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From:   js1304@gmail.com
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Michal Hocko <mhocko@kernel.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        "Aneesh Kumar K . V" <aneesh.kumar@linux.ibm.com>,
        kernel-team@lge.com, Joonsoo Kim <iamjoonsoo.kim@lge.com>
Subject: [PATCH for v5.9] mm/page_alloc: handle a missing case for memalloc_nocma_{save/restore} APIs
Date:   Tue, 25 Aug 2020 13:59:42 +0900
Message-Id: <1598331582-19923-1-git-send-email-iamjoonsoo.kim@lge.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

From: Joonsoo Kim <iamjoonsoo.kim@lge.com>

memalloc_nocma_{save/restore} APIs can be used to skip page allocation
on CMA area, but, there is a missing case and the page on CMA area could
be allocated even if APIs are used. This patch handles this case to fix
the potential issue.

Missing case is an allocation from the pcplist. MIGRATE_MOVABLE pcplist
could have the pages on CMA area so we need to skip it if ALLOC_CMA isn't
specified.

This patch implements this behaviour by checking allocated page from
the pcplist rather than skipping an allocation from the pcplist entirely.
Skipping the pcplist entirely would result in a mismatch between watermark
check and actual page allocation. And, it requires to break current code
layering that order-0 page is always handled by the pcplist. I'd prefer
to avoid it so this patch uses different way to skip CMA page allocation
from the pcplist.

Fixes: 8510e69c8efe (mm/page_alloc: fix memalloc_nocma_{save/restore} APIs)
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
---
 mm/page_alloc.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 0e2bab4..c4abf58 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3341,6 +3341,22 @@ static struct page *rmqueue_pcplist(struct zone *preferred_zone,
 	pcp = &this_cpu_ptr(zone->pageset)->pcp;
 	list = &pcp->lists[migratetype];
 	page = __rmqueue_pcplist(zone,  migratetype, alloc_flags, pcp, list);
+#ifdef CONFIG_CMA
+	if (page) {
+		int mt = get_pcppage_migratetype(page);
+
+		/*
+		 * pcp could have the pages on CMA area and we need to skip it
+		 * when !ALLOC_CMA. Free all pcplist and retry allocation.
+		 */
+		if (is_migrate_cma(mt) && !(alloc_flags & ALLOC_CMA)) {
+			list_add(&page->lru, &pcp->lists[migratetype]);
+			pcp->count++;
+			free_pcppages_bulk(zone, pcp->count, pcp);
+			page = __rmqueue_pcplist(zone, migratetype, alloc_flags, pcp, list);
+		}
+	}
+#endif
 	if (page) {
 		__count_zid_vm_events(PGALLOC, page_zonenum(page), 1);
 		zone_statistics(preferred_zone, zone);
-- 
2.7.4