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Tue, 23 Sep 2025 17:05:28 -0700 (PDT) Date: Wed, 24 Sep 2025 00:05:28 +0000 From: Wei Yang To: Michal Hocko Cc: Wei Yang , akpm@linux-foundation.org, vbabka@suse.cz, surenb@google.com, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com, david@redhat.com, anshuman.khandual@arm.com, linux-mm@kvack.org, dev.jain@arm.com, Oscar Salvador Subject: Re: [PATCH] mm/page_alloc: fix alignment for alloc_contig_pages_noprof() Message-ID: <20250924000528.plhmkfn4qnx44a6x@master> Reply-To: Wei Yang References: <20250923001943.2479-1-richard.weiyang@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170113 (1.7.2) X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 4A55E180003 X-Stat-Signature: zhmwbqwfdu6mix8cmmxwiz7xbu66dmzx X-HE-Tag: 1758672331-530141 X-HE-Meta: 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 df0XbraI 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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: On Tue, Sep 23, 2025 at 09:29:12AM +0200, Michal Hocko wrote: >On Tue 23-09-25 00:19:43, Wei Yang wrote: >> Commit 5e27a2df03b8 ("mm/page_alloc: add alloc_contig_pages()") >> introduced generic method for alloc_contig_pages(). But the alignment >> calculation seems wrong. >> >> Since ALIGN() only accept power of two value, while nr_pages could be >> any positive one, the result is not defined. >> >> Use roundup() to calculate the correct alignment. > >What is the problem you are trying to fix here? The ALIGN is certainly >not well defined for nr_pages that is not power of two but does any >caller of alloc_contig_pages assumes any specific alignment, especially >when nr_pages is not power of two? > There is no real problem here. The initial thought is ALIGN() don't expect non-power_of_two value. The discussion above sounds reasonable, we don't need alignment for non-power_of_two nr_pages. So this looks we can start iteration from zone->zone_start_pfn for non-power_of_two nr_pages. IMHO, How about the change below? pfn = zone->zone_start_pfn; if (is_power_of_2(nr_pages)) pfn = ALIGN(pfn, nr_pages) And it looks making code consist with the doc above. -- Wei Yang Help you, Help me