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[70.52.229.124]) by smtp.gmail.com with ESMTPSA id y19-20020a05622a121300b003e390b48958sm2613867qtx.55.2023.04.26.07.13.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 26 Apr 2023 07:13:29 -0700 (PDT) Date: Wed, 26 Apr 2023 10:13:27 -0400 From: Peter Xu To: Muhammad Usama Anjum Cc: Paul Gofman , Alexander Viro , Shuah Khan , Christian Brauner , Yang Shi , Vlastimil Babka , "Liam R . Howlett" , Yun Zhou , Cyrill Gorcunov , =?utf-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= , Andrew Morton , Suren Baghdasaryan , Andrei Vagin , Alex Sierra , Matthew Wilcox , Pasha Tatashin , Danylo Mocherniuk , Axel Rasmussen , "Gustavo A . R . Silva" , David Hildenbrand , Dan Williams , linux-kernel@vger.kernel.org, Mike Rapoport , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, Greg KH , kernel@collabora.com, Nadav Amit Subject: Re: [PATCH RESEND v15 2/5] fs/proc/task_mmu: Implement IOCTL to get and optionally clear info about PTEs Message-ID: References: <20230420060156.895881-1-usama.anjum@collabora.com> <20230420060156.895881-3-usama.anjum@collabora.com> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: C2FCF1C0012 X-Stat-Signature: 8un53wpyyokdjjrtotipds3edobizte6 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1682518414-602663 X-HE-Meta: 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 /b9T5JiC eCdmTXzA+XBzYaw+TnR85TDKAfepPOq3ni+iKIwTQj99Z9bLwWYDtTk5t6anfExralNHvJ3zzRbjf5gkluw8jmsNTfg7jLiV2TEF8m+TewYq31rTZdxvdzidZAM8kBx/L1mvjVdSHnWNz7yr0MfIg0rqz4zdypt2GVrGbKgoysWn/hsJLeJAY26jtv70l/I54k2aNPeNaSiADa9fosNJlNgooeR4OmYJ6/+fX2Kk1kRPfDWJt0MZOktPf9XRLmievuDFegj/FVXq2ms/JkdtfWDiRn5rbaIsvGYh7FucE9AWD+ax2VX1GNo97t+N8BE36BOSrYkiFT8SaGRE7aNyFgYBlyTtgPYpjt5EDsFMmpjm2d5zLKuqlbjBSGJJboAXxSiq7UChK1aIvvl1dbg1/eeOeyPKa1qcqVFcy 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: Hi, Muhammad, On Wed, Apr 26, 2023 at 12:06:23PM +0500, Muhammad Usama Anjum wrote: > On 4/20/23 11:01 AM, Muhammad Usama Anjum wrote: > > +/* Supported flags */ > > +#define PM_SCAN_OP_GET (1 << 0) > > +#define PM_SCAN_OP_WP (1 << 1) > We have only these flag options available in PAGEMAP_SCAN IOCTL. > PM_SCAN_OP_GET must always be specified for this IOCTL. PM_SCAN_OP_WP can > be specified as need. But PM_SCAN_OP_WP cannot be specified without > PM_SCAN_OP_GET. (This was removed after you had asked me to not duplicate > functionality which can be achieved by UFFDIO_WRITEPROTECT.) > > 1) PM_SCAN_OP_GET | PM_SCAN_OP_WP > vs > 2) UFFDIO_WRITEPROTECT > > After removing the usage of uffd_wp_range() from PAGEMAP_SCAN IOCTL, we are > getting really good performance which is comparable just like we are > depending on SOFT_DIRTY flags in the PTE. But when we want to perform wp, > PM_SCAN_OP_GET | PM_SCAN_OP_WP is more desirable than UFFDIO_WRITEPROTECT > performance and behavior wise. > > I've got the results from someone else that UFFDIO_WRITEPROTECT block > pagefaults somehow which PAGEMAP_IOCTL doesn't. I still need to verify this > as I don't have tests comparing them one-to-one. > > What are your thoughts about it? Have you thought about making > UFFDIO_WRITEPROTECT perform better? > > I'm sorry to mention the word "performance" here. Actually we want better > performance to emulate Windows syscall. That is why we are adding this > functionality. So either we need to see what can be improved in > UFFDIO_WRITEPROTECT or can I please add only PM_SCAN_OP_WP back in > pagemap_ioctl? I'm fine if you want to add it back if it works for you. Though before that, could you remind me why there can be a difference on performance? Thanks, -- Peter Xu