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 D546040682C; Wed, 10 Jun 2026 13:18:57 +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=1781097538; cv=none; b=UsHs6Q5m45pnpzaZ9BNP7NI0qrvq93Mm5wixp2r8LEIS3QpLuOsr+yZGQlyDeTbkaeSPCujVqnk79Tu5YawdbRUqV9Zqr5EIW9PAySlIhlZ8m8/NWFfaWJuBo/NeStwWESNvih45fC7vXKWuc/8Emiwcuc9SUnjjxUQDGAr3VRk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781097538; c=relaxed/simple; bh=zbuH4UR3dnlhjbnJa2jGeabSZvijhj8ctrmpmF8Vf/Y=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=H1L3HfGbhHXV7rc0JtStXyya22XkFpCVuR7H2cIEpPbzJvGDtqegzDicAJ0L73s7wZHuxUe24fdgpjnOmjrasLhfQwMRRMjmW3/xLPe/kEC+m9IFxIVy7ZYk1rbZD+3D/V37G1E7ie1pfkZuVDWo3n0j290G5RPVwejE8HoD/QM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=OMEHcZsk; 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="OMEHcZsk" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E19C01F00893; Wed, 10 Jun 2026 13:18:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781097537; bh=zkNtDF+TnhAfuRsb9S+buKNiDb7dsGMnYzfKywwEPBo=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=OMEHcZskZbsd9sNyePcfeVaP4LOngwAbTIC83XAxZ0tD9OLeeABRkDku2fuk0g+y1 vstwxk+/WhMNWC4TKaJKBgVr2tlhJXr8haGlDj+OOWbpwHcqLVLpM2JSWcocgfM36d HLmybkPMy9ZN7sn4pjH3nT3ZPU7em7QOZfiDKF4RONrF1zS36XPL5OKSnUO/ssNOeC pS+ILw0MfO9dd3fEWa2rCS0SnBmB2tQspRAuCzajsGzLB4XsyHpeL5xuk7z/UfLkn2 7SuletPW9yxvfC/foN7weNDFmUfGCQLHJqaM3/IweckoYiTFcZQvuwWN4OMOOGd+bN Hfz2vMMkXxzaA== Message-ID: Date: Wed, 10 Jun 2026 15:18:52 +0200 Precedence: bulk X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC v1] io_uring/rsrc: add fast path huge page handling in buffer registration To: Christoph Hellwig Cc: sw.prabhu6@gmail.com, axboe@kernel.dk, io-uring@vger.kernel.org, linux-kernel@vger.kernel.org, dave@stgolabs.net, dongjoo.seo1@samsung.com, Swarna Prabhu , "linux-mm@kvack.org" , Matthew Wilcox , Zi Yan References: <20260608062937.804758-1-sw.prabhu6@gmail.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 6/10/26 13:34, Christoph Hellwig wrote: > On Wed, Jun 10, 2026 at 11:54:01AM +0200, David Hildenbrand (Arm) wrote: >>> Yes. iov_iter_extract_bvecs and thus the block direct I/O fast path >>> would instantly benefit from that. >> The tricky bit for such an interface is that, soon, some pages won't be folios, >> but we could still end up with non-folio pages in the address space (e.g., >> vm_insert_page()) and have to pin+return them. So using folios is not future-proof. > > I'm still doubtful on the "soon" beause of all the issues like this > in the I/O path. Yeah, there are a bunch of very hairy things. > >> There are some long-term plans on providing an interface that would abstract how >> you refcount something you GUP'ed. (because, some pages we GUP in the future >> might not even have a dedicated refcount, all still fairly unclear). But it's >> all not really finalized I think. >> >> For now, we could expose a folio+page/offset+nr_pages interface, where we, >> long-term, would not be able to return non-folio pages (e.g., vm_insert_page()) >> and would instead, in the future, fail the request if we stumble over a >> non-folio thing in the page tables. That sounds reasonable for now. > > I think whatever we're going to use for direct I/O has to also support > non-folio pages, especially PCI P2P memory. So coming up with an > interface that support this ASAP would be helpful. Yes. I think we can keep returning pages as long a the unpin interface knows the right thing to do to unpin them. > >> Another solution would be, exposing page-ranges (e.g., page + nr_pages), whereby >> we'd say, that all pages in a range belong to the same compound page, and that >> we took a single reference for all pages in the range. IOW, page_folio() would >> for now be the same for all pages in a range. > > This does sound like a reasonable short-term improvement. Right, and as long as callers don't cast the returned thing to a folio, it would be future proof. But I guess quite some GUP users cast to folios. Would there be users for a new interface that returns page ranges as described above, that would want to still unpin stuff partially? E.g., we give them a page range that belongs to the same folio with only a single pin/reference, but they would want to logically split that range and unpin pages individually? -- Cheers, David