From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl1-f199.google.com (mail-pl1-f199.google.com [209.85.214.199]) by kanga.kvack.org (Postfix) with ESMTP id C31796B0003 for ; Wed, 10 Oct 2018 22:29:35 -0400 (EDT) Received: by mail-pl1-f199.google.com with SMTP id d40-v6so5247272pla.14 for ; Wed, 10 Oct 2018 19:29:35 -0700 (PDT) Received: from smtp.codeaurora.org (smtp.codeaurora.org. [198.145.29.96]) by mx.google.com with ESMTPS id l12-v6si25463057pgj.76.2018.10.10.19.29.33 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 10 Oct 2018 19:29:34 -0700 (PDT) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Thu, 11 Oct 2018 07:59:32 +0530 From: Arun KS Subject: Re: [PATCH v5 1/2] memory_hotplug: Free pages as higher order In-Reply-To: <20181010173334.GL5873@dhcp22.suse.cz> References: <1538727006-5727-1-git-send-email-arunks@codeaurora.org> <72215e75-6c7e-0aef-c06e-e3aba47cf806@suse.cz> <20181010173334.GL5873@dhcp22.suse.cz> Message-ID: Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Vlastimil Babka , kys@microsoft.com, haiyangz@microsoft.com, sthemmin@microsoft.com, boris.ostrovsky@oracle.com, jgross@suse.com, akpm@linux-foundation.org, dan.j.williams@intel.com, iamjoonsoo.kim@lge.com, gregkh@linuxfoundation.org, osalvador@suse.de, malat@debian.org, kirill.shutemov@linux.intel.com, jrdr.linux@gmail.com, yasu.isimatu@gmail.com, mgorman@techsingularity.net, aaron.lu@intel.com, devel@linuxdriverproject.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, xen-devel@lists.xenproject.org, vatsa@codeaurora.org, vinmenon@codeaurora.org, getarunks@gmail.com On 2018-10-10 23:03, Michal Hocko wrote: > On Wed 10-10-18 22:26:41, Arun KS wrote: >> On 2018-10-10 21:00, Vlastimil Babka wrote: >> > On 10/5/18 10:10 AM, Arun KS wrote: >> > > When free pages are done with higher order, time spend on >> > > coalescing pages by buddy allocator can be reduced. With >> > > section size of 256MB, hot add latency of a single section >> > > shows improvement from 50-60 ms to less than 1 ms, hence >> > > improving the hot add latency by 60%. Modify external >> > > providers of online callback to align with the change. >> > > >> > > Signed-off-by: Arun KS >> > >> > [...] >> > >> > > @@ -655,26 +655,44 @@ void __online_page_free(struct page *page) >> > > } >> > > EXPORT_SYMBOL_GPL(__online_page_free); >> > > >> > > -static void generic_online_page(struct page *page) >> > > +static int generic_online_page(struct page *page, unsigned int order) >> > > { >> > > - __online_page_set_limits(page); >> > >> > This is now not called anymore, although the xen/hv variants still do >> > it. The function seems empty these days, maybe remove it as a followup >> > cleanup? >> > >> > > - __online_page_increment_counters(page); >> > > - __online_page_free(page); >> > > + __free_pages_core(page, order); >> > > + totalram_pages += (1UL << order); >> > > +#ifdef CONFIG_HIGHMEM >> > > + if (PageHighMem(page)) >> > > + totalhigh_pages += (1UL << order); >> > > +#endif >> > >> > __online_page_increment_counters() would have used >> > adjust_managed_page_count() which would do the changes under >> > managed_page_count_lock. Are we safe without the lock? If yes, there >> > should perhaps be a comment explaining why. >> >> Looks unsafe without managed_page_count_lock. > > Why does it matter actually? We cannot online/offline memory in > parallel. This is not the case for the boot where we initialize memory > in parallel on multiple nodes. So this seems to be safe currently > unless > I am missing something. A comment explaining that would be helpful > though. Other main callers of adjust_manage_page_count(), static inline void free_reserved_page(struct page *page) { __free_reserved_page(page); adjust_managed_page_count(page, 1); } static inline void mark_page_reserved(struct page *page) { SetPageReserved(page); adjust_managed_page_count(page, -1); } Won't they race with memory hotplug? Few more, ./drivers/xen/balloon.c:519: adjust_managed_page_count(page, -1); ./drivers/virtio/virtio_balloon.c:175: adjust_managed_page_count(page, -1); ./drivers/virtio/virtio_balloon.c:196: adjust_managed_page_count(page, 1); ./mm/hugetlb.c:2158: adjust_managed_page_count(page, 1 << h->order); Regards, Arun