linux-kernel - [PATCH] mm/page_alloc: consider pfn holes after pfn_valid() in __pageblock_pfn_to

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Message-Id: <62e231a8f2e50c04dcadc7a0cfaa6dea5ce1ec05.1681296022.git.baolin.wang@linux.alibaba.com>
Date:   Wed, 12 Apr 2023 18:45:31 +0800
From:   Baolin Wang <baolin.wang@...ux.alibaba.com>
To:     akpm@...ux-foundation.org
Cc:     mgorman@...hsingularity.net, vbabka@...e.cz, mhocko@...e.com,
        david@...hat.com, baolin.wang@...ux.alibaba.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: [PATCH] mm/page_alloc: consider pfn holes after pfn_valid() in __pageblock_pfn_to_page()

Now the __pageblock_pfn_to_page() is used by set_zone_contiguous(),
which checks whether the given zone contains holes, and uses pfn_valid()
to check if the end pfn is valid. However pfn_valid() can not make sure
the end pfn is not a hole if the size of a pageblock is larger than the
size of a sub-mem_section, since the struct page getting by pfn_to_page()
may represent a hole or an unusable page frame, which may cause incorrect
zone contiguous is set.

Though another user of pageblock_pfn_to_page() in compaction seems work
well now, it is better to avoid scanning or touching these offline pfns.
So like commit 2d070eab2e82 ("mm: consider zone which is not fully
populated to have holes"), we should also use pfn_to_online_page() for
the end pfn to make sure it is a valid pfn with usable page frame.
Meanwhile the pfn_valid() for end pfn can be dropped now.

Moreover we've already used pfn_to_online_page() for start pfn to make
sure it is online and valid, so the pfn_valid() for the start pfn is
unnecessary, drop it.

Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
---
 mm/page_alloc.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d0eb280ec7e4..8076f519c572 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1512,9 +1512,6 @@ struct page *__pageblock_pfn_to_page(unsigned long start_pfn,
 	/* end_pfn is one past the range we are checking */
 	end_pfn--;

-	if (!pfn_valid(start_pfn) || !pfn_valid(end_pfn))
-		return NULL;
-
 	start_page = pfn_to_online_page(start_pfn);
 	if (!start_page)
 		return NULL;
@@ -1522,7 +1519,9 @@ struct page *__pageblock_pfn_to_page(unsigned long start_pfn,
 	if (page_zone(start_page) != zone)
 		return NULL;

-	end_page = pfn_to_page(end_pfn);
+	end_page = pfn_to_online_page(end_pfn);
+	if (!end_page)
+		return NULL;

 	/* This gives a shorter code than deriving page_zone(end_page) */
 	if (page_zone_id(start_page) != page_zone_id(end_page))
-- 
2.27.0