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Tsirkin" 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 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> <20200331093300-mutt-send-email-mst@kernel.org> <20200331100359-mutt-send-email-mst@kernel.org> 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: <85f699d4-459a-a319-0a8f-96c87d345c49@redhat.com> Date: Tue, 31 Mar 2020 16:09:59 +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: <20200331100359-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Content-Transfer-Encoding: quoted-printable Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 31.03.20 16:07, Michael S. Tsirkin wrote: > On Tue, Mar 31, 2020 at 04:03:18PM +0200, David Hildenbrand wrote: >> On 31.03.20 15:37, Michael S. Tsirkin wrote: >>> On Tue, Mar 31, 2020 at 03:32:05PM +0200, David Hildenbrand wrote: >>>> 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 Hilden= brand wrote: >>>>>>>>>>> On 12.03.20 09:47, Michael S. Tsirkin wrote: >>>>>>>>>>> On Thu, Mar 12, 2020 at 09:37:32AM +0100, David Hildenbrand w= rote: >>>>>>>>>>>> 2. You are essentially stealing THPs in the guest. So the fa= stest >>>>>>>>>>>> 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 th= is implies a >>>>>>>>>>>> performance degradation for some workloads. This needs a pro= per >>>>>>>>>>>> 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 *orde= r) >>>>>>>>>>> >>>>>>>>>>> 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 or= der until >>>>>>>>>> your allocation succeeds using alloc_pages(), which would be e= nough 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 wak= es 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 = 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? >>>>>> diff --git a/include/linux/balloon_compaction.h b/include/linux/ba= lloon_compaction.h >>> >>> ..... >>> >>> >>>>>> 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 ball= oon_dev_info *b_dev_info, >>>>>> EXPORT_SYMBOL_GPL(balloon_page_list_dequeue); >>>>>> =20 >>>>>> /* >>>>>> - * balloon_page_alloc - allocates a new page for insertion into t= he balloon >>>>>> - * page list. >>>>>> + * balloon_pages_alloc - allocates a new page (of at most the giv= en order) >>>>>> + * for insertion into the balloon page list. >>>>>> * >>>>>> * Driver must call this function to properly allocate a new ball= oon page. >>>>>> * Driver must call balloon_page_enqueue before definitively remo= ving the page >>>>>> * from the guest system. >>>>>> * >>>>>> + * Will fall back to smaller orders if allocation fails. The orde= r of the >>>>>> + * allocated page is stored in page->private. >>>>>> + * >>>>>> * Return: struct page for the allocated page or NULL on allocati= on 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); >>>>>> =20 >>>>>> /* >>>>>> * balloon_page_enqueue - inserts a new page into the balloon pag= e list. >>>>> >>>>> >>>>> I think this will try to invoke direct reclaim from the first itera= tion >>>>> 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= it >>>> can sleep). It will avoid disruptive actions like OOM killer. >>>> >>>> Certainly good enough for a first version I would say, no? >>> >>> Frankly how well that behaves would depend a lot on the workload. >>> Can regress just as well. >>> >>> For the 1st version I'd prefer something that is the least disruptive= , >>> and that IMHO means we only trigger reclaim at all in the same config= uration >>> as now - when we can't satisfy the lowest order allocation. >> >> Agreed. >> >>> >>> Anything else would be a huge amount of testing with all kind of >>> workloads. >>> >> >> So doing a "& ~__GFP_RECLAIM" in case order > 0? (as done in >> GFP_TRANSHUGE_LIGHT) >=20 > That will improve the situation when reclaim is not needed, but leave > the problem in place for when it's needed: if reclaim does trigger, we > can get a huge free page and immediately break it up. >=20 > So it's ok as a first step but it will make the second step harder as > we'll need to test with reclaim :). I expect the whole "steal huge pages from your guest" to be problematic, as I already mentioned to Alex. This needs a performance evaluation. This all smells like a lot of workload dependent fine-tuning. :) --=20 Thanks, David / dhildenb