From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751411AbdH1Ndb (ORCPT ); Mon, 28 Aug 2017 09:33:31 -0400 Received: from mx2.suse.de ([195.135.220.15]:56965 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751171AbdH1Nda (ORCPT ); Mon, 28 Aug 2017 09:33:30 -0400 Date: Mon, 28 Aug 2017 15:33:26 +0200 From: Michal Hocko To: Wei Wang 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 Subject: Re: [PATCH v15 4/5] mm: support reporting free page blocks Message-ID: <20170828133326.GN17097@dhcp22.suse.cz> References: <1503914913-28893-1-git-send-email-wei.w.wang@intel.com> <1503914913-28893-5-git-send-email-wei.w.wang@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1503914913-28893-5-git-send-email-wei.w.wang@intel.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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... > + } > + spin_unlock_irqrestore(&zone->lock, flags); > + } > + } > + } > +} > +EXPORT_SYMBOL_GPL(walk_free_mem_block); -- Michal Hocko SUSE Labs