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[79.176.51.222]) by smtp.gmail.com with ESMTPSA id b199sm4202969wme.23.2020.03.31.06.24.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 31 Mar 2020 06:24:40 -0700 (PDT) Date: Tue, 31 Mar 2020 09:24:37 -0400 From: "Michael S. Tsirkin" To: David Hildenbrand Cc: Hui Zhu , jasowang@redhat.com, akpm@linux-foundation.org, pagupta@redhat.com, mojha@codeaurora.org, namit@vmware.com, virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, qemu-devel@nongnu.org, Hui Zhu , Alexander Duyck Subject: Re: [RFC for Linux] virtio_balloon: Add VIRTIO_BALLOON_F_THP_ORDER to handle THP spilt issue Message-ID: <20200331091718-mutt-send-email-mst@kernel.org> References: <20200326031817-mutt-send-email-mst@kernel.org> <20200326054554-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Mar 31, 2020 at 12:35:24PM +0200, David Hildenbrand wrote: > On 26.03.20 10:49, Michael S. Tsirkin wrote: > > On Thu, Mar 26, 2020 at 08:54:04AM +0100, David Hildenbrand wrote: > >> > >> > >>> Am 26.03.2020 um 08:21 schrieb Michael S. Tsirkin : > >>> > >>> On Thu, Mar 12, 2020 at 09:51:25AM +0100, David Hildenbrand wrote: > >>>>> On 12.03.20 09:47, Michael S. Tsirkin wrote: > >>>>> On Thu, Mar 12, 2020 at 09:37:32AM +0100, David Hildenbrand wrote: > >>>>>> 2. You are essentially stealing THPs in the guest. So the fastest > >>>>>> mapping (THP in guest and host) is gone. The guest won't be able to make > >>>>>> use of THP where it previously was able to. I can imagine this implies a > >>>>>> performance degradation for some workloads. This needs a proper > >>>>>> performance evaluation. > >>>>> > >>>>> I think the problem is more with the alloc_pages API. > >>>>> That gives you exactly the given order, and if there's > >>>>> a larger chunk available, it will split it up. > >>>>> > >>>>> But for balloon - I suspect lots of other users, > >>>>> we do not want to stress the system but if a large > >>>>> chunk is available anyway, then we could handle > >>>>> that more optimally by getting it all in one go. > >>>>> > >>>>> > >>>>> So if we want to address this, IMHO this calls for a new API. > >>>>> Along the lines of > >>>>> > >>>>> struct page *alloc_page_range(gfp_t gfp, unsigned int min_order, > >>>>> unsigned int max_order, unsigned int *order) > >>>>> > >>>>> the idea would then be to return at a number of pages in the given > >>>>> range. > >>>>> > >>>>> What do you think? Want to try implementing that? > >>>> > >>>> You can just start with the highest order and decrement the order until > >>>> your allocation succeeds using alloc_pages(), which would be enough for > >>>> a first version. At least I don't see the immediate need for a new > >>>> kernel API. > >>> > >>> OK I remember now. The problem is with reclaim. Unless reclaim is > >>> completely disabled, any of these calls can sleep. After it wakes up, > >>> we would like to get the larger order that has become available > >>> meanwhile. > >>> > >> > >> Yes, but that‘s a pure optimization IMHO. > >> So I think we should do a trivial implementation first and then see what we gain from a new allocator API. Then we might also be able to justify it using real numbers. > >> > > > > Well how do you propose implement the necessary semantics? > > I think we are both agreed that alloc_page_range is more or > > less what's necessary anyway - so how would you approximate it > > on top of existing APIs? > > Looking at drivers/misc/vmw_balloon.c:vmballoon_inflate(), it first > tries to allocate huge pages using > > alloc_pages(__GFP_HIGHMEM|__GFP_NOWARN| __GFP_NOMEMALLOC, > VMW_BALLOON_2M_ORDER) > > And then falls back to 4k allocations (balloon_page_alloc()) in case > allocation fails. > > I'm roughly thinking of something like the following, but with an > optimized reporting interface/bigger pfn array so we can report > > 1MB at a time. Also, it might make sense to remember the order that > succeeded across some fill_balloon() calls. > > Don't even expect it to compile ... > > > > >From 4305f989672ccca4be9293e6d4167e929f3e299b Mon Sep 17 00:00:00 2001 > From: David Hildenbrand > Date: Tue, 31 Mar 2020 12:28:07 +0200 > Subject: [PATCH RFC] tmp > > Signed-off-by: David Hildenbrand > --- > drivers/virtio/virtio_balloon.c | 38 ++++++++++++++++++-------- > include/linux/balloon_compaction.h | 7 ++++- > mm/balloon_compaction.c | 43 +++++++++++++++++++++++------- > 3 files changed, 67 insertions(+), 21 deletions(-) > > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c > index 8511d258dbb4..0660b1b988f0 100644 > --- a/drivers/virtio/virtio_balloon.c > +++ b/drivers/virtio/virtio_balloon.c > @@ -187,7 +187,7 @@ int virtballoon_free_page_report(struct page_reporting_dev_info *pr_dev_info, > } > > static void set_page_pfns(struct virtio_balloon *vb, > - __virtio32 pfns[], struct page *page) > + __virtio32 pfns[], struct page *page, int order) > { > unsigned int i; > > @@ -197,7 +197,7 @@ static void set_page_pfns(struct virtio_balloon *vb, > * Set balloon pfns pointing at this page. > * Note that the first pfn points at start of the page. > */ > - for (i = 0; i < VIRTIO_BALLOON_PAGES_PER_PAGE; i++) > + for (i = 0; i < VIRTIO_BALLOON_PAGES_PER_PAGE * (1 << order); i++) > pfns[i] = cpu_to_virtio32(vb->vdev, > page_to_balloon_pfn(page) + i); > } > @@ -205,6 +205,7 @@ static void set_page_pfns(struct virtio_balloon *vb, > static unsigned fill_balloon(struct virtio_balloon *vb, size_t num) > { > unsigned num_allocated_pages; > + int order = MAX_ORDER - 1; > unsigned num_pfns; > struct page *page; > LIST_HEAD(pages); > @@ -212,9 +213,20 @@ static unsigned fill_balloon(struct virtio_balloon *vb, size_t num) > /* We can only do one array worth at a time. */ > num = min(num, ARRAY_SIZE(vb->pfns)); > > + /* > + * Note: we will currently never allocate more than 1MB due to the > + * pfn array size, so we will not allocate MAX_ORDER - 1 ... > + */ > + > for (num_pfns = 0; num_pfns < num; > - num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) { > - struct page *page = balloon_page_alloc(); > + num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE * (1 << order)) { > + const unsigned long remaining = num - num_pfns; > + > + order = MIN(order, > + get_order(remaining << VIRTIO_BALLOON_PFN_SHIFT)); > + if ((1 << order) * VIRTIO_BALLOON_PAGES_PER_PAGE > remaining) > + order--; > + page = balloon_pages_alloc(order); > > if (!page) { > dev_info_ratelimited(&vb->vdev->dev, > @@ -225,6 +237,8 @@ static unsigned fill_balloon(struct virtio_balloon *vb, size_t num) > break; > } > > + /* Continue with the actual order that succeeded. */ > + order = page_private(page); > balloon_page_push(&pages, page); > } > > @@ -233,14 +247,16 @@ static unsigned fill_balloon(struct virtio_balloon *vb, size_t num) > vb->num_pfns = 0; > > while ((page = balloon_page_pop(&pages))) { > + order = page_order(page); > + /* enqueuing will split the page and clear the order */ > balloon_page_enqueue(&vb->vb_dev_info, page); > > - set_page_pfns(vb, vb->pfns + vb->num_pfns, page); > - vb->num_pages += VIRTIO_BALLOON_PAGES_PER_PAGE; > + set_page_pfns(vb, vb->pfns + vb->num_pfns, page, order); > + vb->num_pages += VIRTIO_BALLOON_PAGES_PER_PAGE * (1 << order); > if (!virtio_has_feature(vb->vdev, > VIRTIO_BALLOON_F_DEFLATE_ON_OOM)) > - adjust_managed_page_count(page, -1); > - vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE; > + adjust_managed_page_count(page, -1 * (1 << order)); > + vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE * (1 << order); > } > > num_allocated_pages = vb->num_pfns; > @@ -284,7 +300,7 @@ static unsigned leak_balloon(struct virtio_balloon *vb, size_t num) > page = balloon_page_dequeue(vb_dev_info); > if (!page) > break; > - set_page_pfns(vb, vb->pfns + vb->num_pfns, page); > + set_page_pfns(vb, vb->pfns + vb->num_pfns, page, 0); > list_add(&page->lru, &pages); > vb->num_pages -= VIRTIO_BALLOON_PAGES_PER_PAGE; > } > @@ -786,7 +802,7 @@ static int virtballoon_migratepage(struct balloon_dev_info *vb_dev_info, > __count_vm_event(BALLOON_MIGRATE); > spin_unlock_irqrestore(&vb_dev_info->pages_lock, flags); > vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE; > - set_page_pfns(vb, vb->pfns, newpage); > + set_page_pfns(vb, vb->pfns, newpage, 0); > tell_host(vb, vb->inflate_vq); > > /* balloon's page migration 2nd step -- deflate "page" */ > @@ -794,7 +810,7 @@ static int virtballoon_migratepage(struct balloon_dev_info *vb_dev_info, > balloon_page_delete(page); > spin_unlock_irqrestore(&vb_dev_info->pages_lock, flags); > vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE; > - set_page_pfns(vb, vb->pfns, page); > + set_page_pfns(vb, vb->pfns, page, 0); > tell_host(vb, vb->deflate_vq); > > mutex_unlock(&vb->balloon_lock); > diff --git a/include/linux/balloon_compaction.h b/include/linux/balloon_compaction.h > index 338aa27e4773..ed93fe5704d1 100644 > --- a/include/linux/balloon_compaction.h > +++ b/include/linux/balloon_compaction.h > @@ -60,7 +60,7 @@ struct balloon_dev_info { > struct inode *inode; > }; > > -extern struct page *balloon_page_alloc(void); > +extern struct page *balloon_pages_alloc(int order); > extern void balloon_page_enqueue(struct balloon_dev_info *b_dev_info, > struct page *page); > extern struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info); > @@ -78,6 +78,11 @@ static inline void balloon_devinfo_init(struct balloon_dev_info *balloon) > balloon->inode = NULL; > } > > +static inline struct page *balloon_page_alloc(void) > +{ > + return balloon_pages_alloc(0); > +} > + > #ifdef CONFIG_BALLOON_COMPACTION > extern const struct address_space_operations balloon_aops; > extern bool balloon_page_isolate(struct page *page, > diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c > index 26de020aae7b..067810b32813 100644 > --- a/mm/balloon_compaction.c > +++ b/mm/balloon_compaction.c > @@ -112,23 +112,35 @@ size_t balloon_page_list_dequeue(struct balloon_dev_info *b_dev_info, > EXPORT_SYMBOL_GPL(balloon_page_list_dequeue); > > /* > - * balloon_page_alloc - allocates a new page for insertion into the balloon > - * page list. > + * balloon_pages_alloc - allocates a new page (of at most the given order) > + * for insertion into the balloon page list. > * > * Driver must call this function to properly allocate a new balloon page. > * Driver must call balloon_page_enqueue before definitively removing the page > * from the guest system. > * > + * Will fall back to smaller orders if allocation fails. The order of the > + * allocated page is stored in page->private. > + * > * Return: struct page for the allocated page or NULL on allocation failure. > */ > -struct page *balloon_page_alloc(void) > +struct page *balloon_pages_alloc(int order) > { > - struct page *page = alloc_page(balloon_mapping_gfp_mask() | > - __GFP_NOMEMALLOC | __GFP_NORETRY | > - __GFP_NOWARN); > - return page; > + struct page *page; > + > + while (order >= 0) { > + page = alloc_pages(balloon_mapping_gfp_mask() | > + __GFP_NOMEMALLOC | __GFP_NORETRY | > + __GFP_NOWARN, order); > + if (page) { > + set_page_private(page, order); > + return page; > + } > + order--; > + } > + return NULL; > } > -EXPORT_SYMBOL_GPL(balloon_page_alloc); > +EXPORT_SYMBOL_GPL(balloon_pages_alloc); > > /* > * balloon_page_enqueue - inserts a new page into the balloon page list. I think this will try to invoke direct reclaim from the first iteration to free up the max order. > @@ -146,10 +158,23 @@ EXPORT_SYMBOL_GPL(balloon_page_alloc); > void balloon_page_enqueue(struct balloon_dev_info *b_dev_info, > struct page *page) > { > + const int order = page_private(page); > unsigned long flags; > + int i; > + > + /* > + * We can only migrate single pages - and even if we could migrate > + * bigger ones, we would want to split them on demand instead of > + * trying to move around big chunks. > + */ > + if (order > 0) > + split_page(page, order); > + set_page_private(page, order); > > spin_lock_irqsave(&b_dev_info->pages_lock, flags); > - balloon_page_enqueue_one(b_dev_info, page); > + for (i = 0; i < (1 << order); i++) > + balloon_page_enqueue_one(b_dev_info, page + i); > + > spin_unlock_irqrestore(&b_dev_info->pages_lock, flags); > } > EXPORT_SYMBOL_GPL(balloon_page_enqueue); > -- > 2.25.1 > > -- > Thanks, > > David / dhildenb