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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 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org 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