From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-it0-f71.google.com (mail-it0-f71.google.com [209.85.214.71]) by kanga.kvack.org (Postfix) with ESMTP id B04A76B02E1 for ; Fri, 28 Apr 2017 15:02:41 -0400 (EDT) Received: by mail-it0-f71.google.com with SMTP id o128so29385579itg.18 for ; Fri, 28 Apr 2017 12:02:41 -0700 (PDT) Received: from mail-io0-x22a.google.com (mail-io0-x22a.google.com. [2607:f8b0:4001:c06::22a]) by mx.google.com with ESMTPS id d22si7944472iof.230.2017.04.28.12.02.40 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 28 Apr 2017 12:02:40 -0700 (PDT) Received: by mail-io0-x22a.google.com with SMTP id k87so74651485ioi.0 for ; Fri, 28 Apr 2017 12:02:40 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <1579714997.4315035.1493402406629.JavaMail.zimbra@redhat.com> References: <20170428063913.iz6xjcxblecofjlq@gmail.com> <149339998297.24933.1129582806028305912.stgit@dwillia2-desk3.amr.corp.intel.com> <1743017574.4309811.1493400875692.JavaMail.zimbra@redhat.com> <1579714997.4315035.1493402406629.JavaMail.zimbra@redhat.com> From: Dan Williams Date: Fri, 28 Apr 2017 12:02:39 -0700 Message-ID: Subject: Re: [PATCH v2] mm, zone_device: replace {get, put}_zone_device_page() with a single reference Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Jerome Glisse Cc: Ingo Molnar , "linux-kernel@vger.kernel.org" , Linux MM , Ingo Molnar , Andrew Morton , Logan Gunthorpe , Kirill Shutemov On Fri, Apr 28, 2017 at 11:00 AM, Jerome Glisse wrote: >> On Fri, Apr 28, 2017 at 10:34 AM, Jerome Glisse wrote: >> >> Kirill points out that the calls to {get,put}_dev_pagemap() can be >> >> removed from the mm fast path if we take a single get_dev_pagemap() >> >> reference to signify that the page is alive and use the final put of the >> >> page to drop that reference. >> >> >> >> This does require some care to make sure that any waits for the >> >> percpu_ref to drop to zero occur *after* devm_memremap_page_release(), >> >> since it now maintains its own elevated reference. >> > >> > This is NAK from HMM point of view as i need those call. So if you remove >> > them now i will need to add them back as part of HMM. >> >> I thought you only need them at page free time? You can still hook >> __put_page(). > > No, i need a hook when page refcount reach 1, not 0. That being said > i don't care about put_dev_pagemap(page->pgmap); so that part of the > patch is fine from HMM point of view but i definitly need to hook my- > self in the general put_page() function. > > So i will have to undo part of this patch for HMM (put_page() will > need to handle ZONE_DEVICE page differently). Ok, I'd rather this go in now since it fixes the existing use case, and unblocks the get_user_pages_fast() conversion to generic code. That also gives Kirill and -mm folks a chance to review what HMM wants to do on top of the page_ref infrastructure. The {get,put}_zone_device_page interface went in in 4.5 right before page_ref went in during 4.6, so it was just an oversight that {get,put}_zone_device_page were not removed earlier. -- 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