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a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1768395588; bh=2ciTmIsSF6ir6Fs6b26xcjWBNYW3JUmbkKGuRcyQpPY=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=jZjS9zsCl13WtaMFQGlitZVCg2C6jZHZTbbylp9PT0iQ5yi0psg8M81wXlYXUH4i5 d3d+XtYyHVOzQjf9fEMATku1Kf+ZWMTvyI/iTWxhNG6OOQX+b/awgLPmuoDWUrsR1k Oh9o7C0QREl6zUz2W5nKIuObxCotCYsBYXhgcjE2PqO3aMVNsnC8+B1zxin1nzFAuP Tl8FkFtqGkB464MivgC9DqlJIrB3mM/GquDGxttTU7PIaDoQy5J/t2zbv7GfeAk0f6 OeEtt0cArfKOVVCAd9YhETcKP2hmMdvlWyVvQRSlx4NUtfKJLuBm60bBza1EE+G6y8 lgYpkjKoKN4yQ== Message-ID: <7f9fa27e-261f-4416-9a64-414d8130e5cb@kernel.org> Date: Wed, 14 Jan 2026 13:59:43 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/vmalloc: map contiguous pages in batches for vmap() whenever possible To: Barry Song <21cnbao@gmail.com>, Uladzislau Rezki Cc: akpm@linux-foundation.org, linux-mm@kvack.org, dri-devel@lists.freedesktop.org, jstultz@google.com, linaro-mm-sig@lists.linaro.org, linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, Barry Song , Sumit Semwal , Maxime Ripard , Tangquan Zheng References: <20251215053050.11599-1-21cnbao@gmail.com> From: "David Hildenbrand (Red Hat)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: C17F9A0005 X-Stat-Signature: emq5xh1xk7gotyew6ndx5utj3onfudd1 X-Rspam-User: X-HE-Tag: 1768395589-539263 X-HE-Meta: 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 gPhgCPQJ tAaBF6ekCOZLxGlq6DuJtkqCcqhawO4aRabgJGBRCutGUgX7OgKcNKWmvQbNNRQodcYrONNcXWOiVKrdstnVBRfPfa4dMTK81WMzO0fnGVOt0JhwKMQw17CnwBMahm1vut7AHDIrwDR6s1EOWe9/Mbx8ZXFgE/wNDWS/ehqxjxSolTvJJgEzzZeK0LIELbjDvaBKH8H6MSlIOkSJSdTpKUTkyL6sf9n8FoBLqGwZGZkGoWN2yB9v+8IbWRVMmpOZPOY5m 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 12/18/25 21:05, Barry Song wrote: > [...] >>> >>> +static inline int get_vmap_batch_order(struct page **pages, >>> + unsigned int stride, unsigned int max_steps, unsigned int idx) >>> +{ >>> + int nr_pages = 1; >>> + >>> + /* >>> + * Currently, batching is only supported in vmap_pages_range >>> + * when page_shift == PAGE_SHIFT. >>> + */ >>> + if (stride != 1) >>> + return 0; >>> + >>> + nr_pages = compound_nr(pages[idx]); >>> + if (nr_pages == 1) >>> + return 0; >>> + if (max_steps < nr_pages) >>> + return 0; >>> + >>> + if (num_pages_contiguous(&pages[idx], nr_pages) == nr_pages) >>> + return compound_order(pages[idx]); >>> + return 0; >>> +} >>> + >> Can we instead look at this as: it can be that we have continues >> set of pages let's find out. I mean if we do not stick just to >> compound pages. > > We use PageCompound(pages[0]) and compound_nr() as quick > filters to skip checking the contiguous count, and this is > now the intended use case. Always checking contiguity might > cause a slight regression, I guess. > > BTW, do we have a strong use case where GFP_COMP or folio is > not used, yet the pages are physically contiguous? It usually happens by accident :) E.g., allocate 2 pages and because we had to split an order-1 page into two order-0 pages, we get both of them. Using num_pages_contiguous() only might indeed be nicer, but then we have to add some handling for getting aligned ranges (start and size aligned to order) ... so not sure if that is worth it. -- Cheers David