linux-kernel - [PATCH] mm,cma: remove pfn_range_valid

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Date:   Fri, 6 Mar 2020 17:06:47 -0500
From:   Rik van Riel <riel@...riel.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kernel-team@...com, Anshuman Khandual <anshuman.khandual@....com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Vlastimil Babka <vbabka@...e.cz>, Qian Cai <cai@....pw>,
        Roman Gushchin <guro@...com>
Subject: [PATCH] mm,cma: remove pfn_range_valid_contig

The function pfn_range_valid_contig checks whether all memory in the
target area is free. This causes unnecessary CMA failures, since
alloc_contig_range will migrate movable memory out of a target range,
and has its own sanity check early on in has_unmovable_pages, which
is called from start_isolate_page_range & set_migrate_type_isolate.

Relying on that has_unmovable_pages call simplifies the CMA code and
results in an increased success rate of CMA allocations.

Signed-off-by: Rik van Riel <riel@...riel.com>
---
 mm/page_alloc.c | 47 +++--------------------------------------------
 1 file changed, 3 insertions(+), 44 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 0fb3c1719625..75e84907d8c6 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -8539,32 +8539,6 @@ static int __alloc_contig_pages(unsigned long start_pfn,
 				  gfp_mask);
 }
 
-static bool pfn_range_valid_contig(struct zone *z, unsigned long start_pfn,
-				   unsigned long nr_pages)
-{
-	unsigned long i, end_pfn = start_pfn + nr_pages;
-	struct page *page;
-
-	for (i = start_pfn; i < end_pfn; i++) {
-		page = pfn_to_online_page(i);
-		if (!page)
-			return false;
-
-		if (page_zone(page) != z)
-			return false;
-
-		if (PageReserved(page))
-			return false;
-
-		if (page_count(page) > 0)
-			return false;
-
-		if (PageHuge(page))
-			return false;
-	}
-	return true;
-}
-
 static bool zone_spans_last_pfn(const struct zone *zone,
 				unsigned long start_pfn, unsigned long nr_pages)
 {
@@ -8605,28 +8579,13 @@ struct page *alloc_contig_pages(unsigned long nr_pages, gfp_t gfp_mask,
 	zonelist = node_zonelist(nid, gfp_mask);
 	for_each_zone_zonelist_nodemask(zone, z, zonelist,
 					gfp_zone(gfp_mask), nodemask) {
-		spin_lock_irqsave(&zone->lock, flags);
-
 		pfn = ALIGN(zone->zone_start_pfn, nr_pages);
 		while (zone_spans_last_pfn(zone, pfn, nr_pages)) {
-			if (pfn_range_valid_contig(zone, pfn, nr_pages)) {
-				/*
-				 * We release the zone lock here because
-				 * alloc_contig_range() will also lock the zone
-				 * at some point. If there's an allocation
-				 * spinning on this lock, it may win the race
-				 * and cause alloc_contig_range() to fail...
-				 */
-				spin_unlock_irqrestore(&zone->lock, flags);
-				ret = __alloc_contig_pages(pfn, nr_pages,
-							gfp_mask);
-				if (!ret)
-					return pfn_to_page(pfn);
-				spin_lock_irqsave(&zone->lock, flags);
-			}
+			ret = __alloc_contig_pages(pfn, nr_pages, gfp_mask);
+			if (!ret)
+				return pfn_to_page(pfn);
 			pfn += nr_pages;
 		}
-		spin_unlock_irqrestore(&zone->lock, flags);
 	}
 	return NULL;
 }
-- 
2.24.1