linux-kernel - [PATCH v10 2/8] mm,memory_hotplug: Relax fully spanned sections check

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Message-Id: <20210421102701.25051-3-osalvador@suse.de>
Date:   Wed, 21 Apr 2021 12:26:55 +0200
From:   Oscar Salvador <osalvador@...e.de>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     David Hildenbrand <david@...hat.com>,
        Michal Hocko <mhocko@...nel.org>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Pavel Tatashin <pasha.tatashin@...een.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Oscar Salvador <osalvador@...e.de>
Subject: [PATCH v10 2/8] mm,memory_hotplug: Relax fully spanned sections check

We want {online,offline}_pages to operate on whole memblocks, but
memmap_on_memory will poke pageblock_nr_pages aligned holes in the
beginning, which is a special case we want to allow.
Relax the check to account for that case.

Signed-off-by: Oscar Salvador <osalvador@...e.de>
Reviewed-by: David Hildenbrand <david@...hat.com>
Acked-by: Michal Hocko <mhocko@...e.com>
---
 mm/memory_hotplug.c | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 0cdbbfbc5757..e6aafd17a01a 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -838,9 +838,16 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
 	int ret;
 	struct memory_notify arg;
 
-	/* We can only online full sections (e.g., SECTION_IS_ONLINE) */
+	/*
+	 * {on,off}lining is constrained to full memory sections (or more
+	 * precisly to memory blocks from the user space POV).
+	 * memmap_on_memory is an exception because it reserves initial part
+	 * of the physical memory space for vmemmaps. That space is pageblock
+	 * aligned.
+	 */
 	if (WARN_ON_ONCE(!nr_pages ||
-			 !IS_ALIGNED(pfn | nr_pages, PAGES_PER_SECTION)))
+			 !IS_ALIGNED(pfn, pageblock_nr_pages) ||
+			 !IS_ALIGNED(pfn + nr_pages, PAGES_PER_SECTION)))
 		return -EINVAL;
 
 	mem_hotplug_begin();
@@ -1573,9 +1580,16 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages)
 	int ret, node;
 	char *reason;
 
-	/* We can only offline full sections (e.g., SECTION_IS_ONLINE) */
+	/*
+	 * {on,off}lining is constrained to full memory sections (or more
+	 * precisly to memory blocks from the user space POV).
+	 * memmap_on_memory is an exception because it reserves initial part
+	 * of the physical memory space for vmemmaps. That space is pageblock
+	 * aligned.
+	 */
 	if (WARN_ON_ONCE(!nr_pages ||
-			 !IS_ALIGNED(start_pfn | nr_pages, PAGES_PER_SECTION)))
+			 !IS_ALIGNED(start_pfn, pageblock_nr_pages) ||
+			 !IS_ALIGNED(start_pfn + nr_pages, PAGES_PER_SECTION)))
 		return -EINVAL;
 
 	mem_hotplug_begin();
-- 
2.16.3