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[174.93.89.182]) by smtp.gmail.com with ESMTPSA id f188sm7216631qkj.110.2021.02.12.14.44.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 12 Feb 2021 14:44:07 -0800 (PST) Date: Fri, 12 Feb 2021 17:44:05 -0500 From: Peter Xu To: Matthew Wilcox Cc: Axel Rasmussen , Alexander Viro , Alexey Dobriyan , Andrea Arcangeli , Andrew Morton , Anshuman Khandual , Catalin Marinas , Chinwen Chang , Huang Ying , Ingo Molnar , Jann Horn , Jerome Glisse , Lokesh Gidra , Michael Ellerman , Michal =?utf-8?Q?Koutn=C3=BD?= , Michel Lespinasse , Mike Kravetz , Mike Rapoport , Nicholas Piggin , Shaohua Li , Shawn Anastasio , Steven Rostedt , Steven Price , Vlastimil Babka , LKML , linux-fsdevel@vger.kernel.org, Linux MM , Adam Ruprecht , Cannon Matthews , "Dr . David Alan Gilbert" , David Rientjes , Mina Almasry , Oliver Upton Subject: Re: [PATCH v5 05/10] userfaultfd: add minor fault registration mode Message-ID: <20210212224405.GF3171@xz-x1> References: <20210210212200.1097784-1-axelrasmussen@google.com> <20210210212200.1097784-6-axelrasmussen@google.com> <20210212222145.GB2858050@casper.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20210212222145.GB2858050@casper.infradead.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 12, 2021 at 10:21:45PM +0000, Matthew Wilcox wrote: > On Thu, Feb 11, 2021 at 11:28:09AM -0800, Axel Rasmussen wrote: > > Ah, I had added this just after VM_UFFD_WP, without noticing that this > > would be sharing a bit with VM_LOCKED. That seems like not such a > > great idea. > > > > I don't see another unused bit, and I don't see some other obvious > > candidate to share with. So, the solution that comes to mind is > > it'd be even better if you didn't use the last unused bit for UFFD_WP. > not sure how feasible that is, but you can see we're really short on > bits here. UFFD_WP is used now for anonymouse already.. And the support for hugetlbfs and shmem is in rfc stage on the list. Is it possible to use CONFIG_ARCH_USES_HIGH_VMA_FLAGS here? So far uffd-wp is only working for 64 bit x86 too due to enlarged pte space. Maybe we can also let minor mode to only support 64 bit hosts. Thanks, -- Peter Xu