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Wed, 03 Sep 2025 19:07:21 -0700 (PDT) Received: from localhost ([185.92.221.13]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-b047373b000sm173962166b.68.2025.09.03.19.07.20 (version=TLS1_2 cipher=ECDHE-ECDSA-CHACHA20-POLY1305 bits=256/256); Wed, 03 Sep 2025 19:07:20 -0700 (PDT) From: Wei Yang To: akpm@linux-foundation.org Cc: linux-mm@kvack.org, Wei Yang , Johannes Weiner , Zi Yan , David Hildenbrand , Baolin Wang , Vlastimil Babka Subject: [PATCH] mm/page_alloc: check the correct buddy if it is a starting block Date: Thu, 4 Sep 2025 02:06:54 +0000 Message-Id: <20250904020654.28689-1-richard.weiyang@gmail.com> X-Mailer: git-send-email 2.11.0 X-Stat-Signature: 7t8qbt4rqede3kr7c98csc4d39xcetcb X-Rspam-User: X-Rspamd-Queue-Id: 2EBDD4000A X-Rspamd-Server: rspam05 X-HE-Tag: 1756951642-754667 X-HE-Meta: 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 PFixU8lP 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: find_large_buddy() search buddy based on start_pfn, which maybe different from page's pfn, e.g. when page is not pageblock aligned, because prep_move_freepages_block() always align start_pfn to pageblock. This means when we found a starting block at start_pfn, it may check on the wrong page theoretically. The good news is the page passed to __move_freepages_block_isolate() has only two possible cases: * page is pageblock aligned * page is __first_valid_page() of this block So it is safe for the first case, and it won't get a buddy larger than pageblock for the second case. To eliminate the ambiguity, unify the handling for starting/tail block. Signed-off-by: Wei Yang Cc: Johannes Weiner Cc: Zi Yan Cc: David Hildenbrand Cc: Baolin Wang Cc: Vlastimil Babka --- Tried memory online/offine, which looks good. --- mm/page_alloc.c | 17 ++++------------- 1 file changed, 4 insertions(+), 13 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 5183a646fa09..453cd361386c 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -2093,6 +2093,7 @@ static bool __move_freepages_block_isolate(struct zone *zone, unsigned long start_pfn, pfn; int from_mt; int to_mt; + struct page *buddy; if (isolate == get_pageblock_isolate(page)) { VM_WARN_ONCE(1, "%s a pageblock that is already in that state", @@ -2107,10 +2108,10 @@ static bool __move_freepages_block_isolate(struct zone *zone, if (pageblock_order == MAX_PAGE_ORDER) goto move; - /* We're a tail block in a larger buddy */ pfn = find_large_buddy(start_pfn); - if (pfn != start_pfn) { - struct page *buddy = pfn_to_page(pfn); + buddy = pfn_to_page(pfn); + /* We're a part of a larger buddy */ + if (PageBuddy(buddy) && buddy_order(buddy) > pageblock_order) { int order = buddy_order(buddy); del_page_from_free_list(buddy, zone, order, @@ -2120,16 +2121,6 @@ static bool __move_freepages_block_isolate(struct zone *zone, return true; } - /* We're the starting block of a larger buddy */ - if (PageBuddy(page) && buddy_order(page) > pageblock_order) { - int order = buddy_order(page); - - del_page_from_free_list(page, zone, order, - get_pfnblock_migratetype(page, pfn)); - toggle_pageblock_isolate(page, isolate); - split_large_buddy(zone, page, pfn, order, FPI_NONE); - return true; - } move: /* Use MIGRATETYPE_MASK to get non-isolate migratetype */ if (isolate) { -- 2.34.1