From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg1-f199.google.com (mail-pg1-f199.google.com [209.85.215.199]) by kanga.kvack.org (Postfix) with ESMTP id 086C56B0006 for ; Thu, 11 Oct 2018 19:22:33 -0400 (EDT) Received: by mail-pg1-f199.google.com with SMTP id t3-v6so7750610pgp.0 for ; Thu, 11 Oct 2018 16:22:33 -0700 (PDT) Received: from mga02.intel.com (mga02.intel.com. [134.134.136.20]) by mx.google.com with ESMTPS id q1-v6si4290987pls.17.2018.10.11.16.22.31 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 11 Oct 2018 16:22:31 -0700 (PDT) Subject: Re: [mm PATCH v2 4/6] mm: Do not set reserved flag for hotplug memory References: <20181011221237.1925.85591.stgit@localhost.localdomain> <20181011221351.1925.67694.stgit@localhost.localdomain> From: Alexander Duyck Message-ID: <0b7001f8-3653-d100-4218-3d9b06ff8b3a@linux.intel.com> Date: Thu, 11 Oct 2018 16:22:30 -0700 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Dan Williams Cc: Linux MM , Andrew Morton , Pasha Tatashin , Michal Hocko , Dave Jiang , Linux Kernel Mailing List , Matthew Wilcox , David Miller , Zhang Yi , khalid.aziz@oracle.com, rppt@linux.vnet.ibm.com, Vlastimil Babka , sparclinux@vger.kernel.org, Laurent Dufour , Mel Gorman , Ingo Molnar , "Kirill A. Shutemov" On 10/11/2018 3:58 PM, Dan Williams wrote: > On Thu, Oct 11, 2018 at 3:18 PM Alexander Duyck > wrote: >> >> The general suspicion at this point is that the setting of the reserved bit >> is not really needed for hotplug memory. In addition the setting of this >> bit results in issues for DAX in that it is not possible to assign the >> region to KVM if the reserved bit is set in each page. >> >> For now we can try just not setting the bit since we suspect it isn't >> adding value in setting it. If at a later time we find that it is needed we >> can come back through and re-add it for the hotplug paths. >> >> Suggested-by: Michael Hocko >> Reported-by: Dan Williams >> Signed-off-by: Alexander Duyck >> --- >> mm/page_alloc.c | 11 ----------- >> 1 file changed, 11 deletions(-) >> >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >> index 3603d5444865..e435223e2ddb 100644 >> --- a/mm/page_alloc.c >> +++ b/mm/page_alloc.c >> @@ -5571,8 +5571,6 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone, >> >> page = pfn_to_page(pfn); >> __init_single_page(page, pfn, zone, nid); >> - if (context == MEMMAP_HOTPLUG) >> - __SetPageReserved(page); > > At a minimum I think we need to do this before removing PageReserved, > to make sure zone_device pages are not tracked in the hibernation > image. > > diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c > index 3d37c279c090..c0613137d726 100644 > --- a/kernel/power/snapshot.c > +++ b/kernel/power/snapshot.c > @@ -1285,6 +1285,9 @@ static struct page *saveable_page(struct zone > *zone, unsigned long pfn) > if (swsusp_page_is_forbidden(page) || swsusp_page_is_free(page)) > return NULL; > > + if (is_zone_device_page(page)) > + return NULL; > + > if (PageReserved(page) > && (!kernel_page_present(page) || pfn_is_nosave(pfn))) > return NULL; > Yeah, I am pretty sure I broke hotplug in general with this too since it seems like it checks for the reserved flag before bringing a range online in online_pages_range. I think I will drop this patch and go back to what I had before. There was a slight performance gain to be had for not setting the bit at all, but I think we are probably looking at yet another patch set if we want to go through and drop the need for the reserved bit to be set. - Alex