE.
-	 */
-	if (!required_kernelcore || required_kernelcore >= totalpages)
+	/* If kernelcore size exceeds totalpages, there is no ZONE_MOVABLE */
+	if (required_kernelcore >= totalpages)
 		goto out;
 
 	/* usable_startpfn is the lowest possible pfn ZONE_MOVABLE can be at */
-- 
2.34.1