From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:33838) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dmX5L-00044M-L9 for qemu-devel@nongnu.org; Mon, 28 Aug 2017 23:21:04 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dmX5H-0007Bx-LF for qemu-devel@nongnu.org; Mon, 28 Aug 2017 23:21:03 -0400 Received: from mga11.intel.com ([192.55.52.93]:7594) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dmX5H-0007AP-Bs for qemu-devel@nongnu.org; Mon, 28 Aug 2017 23:20:59 -0400 Message-ID: <59A4DE48.9030206@intel.com> Date: Tue, 29 Aug 2017 11:23:52 +0800 From: Wei Wang MIME-Version: 1.0 References: <1503914913-28893-1-git-send-email-wei.w.wang@intel.com> <1503914913-28893-5-git-send-email-wei.w.wang@intel.com> <20170828133326.GN17097@dhcp22.suse.cz> In-Reply-To: <20170828133326.GN17097@dhcp22.suse.cz> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v15 4/5] mm: support reporting free page blocks List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Michal Hocko Cc: virtio-dev@lists.oasis-open.org, linux-kernel@vger.kernel.org, qemu-devel@nongnu.org, virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, linux-mm@kvack.org, mst@redhat.com, akpm@linux-foundation.org, mawilcox@microsoft.com, david@redhat.com, cornelia.huck@de.ibm.com, mgorman@techsingularity.net, aarcange@redhat.com, amit.shah@redhat.com, pbonzini@redhat.com, willy@infradead.org, liliang.opensource@gmail.com, yang.zhang.wz@gmail.com, quan.xu@aliyun.com On 08/28/2017 09:33 PM, Michal Hocko wrote: > On Mon 28-08-17 18:08:32, Wei Wang wrote: >> This patch adds support to walk through the free page blocks in the >> system and report them via a callback function. Some page blocks may >> leave the free list after zone->lock is released, so it is the caller's >> responsibility to either detect or prevent the use of such pages. >> >> One use example of this patch is to accelerate live migration by skipping >> the transfer of free pages reported from the guest. A popular method used >> by the hypervisor to track which part of memory is written during live >> migration is to write-protect all the guest memory. So, those pages that >> are reported as free pages but are written after the report function >> returns will be captured by the hypervisor, and they will be added to the >> next round of memory transfer. > OK, looks much better. I still have few nits. > >> +extern void walk_free_mem_block(void *opaque, >> + int min_order, >> + bool (*report_page_block)(void *, unsigned long, >> + unsigned long)); >> + > please add names to arguments of the prototype > >> /* >> * Free reserved pages within range [PAGE_ALIGN(start), end & PAGE_MASK) >> * into the buddy system. The freed pages will be poisoned with pattern >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >> index 6d00f74..81eedc7 100644 >> --- a/mm/page_alloc.c >> +++ b/mm/page_alloc.c >> @@ -4762,6 +4762,71 @@ void show_free_areas(unsigned int filter, nodemask_t *nodemask) >> show_swap_cache_info(); >> } >> >> +/** >> + * walk_free_mem_block - Walk through the free page blocks in the system >> + * @opaque: the context passed from the caller >> + * @min_order: the minimum order of free lists to check >> + * @report_page_block: the callback function to report free page blocks > page_block has meaning in the core MM which doesn't strictly match its > usage here. Moreover we are reporting pfn ranges rather than struct page > range. So report_pfn_range would suit better. > > [...] >> + for_each_populated_zone(zone) { >> + for (order = MAX_ORDER - 1; order >= min_order; order--) { >> + for (mt = 0; !stop && mt < MIGRATE_TYPES; mt++) { >> + spin_lock_irqsave(&zone->lock, flags); >> + list = &zone->free_area[order].free_list[mt]; >> + list_for_each_entry(page, list, lru) { >> + pfn = page_to_pfn(page); >> + stop = report_page_block(opaque, pfn, >> + 1 << order); >> + if (stop) >> + break; > if (stop) { > spin_unlock_irqrestore(&zone->lock, flags); > return; > } > > would be both easier and less error prone. E.g. You wouldn't pointlessly > iterate over remaining orders just to realize there is nothing to be > done for those... > Yes, that's better, thanks. I will take other suggestions as well. Best, Wei