From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751607AbeAYJdi (ORCPT ); Thu, 25 Jan 2018 04:33:38 -0500 Received: from mga03.intel.com ([134.134.136.65]:57725 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751434AbeAYJdF (ORCPT ); Thu, 25 Jan 2018 04:33:05 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.46,411,1511856000"; d="scan'208";a="12903126" From: Wei Wang To: virtio-dev@lists.oasis-open.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, linux-mm@kvack.org, mst@redhat.com, mhocko@kernel.org, akpm@linux-foundation.org Cc: pbonzini@redhat.com, wei.w.wang@intel.com, liliang.opensource@gmail.com, yang.zhang.wz@gmail.com, quan.xu0@gmail.com, nilal@redhat.com, riel@redhat.com Subject: [PATCH v25 1/2] mm: support reporting free page blocks Date: Thu, 25 Jan 2018 17:14:05 +0800 Message-Id: <1516871646-22741-2-git-send-email-wei.w.wang@intel.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1516871646-22741-1-git-send-email-wei.w.wang@intel.com> References: <1516871646-22741-1-git-send-email-wei.w.wang@intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- 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