From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f72.google.com (mail-oi0-f72.google.com [209.85.218.72]) by kanga.kvack.org (Postfix) with ESMTP id 00EEE800DD for ; Thu, 25 Jan 2018 08:47:05 -0500 (EST) Received: by mail-oi0-f72.google.com with SMTP id b193so4044106oii.12 for ; Thu, 25 Jan 2018 05:47:04 -0800 (PST) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id d9si2292470oia.322.2018.01.25.05.47.03 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 25 Jan 2018 05:47:03 -0800 (PST) Date: Thu, 25 Jan 2018 15:46:56 +0200 From: "Michael S. Tsirkin" Subject: Re: [PATCH v25 1/2] mm: support reporting free page blocks Message-ID: <20180125154623-mutt-send-email-mst@kernel.org> References: <1516871646-22741-1-git-send-email-wei.w.wang@intel.com> <1516871646-22741-2-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: <1516871646-22741-2-git-send-email-wei.w.wang@intel.com> Sender: owner-linux-mm@kvack.org List-ID: To: Wei Wang Cc: virtio-dev@lists.oasis-open.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, linux-mm@kvack.org, mhocko@kernel.org, akpm@linux-foundation.org, pbonzini@redhat.com, liliang.opensource@gmail.com, yang.zhang.wz@gmail.com, quan.xu0@gmail.com, nilal@redhat.com, riel@redhat.com On Thu, Jan 25, 2018 at 05:14:05PM +0800, 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. > > Signed-off-by: Wei Wang > Signed-off-by: Liang Li > Cc: Michal Hocko > Cc: Michael S. Tsirkin > Acked-by: Michal Hocko Commented on v24 that this should be restartable. That comment still applies. > --- > include/linux/mm.h | 6 ++++ > mm/page_alloc.c | 96 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 102 insertions(+) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index ea818ff..e65ae2e 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1938,6 +1938,12 @@ extern void free_area_init_node(int nid, unsigned long * zones_size, > unsigned long zone_start_pfn, unsigned long *zholes_size); > extern void free_initmem(void); > > +extern int walk_free_mem_block(void *opaque, > + int min_order, > + int (*report_pfn_range)(void *opaque, > + unsigned long pfn, > + unsigned long num)); > + > /* > * 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 76c9688..0f08039 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -4899,6 +4899,102 @@ void show_free_areas(unsigned int filter, nodemask_t *nodemask) > show_swap_cache_info(); > } > > +/* > + * Walk through a free page list and report the found pfn range via the > + * callback. > + * > + * Return 0 if it completes the reporting. Otherwise, return the Non-zero > + * value returned from the callback. > + */ > +static int walk_free_page_list(void *opaque, > + struct zone *zone, > + int order, > + enum migratetype mt, > + int (*report_pfn_range)(void *, > + unsigned long, > + unsigned long)) > +{ > + struct page *page; > + struct list_head *list; > + unsigned long pfn, flags; > + bool ret = 0; > + > + 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); > + ret = report_pfn_range(opaque, pfn, 1 << order); > + if (ret) > + break; > + } > + spin_unlock_irqrestore(&zone->lock, flags); > + > + return ret; > +} > + > +/** > + * 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_pfn_range: the callback to report the pfn range of the free pages > + * > + * If the callback returns a non-zero value, stop iterating the list of free > + * page blocks. Otherwise, continue to report. > + * > + * Please note that there are no locking guarantees for the callback and > + * that the reported pfn range might be freed or disappear after the > + * callback returns so the caller has to be very careful how it is used. > + * > + * The callback itself must not sleep or perform any operations which would > + * require any memory allocations directly (not even GFP_NOWAIT/GFP_ATOMIC) > + * or via any lock dependency. It is generally advisable to implement > + * the callback as simple as possible and defer any heavy lifting to a > + * different context. > + * > + * There is no guarantee that each free range will be reported only once > + * during one walk_free_mem_block invocation. > + * > + * pfn_to_page on the given range is strongly discouraged and if there is > + * an absolute need for that make sure to contact MM people to discuss > + * potential problems. > + * > + * The function itself might sleep so it cannot be called from atomic > + * contexts. > + * > + * In general low orders tend to be very volatile and so it makes more > + * sense to query larger ones first for various optimizations which like > + * ballooning etc... This will reduce the overhead as well. > + * > + * Return 0 if it completes the reporting. Otherwise, return the non-zero > + * value returned from the callback. > + */ > +int walk_free_mem_block(void *opaque, > + int min_order, > + int (*report_pfn_range)(void *opaque, > + unsigned long pfn, > + unsigned long num)) > +{ > + struct zone *zone; > + int order; > + enum migratetype mt; > + bool ret; > + > + for_each_populated_zone(zone) { > + for (order = MAX_ORDER - 1; order >= min_order; order--) { > + for (mt = 0; mt < MIGRATE_TYPES; mt++) { > + ret = walk_free_page_list(opaque, zone, > + order, mt, > + report_pfn_range); > + if (ret) > + return ret; > + } > + } > + } > + > + return 0; > +} > +EXPORT_SYMBOL_GPL(walk_free_mem_block); > + > static void zoneref_set_zone(struct zone *zone, struct zoneref *zoneref) > { > zoneref->zone = zone; > -- > 2.7.4 -- 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