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Wed, 1 Apr 2020 11:21:37 +0000 (UTC) Received: from [10.36.114.59] (ovpn-114-59.ams2.redhat.com [10.36.114.59]) by smtp.corp.redhat.com (Postfix) with ESMTP id 3BA6E19C6A; Wed, 1 Apr 2020 11:21:29 +0000 (UTC) Subject: Re: [RFC for Linux] virtio_balloon: Add VIRTIO_BALLOON_F_THP_ORDER to handle THP spilt issue To: Nadav Amit References: <20200326031817-mutt-send-email-mst@kernel.org> <20200326054554-mutt-send-email-mst@kernel.org> <20200331091718-mutt-send-email-mst@kernel.org> <02a393ce-c4b4-ede9-7671-76fa4c19097a@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; prefer-encrypt=mutual; keydata= mQINBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABtCREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT6JAlgEEwEIAEICGwMFCQlmAYAGCwkIBwMCBhUI AgkKCwQWAgMBAh4BAheAFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl3pImkCGQEACgkQTd4Q 9wD/g1o+VA//SFvIHUAvul05u6wKv/pIR6aICPdpF9EIgEU448g+7FfDgQwcEny1pbEzAmiw zAXIQ9H0NZh96lcq+yDLtONnXk/bEYWHHUA014A1wqcYNRY8RvY1+eVHb0uu0KYQoXkzvu+s Dncuguk470XPnscL27hs8PgOP6QjG4jt75K2LfZ0eAqTOUCZTJxA8A7E9+XTYuU0hs7QVrWJ jQdFxQbRMrYz7uP8KmTK9/Cnvqehgl4EzyRaZppshruKMeyheBgvgJd5On1wWq4ZUV5PFM4x II3QbD3EJfWbaJMR55jI9dMFa+vK7MFz3rhWOkEx/QR959lfdRSTXdxs8V3zDvChcmRVGN8U Vo93d1YNtWnA9w6oCW1dnDZ4kgQZZSBIjp6iHcA08apzh7DPi08jL7M9UQByeYGr8KuR4i6e RZI6xhlZerUScVzn35ONwOC91VdYiQgjemiVLq1WDDZ3B7DIzUZ4RQTOaIWdtXBWb8zWakt/ ztGhsx0e39Gvt3391O1PgcA7ilhvqrBPemJrlb9xSPPRbaNAW39P8ws/UJnzSJqnHMVxbRZC Am4add/SM+OCP0w3xYss1jy9T+XdZa0lhUvJfLy7tNcjVG/sxkBXOaSC24MFPuwnoC9WvCVQ ZBxouph3kqc4Dt5X1EeXVLeba+466P1fe1rC8MbcwDkoUo65Ag0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAGJAiUEGAECAA8FAlXLn5ECGwwFCQlmAYAACgkQTd4Q 9wD/g1qA6w/+M+ggFv+JdVsz5+ZIc6MSyGUozASX+bmIuPeIecc9UsFRatc91LuJCKMkD9Uv GOcWSeFpLrSGRQ1Z7EMzFVU//qVs6uzhsNk0RYMyS0B6oloW3FpyQ+zOVylFWQCzoyyf227y GW8HnXunJSC+4PtlL2AY4yZjAVAPLK2l6mhgClVXTQ/S7cBoTQKP+jvVJOoYkpnFxWE9pn4t H5QIFk7Ip8TKr5k3fXVWk4lnUi9MTF/5L/mWqdyIO1s7cjharQCstfWCzWrVeVctpVoDfJWp 4LwTuQ5yEM2KcPeElLg5fR7WB2zH97oI6/Ko2DlovmfQqXh9xWozQt0iGy5tWzh6I0JrlcxJ ileZWLccC4XKD1037Hy2FLAjzfoWgwBLA6ULu0exOOdIa58H4PsXtkFPrUF980EEibUp0zFz GotRVekFAceUaRvAj7dh76cToeZkfsjAvBVb4COXuhgX6N4pofgNkW2AtgYu1nUsPAo+NftU CxrhjHtLn4QEBpkbErnXQyMjHpIatlYGutVMS91XTQXYydCh5crMPs7hYVsvnmGHIaB9ZMfB njnuI31KBiLUks+paRkHQlFcgS2N3gkRBzH7xSZ+t7Re3jvXdXEzKBbQ+dC3lpJB0wPnyMcX FOTT3aZT7IgePkt5iC/BKBk3hqKteTnJFeVIT7EC+a6YUFg= Organization: Red Hat GmbH Message-ID: Date: Wed, 1 Apr 2020 13:21:28 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.120 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "pagupta@redhat.com" , "Michael S. Tsirkin" , "jasowang@redhat.com" , "mojha@codeaurora.org" , "qemu-devel@nongnu.org" , LKML , Hui Zhu , Alexander Duyck , Linux Virtualization , "akpm@linux-foundation.org" , Hui Zhu Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 31.03.20 18:27, Nadav Amit wrote: >> On Mar 31, 2020, at 6:32 AM, David Hildenbrand wrot= e: >> >> On 31.03.20 15:24, Michael S. Tsirkin wrote: >>> 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 : >>>>>>> >>>>>>> =EF=BB=BFOn Thu, Mar 12, 2020 at 09:51:25AM +0100, David Hildenbr= and wrote: >>>>>>>>> On 12.03.20 09:47, Michael S. Tsirkin wrote: >>>>>>>>> On Thu, Mar 12, 2020 at 09:37:32AM +0100, David Hildenbrand wro= te: >>>>>>>>>> 2. You are essentially stealing THPs in the guest. So the fast= est >>>>>>>>>> mapping (THP in guest and host) is gone. The guest won't be ab= le 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 prope= r >>>>>>>>>> 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_ord= er, >>>>>>>>> unsigned int max_order, unsigned int *order) >>>>>>>>> >>>>>>>>> the idea would then be to return at a number of pages in the gi= ven >>>>>>>>> range. >>>>>>>>> >>>>>>>>> What do you think? Want to try implementing that? >>>>>>>> >>>>>>>> You can just start with the highest order and decrement the orde= r until >>>>>>>> your allocation succeeds using alloc_pages(), which would be eno= ugh for >>>>>>>> a first version. At least I don't see the immediate need for a n= ew >>>>>>>> kernel API. >>>>>>> >>>>>>> OK I remember now. The problem is with reclaim. Unless reclaim i= s >>>>>>> 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=E2=80=98s a pure optimization IMHO. >>>>>> So I think we should do a trivial implementation first and then se= e what we gain from a new allocator API. Then we might also be able to ju= stify 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,=20 >>>> 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 2= 001 >>>> 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_rep= orting_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 =3D 0; i < VIRTIO_BALLOON_PAGES_PER_PAGE; i++) >>>> + for (i =3D 0; i < VIRTIO_BALLOON_PAGES_PER_PAGE * (1 << order); i+= +) >>>> pfns[i] =3D 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 =3D MAX_ORDER - 1; >>>> unsigned num_pfns; >>>> struct page *page; >>>> LIST_HEAD(pages); >>>> @@ -212,9 +213,20 @@ static unsigned fill_balloon(struct virtio_ball= oon *vb, size_t num) >>>> /* We can only do one array worth at a time. */ >>>> num =3D 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 =3D 0; num_pfns < num; >>>> - num_pfns +=3D VIRTIO_BALLOON_PAGES_PER_PAGE) { >>>> - struct page *page =3D balloon_page_alloc(); >>>> + num_pfns +=3D VIRTIO_BALLOON_PAGES_PER_PAGE * (1 << order)) { >>>> + const unsigned long remaining =3D num - num_pfns; >>>> + >>>> + order =3D MIN(order, >>>> + get_order(remaining << VIRTIO_BALLOON_PFN_SHIFT)); >>>> + if ((1 << order) * VIRTIO_BALLOON_PAGES_PER_PAGE > remaining) >>>> + order--; >>>> + page =3D balloon_pages_alloc(order); >>>> >>>> if (!page) { >>>> dev_info_ratelimited(&vb->vdev->dev, >>>> @@ -225,6 +237,8 @@ static unsigned fill_balloon(struct virtio_ballo= on *vb, size_t num) >>>> break; >>>> } >>>> >>>> + /* Continue with the actual order that succeeded. */ >>>> + order =3D page_private(page); >>>> balloon_page_push(&pages, page); >>>> } >>>> >>>> @@ -233,14 +247,16 @@ static unsigned fill_balloon(struct virtio_bal= loon *vb, size_t num) >>>> vb->num_pfns =3D 0; >>>> >>>> while ((page =3D balloon_page_pop(&pages))) { >>>> + order =3D 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 +=3D VIRTIO_BALLOON_PAGES_PER_PAGE; >>>> + set_page_pfns(vb, vb->pfns + vb->num_pfns, page, order); >>>> + vb->num_pages +=3D 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 +=3D VIRTIO_BALLOON_PAGES_PER_PAGE; >>>> + adjust_managed_page_count(page, -1 * (1 << order)); >>>> + vb->num_pfns +=3D VIRTIO_BALLOON_PAGES_PER_PAGE * (1 << order); >>>> } >>>> >>>> num_allocated_pages =3D vb->num_pfns; >>>> @@ -284,7 +300,7 @@ static unsigned leak_balloon(struct virtio_ballo= on *vb, size_t num) >>>> page =3D 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 -=3D VIRTIO_BALLOON_PAGES_PER_PAGE; >>>> } >>>> @@ -786,7 +802,7 @@ static int virtballoon_migratepage(struct balloo= n_dev_info *vb_dev_info, >>>> __count_vm_event(BALLOON_MIGRATE); >>>> spin_unlock_irqrestore(&vb_dev_info->pages_lock, flags); >>>> vb->num_pfns =3D 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 balloo= n_dev_info *vb_dev_info, >>>> balloon_page_delete(page); >>>> spin_unlock_irqrestore(&vb_dev_info->pages_lock, flags); >>>> vb->num_pfns =3D 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/ball= oon_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 ba= lloon_dev_info *balloon) >>>> balloon->inode =3D 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 balloo= n_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 removin= g 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 =3D alloc_page(balloon_mapping_gfp_mask() | >>>> - __GFP_NOMEMALLOC | __GFP_NORETRY | >>>> - __GFP_NOWARN); >>>> - return page; >>>> + struct page *page; >>>> + >>>> + while (order >=3D 0) { >>>> + page =3D 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 l= ist. >>> >>> >>> I think this will try to invoke direct reclaim from the first iterati= on >>> to free up the max order. >> >> %__GFP_NORETRY: The VM implementation will try only very lightweight >> memory direct reclaim to get some memory under memory pressure (thus i= t >> can sleep). It will avoid disruptive actions like OOM killer. >> >> Certainly good enough for a first version I would say, no? Looking at >> the vmware balloon, they don't even set __GFP_NORETRY. >=20 > Yes, it does seem that we are missing __GFP_NORETRY. I really do not kn= ow > what I was thinking when I did not add it for huge-pages allocation. I = will > send a patch. Thanks for noticing :) >=20 > In regard to your patch, I would be happy to consolidate the allocation > mechanisms, so VMware balloon driver would also use your code. In gener= al > your code looks good, take-away some style issues. Yeah, let's see in which direction we'll be bringing balloon_page_alloc(), I think there are still some questions to be answered (mostly performance implications). Cheers! --=20 Thanks, David / dhildenb