From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 41B753B9920 for ; Wed, 26 Aug 2026 08:27:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787732844; cv=none; b=TEFqmi3Qqegi50BkczUcdkJ1ujTgzDUuGruhWSB05WWP0n3fz4XL2Sa0qh/DcYkKzhZxQN3hsE+47z2K/r5rpA2UHzYWCmdt2ky5zHGRTJkzxpyZOgB2bL5TsqYSOtVju8B3lFT0wMhtIrUzzSIhMSwRAG97LQtYcYUaKoQc2xU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787732844; c=relaxed/simple; bh=gYK+vzm5P2C4B3dAPzL7PpgMYYgzo6mT/a3Ge8C0M7A=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Hu5yBygLayJKreVPcrVSs4kQobwVhoW+edtwwnUwYYni/40b+/QO9B/eU/abrgw5sTGf9rwD++Rtdym7+2UppWZEeNFBZ062DV7Wy5Jq46fsIHOHkopnwnFHzNZDbEu0bfdagEUpyw1/OxzIk4TxXWjk8UI98MEDY3N4ahtqHqc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=eyN+e6X4; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="eyN+e6X4" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9283A1F00A3A; Wed, 26 Aug 2026 08:27:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787732836; bh=L4VXwukOvzmoVUjOHFr+/WSXxAsaSNTt7jYsFS0Y3YQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=eyN+e6X4tm2Lp7KCNpBGiVXo1xBpSrkAzJ4DEe+2iUAPt86j9ZkhDC0cfxFTHhgay no/k/Auzl7iLDhRJZKqv0wn3dOmIl7Ejo+to1t0zhjJ3ONQ4lHECKlAZfVXEAz2mu/ 0bLuuVxW1ot9fyc5u17BSJ2JE0y1ENfGc8RTtzQAY4Ppdt+eREuIQLIvNGmrs2ouYb BLrBzaiTXBddrLxNOhVvHb4TuHmEO8Gz78AFrBvUi4OQ0yj5T8cefv4FyQOobCggGJ eLWHOkTn8BuoFxluLX88uMOI6MhYXVuBE0YzfR+4WcPbMryCmQjzIRmspHlcn8Mf29 XdM2g4d1PTR1w== Message-ID: <63a72a5c-6e24-4513-a83c-d8f63df3a600@kernel.org> Date: Wed, 26 Aug 2026 10:27:12 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v3 0/8] batch lookups in follow_page_mask() To: Christoph Hellwig , Rik van Riel Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, Andrew Morton , Jason Gunthorpe , John Hubbard , Peter Xu , linux-mm@kvack.org References: <20260811025157.1632867-1-riel@surriel.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 8/26/26 09:35, Christoph Hellwig wrote: > On Tue, Aug 25, 2026 at 09:39:14PM -0700, Christoph Hellwig wrote: >> The other callers of iov_iter_extract_bvecs matter more, but this is >> the main user. >> >> And iov_iter_extract_bvecs right now is very inefficient when used >> on larger folios, as each call to iov_iter_extract_bvecs and thus >> iov_iter_extract_pages and iov_iter_extract_user_pages can only >> fill in up to 256 pages. On x86 that is a single PMD mapped >> folio. Passing down the bio_vec array means that for PMD-mapped >> ranges we reduce the calls into pin_user_pages_fast by a factor >> of 256. > > Also in addition to reducing the calls to pin_user_pages_fast, it also > removes a fair amount of work to recalculate the bio_len in the > get_contig_folio_len loop in iov_iter_extract_bvecs, which has shown up > in profiles (although only marginally so). We could think of a mechanism that fills a given structure in a better way, and I think we recently discussed returning folio ranges, and might to that through something like phyr (or however that is called :) ). But that's really not something is would mix into this work here. -- Cheers, David