From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yk0-f181.google.com (mail-yk0-f181.google.com [209.85.160.181]) by kanga.kvack.org (Postfix) with ESMTP id 9FDAB828F3 for ; Sun, 10 Jan 2016 20:19:06 -0500 (EST) Received: by mail-yk0-f181.google.com with SMTP id x67so417167189ykd.2 for ; Sun, 10 Jan 2016 17:19:06 -0800 (PST) Received: from mail-yk0-x232.google.com (mail-yk0-x232.google.com. [2607:f8b0:4002:c07::232]) by mx.google.com with ESMTPS id q185si14783320ywe.315.2016.01.10.17.19.05 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 10 Jan 2016 17:19:05 -0800 (PST) Received: by mail-yk0-x232.google.com with SMTP id v14so323049291ykd.3 for ; Sun, 10 Jan 2016 17:19:05 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <569263BA.5060503@plexistor.com> References: <569263BA.5060503@plexistor.com> Date: Sun, 10 Jan 2016 17:19:05 -0800 Message-ID: Subject: Re: [PATCHSET 0/2] Allow single pagefault in write access of a VM_MIXEDMAP mapping From: Dan Williams Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Boaz Harrosh Cc: "Kirill A. Shutemov" , Andrew Morton , Matthew Wilcox , "linux-mm@kvack.org" , Ross Zwisler , Oleg Nesterov , Mel Gorman , Johannes Weiner On Sun, Jan 10, 2016 at 5:59 AM, Boaz Harrosh wrote: > Hi > > Today any VM_MIXEDMAP or VM_PFN mapping when enabling a write access > to their mapping, will have a double pagefault for every write access. > > This is because vma->vm_page_prot defines how a page/pfn is inserted into > the page table (see vma_wants_writenotify in mm/mmap.c). > > Which means that it is always inserted with read-only under the > assumption that we want to be notified when write access occurs. > > But this is not always true and adds an unnecessary page-fault on > every new mmap-write access > > This patchset is trying to give the fault handler more choice by passing > an pgprot_t to vm_insert_mixed() via a new vm_insert_mixed_prot() API. > > If the mm guys feel that the pgprot_t and its helpers and flags are private > to mm/memory.c I can easily do a new: vm_insert_mixed_rw() instead. of the > above vm_insert_mixed_prot() which enables any control not only write. > > Following is a patch to DAX to optimize out the extra page-fault. > > TODO: I only did 4k mapping perhaps 2M mapping can enjoy the same single > fault on write access. If interesting to anyone I can attempt a fix. > > Dan Andrew who needs to pick this up please? This collides with the patches currently pending in -mm for 4.5, lets take a look at this for 4.6. -- 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