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(p200300cbc7398e007a461b8c8b130d3d.dip0.t-ipconnect.de. [2003:cb:c739:8e00:7a46:1b8c:8b13:d3d]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-381ed9ea4f6sm14966580f8f.64.2024.11.12.02.08.44 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 12 Nov 2024 02:08:45 -0800 (PST) Message-ID: <3049bc19-2556-4fbf-9d34-578db523b63b@redhat.com> Date: Tue, 12 Nov 2024 11:08:44 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 2/2] migration: Do not perform RAMBlock dirty sync during the first iteration To: Yong Huang Cc: qemu-devel@nongnu.org, Peter Xu , Fabiano Rosas , Wei Wang , "Michael S . Tsirkin" References: <43700d36-b9f8-42da-ba72-b0ec6580032d@redhat.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz 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+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=david@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.122, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.671, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 11.11.24 12:37, Yong Huang wrote: > > > On Mon, Nov 11, 2024 at 6:42 PM David Hildenbrand > wrote: > > On 11.11.24 11:08, Yong Huang wrote: > > > > > > On Mon, Nov 11, 2024 at 5:27 PM David Hildenbrand > > > >> wrote: > > > >     On 09.11.24 05:59, Hyman Huang wrote: > >      > The first iteration's RAMBlock dirty sync can be omitted > because QEMU > >      > always initializes the RAMBlock's bmap to all 1s by default. > >      > > >      > Signed-off-by: Hyman Huang > >     >> > >      > --- > >      >   migration/cpu-throttle.c |  2 +- > >      >   migration/ram.c          | 11 ++++++++--- > >      >   2 files changed, 9 insertions(+), 4 deletions(-) > >      > > >      > diff --git a/migration/cpu-throttle.c b/migration/cpu- > throttle.c > >      > index 5179019e33..674dc2004e 100644 > >      > --- a/migration/cpu-throttle.c > >      > +++ b/migration/cpu-throttle.c > >      > @@ -141,7 +141,7 @@ void > cpu_throttle_dirty_sync_timer_tick(void > >     *opaque) > >      >        * effect on guest performance, therefore omit it to > avoid > >      >        * paying extra for the sync penalty. > >      >        */ > >      > -    if (sync_cnt <= 1) { > >      > +    if (!sync_cnt) { > >      >           goto end; > >      >       } > >      > > >      > diff --git a/migration/ram.c b/migration/ram.c > >      > index 05ff9eb328..571dba10b7 100644 > >      > --- a/migration/ram.c > >      > +++ b/migration/ram.c > >      > @@ -2718,7 +2718,7 @@ static void ram_list_init_bitmaps(void) > >      >   { > >      >       MigrationState *ms = migrate_get_current(); > >      >       RAMBlock *block; > >      > -    unsigned long pages; > >      > +    unsigned long pages, clear_bmap_pages; > >      >       uint8_t shift; > >      > > >      >       /* Skip setting bitmap if there is no RAM */ > >      > @@ -2736,6 +2736,7 @@ static void ram_list_init_bitmaps(void) > >      > > >      >           RAMBLOCK_FOREACH_NOT_IGNORED(block) { > >      >               pages = block->max_length >> TARGET_PAGE_BITS; > >      > +            clear_bmap_pages = clear_bmap_size(pages, shift); > >      >               /* > >      >                * The initial dirty bitmap for migration > must be > >     set with all > >      >                * ones to make sure we'll migrate every > guest RAM > >     page to > >      > @@ -2751,7 +2752,12 @@ static void ram_list_init_bitmaps(void) > >      >                   block->file_bmap = bitmap_new(pages); > >      >               } > >      >               block->clear_bmap_shift = shift; > >      > -            block->clear_bmap = > >     bitmap_new(clear_bmap_size(pages, shift)); > >      > +            block->clear_bmap = bitmap_new(clear_bmap_pages); > >      > +            /* > >      > +             * Set clear_bmap to 1 unconditionally, as we > always > >     set bmap > >      > +             * to all 1s by default. > >      > +             */ > >      > +            bitmap_set(block->clear_bmap, 0, > clear_bmap_pages); > >      >           } > >      >       } > >      >   } > >      > @@ -2783,7 +2789,6 @@ static bool > ram_init_bitmaps(RAMState *rs, > >     Error **errp) > >      >               if (!ret) { > >      >                   goto out_unlock; > >      >               } > >      > -            migration_bitmap_sync_precopy(false); > >      >           } > >      >       } > >      >   out_unlock: > > > > > >     For virtio-mem, we rely on the > migration_bitmap_clear_discarded_pages() > >     call to clear all bits that correspond to unplugged memory > ranges. > > > > > >     If we ommit the sync, we can likely have bits of unplugged > ranges still > >     set to "1", meaning we would try migrate them later, although we > >     shouldn't? > > > > > > > > IIUC, migration_bitmap_clear_discarded_pagesis still called at > the end of > > ram_init_bitmaps no matter if we omit the first sync. >  > > PRECOPY_NOTIFY_SETUPnotification is sent out at the end of > > ram_save_setup(ram_list_init_bitmaps),when > > virtio_balloon_free_page_start() is > > called,migration_bitmap_clear_discarded_pages() has already > completed > > and the > > bmap has been correctly cleared. > > > > ram_save_setup > >     -> ram_list_init_bitmaps > >         -> migration_bitmap_clear_discarded_pages > >      -> return precopy_notify(PRECOPY_NOTIFY_SETUP, errp); > > > > You can double check it. > > That's not my concern, let me clarify :) > > > Assume in KVM the bitmap is all 1s ("everything dirty"). > > In current code, we will sync the bitmap once (IIRC, clearing any dirty > bits from KVM). > > > For the old logic, write-protect and clear dirty bits are all done in > the KVM_GET_DIRTY_LOG API, while with > KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 feature enabled, clearing > dirty bits are postponed in the KVM_CLEAR_DIRTY_LOG API, which > is called right before page sending in the migration thread in QEMU. > > > Then we call migration_bitmap_clear_discarded_pages() to clear all > "discarded" pages that we shouldn't touch. > > When we do the next bitmap sync, we will not get a "1" for discarded > ranges, and we will never try migrating discarded ranges. > > > With your patch, we're omitting the first sync. Could we possibly get > discarded ranges reported from KVM as dirty during the "now first" sync > *after* the migration_bitmap_clear_discarded_pages() call, and try > migrating discarded ranges? > > I did not dive deep into the code, maybe > migration_bitmap_clear_discarded_pages() ends up clearing the bits in > > > Yes, the migration_bitmap_clear_discarded_pages clear the bits in > KVM in: > ramblock_dirty_bitmap_clear_discarded_pages >     -> dirty_bitmap_clear_section >         -> migration_clear_memory_region_dirty_bitmap_range >             -> migration_clear_memory_region_dirty_bitmap >                 -> memory_region_clear_dirty_bitmap >                     -> KVM_CLEAR_DIRTY_LOG ioctl > I just tried, and your patch breaks virtio-mem migration as I suspected. sudo build/qemu-system-x86_64 \ --enable-kvm \ -m 16G,maxmem=24G \ -object memory-backend-ram,id=mem1,size=16G \ -machine q35,memory-backend=mem1 \ -cpu max \ -smp 16 \ -nographic \ -nodefaults \ -net nic -net user \ -chardev stdio,nosignal,id=serial \ -hda Fedora-Server-KVM-40-1.14.x86_64.qcow2 \ -cdrom /home/dhildenb/git/cloud-init/cloud-init.iso \ -device isa-serial,chardev=serial \ -chardev socket,id=monitor,path=/var/tmp/mon_src,server,nowait \ -mon chardev=monitor,mode=readline \ -device pcie-root-port,id=root,slot=0 \ -object memory-backend-file,share=on,mem-path=/dev/shm/vm,id=mem2,size=8G \ -device virtio-mem-pci,id=vmem0,memdev=mem2,requested-size=16M,bus=root,dynamic-memslots=on,prealloc=on \ Once the VM booted up, as expected we're consuming 16M $ stat /dev/shm/vm Datei: /dev/shm/vm Größe: 8589934592 Blöcke: 32768 EA Block: 4096 reguläre Datei Gerät: 0/25 Inode: 2087 Verknüpfungen: 1 tmpfs tmpfs 16G 16M 16G 1% /dev/shm Let's start a migration: $ echo "migrate exec:cat>state" | sudo nc -U /var/tmp/mon_src ... and we end up reading discarded memory: $ LANG=C df -ahT | grep /dev/shm tmpfs tmpfs 16G 8.0G 7.6G 52% /dev/shm Running with TCG only also doesn't work. So somewhere, we have a bitmap filled with all 1s that is not cleared if we drop the first sync. -- Cheers, David / dhildenb