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McKenney" , Tim Chen , linuxppc-dev@lists.ozlabs.org, x86@kernel.org Subject: Re: [PATCH v12 00/31] Speculative page faults Message-ID: <20190423093851.GJ11158@hirez.programming.kicks-ass.net> References: <20190416134522.17540-1-ldufour@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) 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 Mon, Apr 22, 2019 at 02:29:16PM -0700, Michel Lespinasse wrote: > The proposed spf mechanism only handles anon vmas. Is there a > fundamental reason why it couldn't handle mapped files too ? > My understanding is that the mechanism of verifying the vma after > taking back the ptl at the end of the fault would work there too ? > The file has to stay referenced during the fault, but holding the vma's > refcount could be made to cover that ? the vm_file refcount would have > to be released in __free_vma() instead of remove_vma; I'm not quite sure > if that has more implications than I realize ? IIRC (and I really don't remember all that much) the trickiest bit was vs unmount. Since files can stay open past the 'expected' duration, umount could be delayed. But yes, I think I had a version that did all that just 'fine'. Like mentioned, I didn't keep the refcount because it sucked just as hard as the mmap_sem contention, but the SRCU callback did the fput() just fine (esp. now that we have delayed_fput).