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Fri, 23 Sep 2022 17:01:35 -0600 Message-ID: <3840c1c6-3a5c-2286-e577-949f0d4ea7a6@deltatee.com> Date: Fri, 23 Sep 2022 17:01:26 -0600 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.13.0 Content-Language: en-CA To: Jason Gunthorpe Cc: linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, linux-block@vger.kernel.org, linux-pci@vger.kernel.org, linux-mm@kvack.org, Christoph Hellwig , Greg Kroah-Hartman , Dan Williams , =?UTF-8?Q?Christian_K=c3=b6nig?= , John Hubbard , Don Dutile , Matthew Wilcox , Daniel Vetter , Minturn Dave B , Jason Ekstrand , Dave Hansen , Xiong Jianxin , Bjorn Helgaas , Ira Weiny , Robin Murphy , Martin Oliveira , Chaitanya Kulkarni , Ralph Campbell , Stephen Bates References: <20220922163926.7077-1-logang@deltatee.com> <20220922163926.7077-2-logang@deltatee.com> <64f8da81-7803-4db4-73da-a158295cbc9c@deltatee.com> <2327d393-af5c-3f4c-b9b9-6852b9d72f90@deltatee.com> From: Logan Gunthorpe In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 24.64.144.200 X-SA-Exim-Rcpt-To: jgg@ziepe.ca, linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, linux-block@vger.kernel.org, linux-pci@vger.kernel.org, linux-mm@kvack.org, hch@lst.de, gregkh@linuxfoundation.org, dan.j.williams@intel.com, christian.koenig@amd.com, jhubbard@nvidia.com, ddutile@redhat.com, willy@infradead.org, daniel.vetter@ffwll.ch, dave.b.minturn@intel.com, jason@jlekstrand.net, dave.hansen@linux.intel.com, jianxin.xiong@intel.com, helgaas@kernel.org, ira.weiny@intel.com, robin.murphy@arm.com, martin.oliveira@eideticom.com, ckulkarnilinux@gmail.com, rcampbell@nvidia.com, sbates@raithlin.com X-SA-Exim-Mail-From: logang@deltatee.com Subject: Re: [PATCH v10 1/8] mm: introduce FOLL_PCI_P2PDMA to gate getting PCI P2PDMA pages X-SA-Exim-Version: 4.2.1 (built Sat, 13 Feb 2021 17:57:42 +0000) X-SA-Exim-Scanned: Yes (on ale.deltatee.com) ARC-Authentication-Results: i=1; imf12.hostedemail.com; dkim=pass header.d=deltatee.com header.s=20200525 header.b=CGuPbm2G; 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dkim=pass header.d=deltatee.com header.s=20200525 header.b=CGuPbm2G; spf=pass (imf12.hostedemail.com: domain of logang@deltatee.com designates 204.191.154.188 as permitted sender) smtp.mailfrom=logang@deltatee.com; dmarc=pass (policy=none) header.from=deltatee.com X-Rspam-User: X-Rspamd-Server: rspam05 X-HE-Tag: 1663974102-71573 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: On 2022-09-23 16:58, Jason Gunthorpe wrote: > On Fri, Sep 23, 2022 at 02:11:03PM -0600, Logan Gunthorpe wrote: >> >> >> On 2022-09-23 13:53, Jason Gunthorpe wrote: >>> On Fri, Sep 23, 2022 at 01:08:31PM -0600, Logan Gunthorpe wrote: >>> I'm encouraging Dan to work on better infrastructure in pgmap core >>> because every pgmap implementation has this issue currently. >>> >>> For that reason it is probably not so relavent to this series. >>> >>> Perhaps just clarify in the commit message that the FOLL_LONGTERM >>> restriction is to copy DAX until the pgmap page refcounts are fixed. >> >> Ok, I'll add that note. >> >> Per the fix for the try_grab_page(), to me it doesn't fit well in >> try_grab_page() without doing a bunch of cleanup to change the >> error handling, and the same would have to be added to try_grab_folio(). >> So I think it's better to leave it where it was, but move it below the >> respective grab calls. Does the incremental patch below look correct? > > Oh? I was thinking of just a very simple thing: Really would like it to return -EREMOTEIO instead of -ENOMEM as that's the error used for bad P2PDMA page everywhere. Plus the concern that some of the callsites of try_grab_page() might not have a get or a pin and thus it's not safe which was the whole point of the change anyway. Plus we have to do the same for try_grab_folio(). Logan