From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrea Arcangeli Subject: Re: [PATCH 14/23] userfaultfd: wake pending userfaults Date: Thu, 22 Oct 2015 17:30:55 +0200 Message-ID: <20151022153055.GC1331@redhat.com> References: <1431624680-20153-1-git-send-email-aarcange@redhat.com> <1431624680-20153-15-git-send-email-aarcange@redhat.com> <20151022121056.GB7520@twins.programming.kicks-ass.net> <20151022132015.GF19147@redhat.com> <20151022133824.GR17308@twins.programming.kicks-ass.net> <20151022141831.GA1331@redhat.com> <20151022151509.GO3604@twins.programming.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20151022151509.GO3604@twins.programming.kicks-ass.net> Sender: owner-linux-mm@kvack.org To: Peter Zijlstra Cc: Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, qemu-devel@nongnu.org, kvm@vger.kernel.org, linux-api@vger.kernel.org, Pavel Emelyanov , Sanidhya Kashyap , zhang.zhanghailiang@huawei.com, Linus Torvalds , "Kirill A. Shutemov" , Andres Lagar-Cavilla , Dave Hansen , Paolo Bonzini , Rik van Riel , Mel Gorman , Andy Lutomirski , Hugh Dickins , Peter Feiner , "Dr. David Alan Gilbert" , Johannes Weiner , "Huangpeng (Peter)" List-Id: linux-api@vger.kernel.org On Thu, Oct 22, 2015 at 05:15:09PM +0200, Peter Zijlstra wrote: > Indefinitely is such a long time, we should try and finish > computation before the computer dies etc. :-) Indefinitely as read_seqcount_retry, eventually it makes progress. Even returning 0 from the page fault can trigger it again indefinitely, so VM_FAULT_RETRY isn't fundamentally different from returning 0 and retrying the page fault again later. So it's not clear why VM_FAULT_RETRY can only try once more. FAULT_FLAG_TRIED as a message to the VM so it starts to do heavy locking and block more aggressively is actually useful as such, but it shouldn't be a replacement of FAULT_FLAG_ALLOW_RETRY. What I meant with removing FAULT_FLAG_TRIED is really about converting it to an hint, but not controlling if the page fault can keep retrying in-kernel. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org