From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754452AbdGNPqg (ORCPT ); Fri, 14 Jul 2017 11:46:36 -0400 Received: from mx1.redhat.com ([209.132.183.28]:53266 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754049AbdGNPqf (ORCPT ); Fri, 14 Jul 2017 11:46:35 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 5971BD43C3 Authentication-Results: ext-mx09.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx09.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=mst@redhat.com DKIM-Filter: OpenDKIM Filter v2.11.0 mx1.redhat.com 5971BD43C3 Date: Fri, 14 Jul 2017 18:46:29 +0300 From: "Michael S. Tsirkin" To: Michal Hocko Cc: Wei Wang , linux-kernel@vger.kernel.org, qemu-devel@nongnu.org, virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, linux-mm@kvack.org, david@redhat.com, cornelia.huck@de.ibm.com, akpm@linux-foundation.org, mgorman@techsingularity.net, aarcange@redhat.com, amit.shah@redhat.com, pbonzini@redhat.com, liliang.opensource@gmail.com, virtio-dev@lists.oasis-open.org, yang.zhang.wz@gmail.com, quan.xu@aliyun.com Subject: Re: [PATCH v12 6/8] mm: support reporting free page blocks Message-ID: <20170714183112-mutt-send-email-mst@kernel.org> References: <1499863221-16206-1-git-send-email-wei.w.wang@intel.com> <1499863221-16206-7-git-send-email-wei.w.wang@intel.com> <20170714123023.GA2624@dhcp22.suse.cz> <20170714125429.GP2618@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170714125429.GP2618@dhcp22.suse.cz> X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Fri, 14 Jul 2017 15:46:34 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 14, 2017 at 02:54:30PM +0200, Michal Hocko wrote: > On Fri 14-07-17 14:30:23, Michal Hocko wrote: > > On Wed 12-07-17 20:40:19, Wei Wang wrote: > > > This patch adds support for reporting blocks of pages on the free list > > > specified by the caller. > > > > > > As pages can leave the free list during this call or immediately > > > afterwards, they are not guaranteed to be free after the function > > > returns. The only guarantee this makes is that the page was on the free > > > list at some point in time after the function has been invoked. > > > > > > Therefore, it is not safe for caller to use any pages on the returned > > > block or to discard data that is put there after the function returns. > > > However, it is safe for caller to discard data that was in one of these > > > pages before the function was invoked. > > > > I do not understand what is the point of such a function and how it is > > used because the patch doesn't give us any user (I haven't checked other > > patches yet). > > > > But just from the semantic point of view this sounds like a horrible > > idea. The only way to get a free block of pages is to call the page > > allocator. I am tempted to give it Nack right on those grounds but I > > would like to hear more about what you actually want to achieve. > > OK, so I gave it another thought and giving a page which is still on the > free list to a random module is just a free ticket to a disaster. > Nacked-by: Michal Hocko I agree it should be EXPORT_SYMBOL_GPL. Too much power to give to non-GPL modules. But pls take a look at the explanation I posted. Any kind of hypervisor hinting will need to do this by definition - best we can do is keep a lock while we do this. > > > > > Signed-off-by: Wei Wang > > > Signed-off-by: Liang Li > > > --- > > > include/linux/mm.h | 5 +++ > > > mm/page_alloc.c | 96 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ > > > 2 files changed, 101 insertions(+) > > > > > > diff --git a/include/linux/mm.h b/include/linux/mm.h > > > index 46b9ac5..76cb433 100644 > > > --- a/include/linux/mm.h > > > +++ b/include/linux/mm.h > > > @@ -1835,6 +1835,11 @@ 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); > > > > > > +#if IS_ENABLED(CONFIG_VIRTIO_BALLOON) > > > +extern int report_unused_page_block(struct zone *zone, unsigned int order, > > > + unsigned int migratetype, > > > + struct page **page); > > > +#endif > > > /* > > > * 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 64b7d82..8b3c9dd 100644 > > > --- a/mm/page_alloc.c > > > +++ b/mm/page_alloc.c > > > @@ -4753,6 +4753,102 @@ void show_free_areas(unsigned int filter, nodemask_t *nodemask) > > > show_swap_cache_info(); > > > } > > > > > > +#if IS_ENABLED(CONFIG_VIRTIO_BALLOON) > > > + > > > +/* > > > + * Heuristically get a page block in the system that is unused. > > > + * It is possible that pages from the page block are used immediately after > > > + * report_unused_page_block() returns. It is the caller's responsibility > > > + * to either detect or prevent the use of such pages. > > > + * > > > + * The free list to check: zone->free_area[order].free_list[migratetype]. > > > + * > > > + * If the caller supplied page block (i.e. **page) is on the free list, offer > > > + * the next page block on the list to the caller. Otherwise, offer the first > > > + * page block on the list. > > > + * > > > + * Note: it is not safe for caller to use any pages on the returned > > > + * block or to discard data that is put there after the function returns. > > > + * However, it is safe for caller to discard data that was in one of these > > > + * pages before the function was invoked. > > > + * > > > + * Return 0 when a page block is found on the caller specified free list. > > > + */ > > > +int report_unused_page_block(struct zone *zone, unsigned int order, > > > + unsigned int migratetype, struct page **page) > > > +{ > > > + struct zone *this_zone; > > > + struct list_head *this_list; > > > + int ret = 0; > > > + unsigned long flags; > > > + > > > + /* Sanity check */ > > > + if (zone == NULL || page == NULL || order >= MAX_ORDER || > > > + migratetype >= MIGRATE_TYPES) > > > + return -EINVAL; > > > + > > > + /* Zone validity check */ > > > + for_each_populated_zone(this_zone) { > > > + if (zone == this_zone) > > > + break; > > > + } > > > + > > > + /* Got a non-existent zone from the caller? */ > > > + if (zone != this_zone) > > > + return -EINVAL; > > > > Huh, what do you check for here? Why don't you simply > > populated_zone(zone)? > > > > > + > > > + spin_lock_irqsave(&this_zone->lock, flags); > > > + > > > + this_list = &zone->free_area[order].free_list[migratetype]; > > > + if (list_empty(this_list)) { > > > + *page = NULL; > > > + ret = 1; > > > + goto out; > > > + } > > > + > > > + /* The caller is asking for the first free page block on the list */ > > > + if ((*page) == NULL) { > > > + *page = list_first_entry(this_list, struct page, lru); > > > + ret = 0; > > > + goto out; > > > + } > > > + > > > + /* > > > + * The page block passed from the caller is not on this free list > > > + * anymore (e.g. a 1MB free page block has been split). In this case, > > > + * offer the first page block on the free list that the caller is > > > + * asking for. > > > + */ > > > + if (PageBuddy(*page) && order != page_order(*page)) { > > > + *page = list_first_entry(this_list, struct page, lru); > > > + ret = 0; > > > + goto out; > > > + } > > > + > > > + /* > > > + * The page block passed from the caller has been the last page block > > > + * on the list. > > > + */ > > > + if ((*page)->lru.next == this_list) { > > > + *page = NULL; > > > + ret = 1; > > > + goto out; > > > + } > > > + > > > + /* > > > + * Finally, fall into the regular case: the page block passed from the > > > + * caller is still on the free list. Offer the next one. > > > + */ > > > + *page = list_next_entry((*page), lru); > > > + ret = 0; > > > +out: > > > + spin_unlock_irqrestore(&this_zone->lock, flags); > > > + return ret; > > > +} > > > +EXPORT_SYMBOL(report_unused_page_block); > > > + > > > +#endif > > > + > > > 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 > > > > -- > > Michal Hocko > > SUSE Labs > > -- > Michal Hocko > SUSE Labs