From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f69.google.com (mail-pg0-f69.google.com [74.125.83.69]) by kanga.kvack.org (Postfix) with ESMTP id 460DA6B0033 for ; Fri, 24 Nov 2017 10:43:25 -0500 (EST) Received: by mail-pg0-f69.google.com with SMTP id j16so22221719pgn.14 for ; Fri, 24 Nov 2017 07:43:25 -0800 (PST) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id r26si20255859pfi.232.2017.11.24.07.43.23 for (version=TLS1 cipher=AES128-SHA bits=128/128); Fri, 24 Nov 2017 07:43:23 -0800 (PST) Date: Fri, 24 Nov 2017 16:43:17 +0100 From: Michal Hocko Subject: Re: [PATCH v2 2/5] mm: memory_hotplug: Remove assumption on memory state before hotremove Message-ID: <20171124154317.copbe3u6y2q4mura@dhcp22.suse.cz> References: <4e21a27570f665793debf167c8567c6752116d0a.1511433386.git.ar@linux.vnet.ibm.com> <20171124144917.GB1966@samekh> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171124144917.GB1966@samekh> Sender: owner-linux-mm@kvack.org List-ID: To: Andrea Reale Cc: "Rafael J. Wysocki" , "linux-arm-kernel@lists.infradead.org" , Linux Kernel Mailing List , Linux Memory Management List , m.bielski@virtualopensystems.com, arunks@qti.qualcomm.com, Mark Rutland , scott.branden@broadcom.com, Will Deacon , qiuxishi@huawei.com, Catalin Marinas , Rafael Wysocki , ACPI Devel Maling List On Fri 24-11-17 14:49:17, Andrea Reale wrote: > Hi Rafael, > > On Fri 24 Nov 2017, 15:39, Rafael J. Wysocki wrote: > > On Fri, Nov 24, 2017 at 11:22 AM, Andrea Reale wrote: > > > Resending the patch adding linux-acpi in CC, as suggested by Rafael. > > > Everyone else: apologies for the noise. > > > > > > Commit 242831eb15a0 ("Memory hotplug / ACPI: Simplify memory removal") > > > introduced an assumption whereas when control > > > reaches remove_memory the corresponding memory has been already > > > offlined. In that case, the acpi_memhotplug was making sure that > > > the assumption held. > > > This assumption, however, is not necessarily true if offlining > > > and removal are not done by the same "controller" (for example, > > > when first offlining via sysfs). > > > > > > Removing this assumption for the generic remove_memory code > > > and moving it in the specific acpi_memhotplug code. This is > > > a dependency for the software-aided arm64 offlining and removal > > > process. > > > > > > Signed-off-by: Andrea Reale > > > Signed-off-by: Maciej Bielski > > > --- > > > drivers/acpi/acpi_memhotplug.c | 2 +- > > > include/linux/memory_hotplug.h | 9 ++++++--- > > > mm/memory_hotplug.c | 13 +++++++++---- > > > 3 files changed, 16 insertions(+), 8 deletions(-) > > > > > > diff --git a/drivers/acpi/acpi_memhotplug.c b/drivers/acpi/acpi_memhotplug.c > > > index 6b0d3ef..b0126a0 100644 > > > --- a/drivers/acpi/acpi_memhotplug.c > > > +++ b/drivers/acpi/acpi_memhotplug.c > > > @@ -282,7 +282,7 @@ static void acpi_memory_remove_memory(struct acpi_memory_device *mem_device) > > > nid = memory_add_physaddr_to_nid(info->start_addr); > > > > > > acpi_unbind_memory_blocks(info); > > > - remove_memory(nid, info->start_addr, info->length); > > > + BUG_ON(remove_memory(nid, info->start_addr, info->length)); > > > > Why does this have to be BUG_ON()? Is it really necessary to kill the > > system here? > > Actually, I hoped you would help me understand that: that BUG() call was introduced > by yourself in Commit 242831eb15a0 ("Memory hotplug / ACPI: Simplify memory removal") > in memory_hoptlug.c:remove_memory()). > > Just reading at that commit my understanding was that you were assuming > that acpi_memory_remove_memory() have already done the job of offlining > the target memory, so there would be a bug if that wasn't the case. > > In my case, that assumption did not hold and I found that it might not > hold for other platforms that do not use ACPI. In fact, the purpose of > this patch is to move this assumption out of the generic hotplug code > and move it to ACPI code where it originated. remove_memory failure is basically impossible to handle AFAIR. The original code to BUG in remove_memory is ugly as hell and we do not want to spread that out of that function. Instead we really want to get rid of it. -- Michal Hocko SUSE Labs -- 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