From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 58D8FC433E1 for ; Wed, 8 Jul 2020 16:00:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 43A4620672 for ; Wed, 8 Jul 2020 16:00:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730592AbgGHQAn (ORCPT ); Wed, 8 Jul 2020 12:00:43 -0400 Received: from mx2.suse.de ([195.135.220.15]:36070 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730179AbgGHQAj (ORCPT ); Wed, 8 Jul 2020 12:00:39 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id BC203AE25; Wed, 8 Jul 2020 16:00:37 +0000 (UTC) Message-ID: Subject: Re: [PATCH] dma-pool: use single atomic pool for both DMA zones From: Nicolas Saenz Julienne To: Christoph Hellwig Cc: Marek Szyprowski , Robin Murphy , David Rientjes , linux-rpi-kernel@lists.infradead.org, jeremy.linton@arm.com, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org Date: Wed, 08 Jul 2020 18:00:35 +0200 In-Reply-To: <20200708153509.GA26743@lst.de> References: <20200707122804.21262-1-nsaenzjulienne@suse.de> <20200708153509.GA26743@lst.de> Content-Type: multipart/signed; micalg="pgp-sha256"; protocol="application/pgp-signature"; boundary="=-1l9N/1yPO/4ruj6aYldS" User-Agent: Evolution 3.36.3 MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --=-1l9N/1yPO/4ruj6aYldS Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, 2020-07-08 at 17:35 +0200, Christoph Hellwig wrote: > On Tue, Jul 07, 2020 at 02:28:04PM +0200, Nicolas Saenz Julienne wrote: > > When allocating atomic DMA memory for a device, the dma-pool core > > queries __dma_direct_optimal_gfp_mask() to check which atomic pool to > > use. It turns out the GFP flag returned is only an optimistic guess. > > The pool selected might sometimes live in a zone higher than the > > device's view of memory. > >=20 > > As there isn't a way to grantee a mapping between a device's DMA > > constraints and correct GFP flags this unifies both DMA atomic pools. > > The resulting pool is allocated in the lower DMA zone available, if any= , > > so as for devices to always get accessible memory while having the > > flexibility of using dma_pool_kernel for the non constrained ones. > >=20 > > Fixes: c84dc6e68a1d ("dma-pool: add additional coherent pools to map to= gfp > > mask") > > Reported-by: Jeremy Linton > > Suggested-by: Robin Murphy > > Signed-off-by: Nicolas Saenz Julienne >=20 > Hmm, this is not what I expected from the previous thread. I thought > we'd just use one dma pool based on runtime available of the zones.. I may be misunderstanding you, but isn't that going back to how things used= to be before pulling in David Rientjes' work? The benefit of having a GFP_KERN= EL pool is that non-address-constrained devices can get their atomic memory th= ere, instead of consuming somewhat scarcer low memory. --=-1l9N/1yPO/4ruj6aYldS Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- iQEzBAABCAAdFiEErOkkGDHCg2EbPcGjlfZmHno8x/4FAl8F7aMACgkQlfZmHno8 x/5/9gf+NzyxgUaobjh+kSJ+z1K3KcgSbBWTsleHIga7PNEsLskweeTIbHy8Mu+L +l3d5Luho/JiDNEwb/ogwIUOxxVnRMMypi0Pi1sSQKC8saaZBaACuZHlbl9FYola +hM7aLJNaSdqN5lEqo185qtvbWE4czz+Lvhw+AiuzzI4d4bKswtCYj9kKO70ir+I cTIIpzcwHXjDELCOGBnTmhIIL11feTP7BDZszZdk+Pp99KFBLPedpmSvp0PoaKN0 qxchAwBNrt31Jb1VjkMpRyAUqFZFPbcbBw0cqNdovej39bRIdJnjKUV2Qpg56ZRh S5MgcOa4ctQVFoo7VirwED00A3dGDg== =bCcC -----END PGP SIGNATURE----- --=-1l9N/1yPO/4ruj6aYldS--