From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id AC7B9C49ED7 for ; Tue, 17 Sep 2019 03:09:56 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 7A0C3206A1 for ; Tue, 17 Sep 2019 03:09:56 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7A0C3206A1 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 11AED6B0003; Mon, 16 Sep 2019 23:09:56 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 0CD1A6B0005; Mon, 16 Sep 2019 23:09:56 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id EFCCF6B0006; Mon, 16 Sep 2019 23:09:55 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0069.hostedemail.com [216.40.44.69]) by kanga.kvack.org (Postfix) with ESMTP id D134C6B0003 for ; Mon, 16 Sep 2019 23:09:55 -0400 (EDT) Received: from smtpin14.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with SMTP id 5894B180AD802 for ; Tue, 17 Sep 2019 03:09:55 +0000 (UTC) X-FDA: 75942933150.14.drink17_7367016a2d356 X-HE-Tag: drink17_7367016a2d356 X-Filterd-Recvd-Size: 4795 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf48.hostedemail.com (Postfix) with ESMTP for ; Tue, 17 Sep 2019 03:09:52 +0000 (UTC) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 02989337; Mon, 16 Sep 2019 20:09:52 -0700 (PDT) Received: from [10.162.40.131] (p8cg001049571a15.blr.arm.com [10.162.40.131]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8E5E53F575; Mon, 16 Sep 2019 20:09:49 -0700 (PDT) Subject: Re: [PATCH] mm/hotplug: Reorder memblock_[free|remove]() calls in try_remove_memory() To: Mike Rapoport Cc: linux-mm@kvack.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, Oscar Salvador , Michal Hocko , David Hildenbrand , Pavel Tatashin , Dan Williams References: <1568612857-10395-1-git-send-email-anshuman.khandual@arm.com> <20190916063612.GA1502@linux.ibm.com> <987dfde7-53f9-b013-5841-2c27c03d62d6@arm.com> From: Anshuman Khandual Message-ID: Date: Tue, 17 Sep 2019 08:40:03 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <987dfde7-53f9-b013-5841-2c27c03d62d6@arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 09/16/2019 02:20 PM, Anshuman Khandual wrote: > > > On 09/16/2019 12:06 PM, Mike Rapoport wrote: >> On Mon, Sep 16, 2019 at 11:17:37AM +0530, Anshuman Khandual wrote: >>> In add_memory_resource() the memory range to be hot added first gets into >>> the memblock via memblock_add() before arch_add_memory() is called on it. >>> Reverse sequence should be followed during memory hot removal which already >>> is being followed in add_memory_resource() error path. This now ensures >>> required re-order between memblock_[free|remove]() and arch_remove_memory() >>> during memory hot-remove. >>> >>> Cc: Andrew Morton >>> Cc: Oscar Salvador >>> Cc: Michal Hocko >>> Cc: David Hildenbrand >>> Cc: Pavel Tatashin >>> Cc: Dan Williams >>> Signed-off-by: Anshuman Khandual >>> --- >>> Original patch https://lkml.org/lkml/2019/9/3/327 >>> >>> Memory hot remove now works on arm64 without this because a recent commit >>> 60bb462fc7ad ("drivers/base/node.c: simplify unregister_memory_block_under_nodes()"). >>> >>> David mentioned that re-ordering should still make sense for consistency >>> purpose (removing stuff in the reverse order they were added). This patch >>> is now detached from arm64 hot-remove series. >>> >>> https://lkml.org/lkml/2019/9/3/326 >>> >>> mm/memory_hotplug.c | 4 ++-- >>> 1 file changed, 2 insertions(+), 2 deletions(-) >>> >>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c >>> index c73f09913165..355c466e0621 100644 >>> --- a/mm/memory_hotplug.c >>> +++ b/mm/memory_hotplug.c >>> @@ -1770,13 +1770,13 @@ static int __ref try_remove_memory(int nid, u64 start, u64 size) >>> >>> /* remove memmap entry */ >>> firmware_map_remove(start, start + size, "System RAM"); >>> - memblock_free(start, size); >>> - memblock_remove(start, size); >>> >>> /* remove memory block devices before removing memory */ >>> remove_memory_block_devices(start, size); >>> >>> arch_remove_memory(nid, start, size, NULL); >>> + memblock_free(start, size); >> >> I don't see memblock_reserve() anywhere in memory_hotplug.c, so the >> memblock_free() call here seems superfluous. I think it can be simply >> dropped. > > I had observed that previously but was not sure whether or not there are > still scenarios where it might be true. Error path in add_memory_resource() > even just calls memblock_remove() not memblock_free(). Unless there is any > objection, can just drop it. Hello Mike, Looks like we might need memblock_free() here as well. As you mentioned before there might not be any memblock_reserve() in mm/memory_hotplug.c but that does not guarantee that there could not have been a previous memblock_reserve() or memblock_alloc_XXX() allocation which came from the current hot remove range. memblock_free() followed by memblock_remove() on the entire hot-remove range ensures that memblock.memory and memblock.reserve are in sync and the entire range is guaranteed to be removed from both the memory types. Or am I missing something here. - Anshuman