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Wed, 21 Feb 2024 13:24:08 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id AzYWGXj51WWrcgAAD6G6ig (envelope-from ); Wed, 21 Feb 2024 13:24:08 +0000 From: Fabiano Rosas To: Markus Armbruster Cc: qemu-devel@nongnu.org, berrange@redhat.com, Peter Xu , Claudio Fontana , Eric Blake Subject: Re: [PATCH v4 11/34] migration/ram: Introduce 'fixed-ram' migration capability In-Reply-To: <87o7caxl97.fsf@pond.sub.org> References: <20240220224138.24759-1-farosas@suse.de> <20240220224138.24759-12-farosas@suse.de> <87o7caxl97.fsf@pond.sub.org> Date: Wed, 21 Feb 2024 10:24:05 -0300 Message-ID: <87sf1mar2i.fsf@suse.de> MIME-Version: 1.0 Content-Type: text/plain Authentication-Results: smtp-out1.suse.de; dkim=pass header.d=suse.de header.s=susede2_rsa header.b=DTQn1wBW; dkim=pass header.d=suse.de header.s=susede2_ed25519 header.b=d+4nAevd X-Spamd-Result: default: False [-3.31 / 50.00]; ARC_NA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; SPAMHAUS_XBL(0.00)[2a07:de40:b281:104:10:150:64:97:from]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; BAYES_HAM(-3.00)[100.00%]; MIME_GOOD(-0.10)[text/plain]; RCPT_COUNT_FIVE(0.00)[6]; RCVD_COUNT_THREE(0.00)[3]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; DKIM_TRACE(0.00)[suse.de:+]; MX_GOOD(-0.01)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:dkim,suse.de:email]; FUZZY_BLOCKED(0.00)[rspamd.com]; FROM_EQ_ENVFROM(0.00)[]; MIME_TRACE(0.00)[0:+]; RCVD_TLS_ALL(0.00)[]; MID_RHS_MATCH_FROM(0.00)[] X-Rspamd-Server: rspamd1.dmz-prg2.suse.org X-Rspamd-Queue-Id: 2AB4221EF9 Received-SPF: pass client-ip=195.135.223.130; envelope-from=farosas@suse.de; helo=smtp-out1.suse.de X-Spam_score_int: -43 X-Spam_score: -4.4 X-Spam_bar: ---- X-Spam_report: (-4.4 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_MED=-2.3, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 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 Markus Armbruster writes: > Fabiano Rosas writes: > >> Add a new migration capability 'fixed-ram'. >> >> The core of the feature is to ensure that each RAM page has a specific >> offset in the resulting migration stream. The reasons why we'd want >> such behavior are: >> >> - The resulting file will have a bounded size, since pages which are >> dirtied multiple times will always go to a fixed location in the >> file, rather than constantly being added to a sequential >> stream. This eliminates cases where a VM with, say, 1G of RAM can >> result in a migration file that's 10s of GBs, provided that the >> workload constantly redirties memory. >> >> - It paves the way to implement O_DIRECT-enabled save/restore of the >> migration stream as the pages are ensured to be written at aligned >> offsets. >> >> - It allows the usage of multifd so we can write RAM pages to the >> migration file in parallel. >> >> For now, enabling the capability has no effect. The next couple of >> patches implement the core functionality. >> >> Signed-off-by: Fabiano Rosas > > [...] > >> diff --git a/qapi/migration.json b/qapi/migration.json >> index 5a565d9b8d..3fce5fe53e 100644 >> --- a/qapi/migration.json >> +++ b/qapi/migration.json >> @@ -531,6 +531,10 @@ >> # and can result in more stable read performance. Requires KVM >> # with accelerator property "dirty-ring-size" set. (Since 8.1) >> # >> +# @fixed-ram: Migrate using fixed offsets in the migration file for >> +# each RAM page. Requires a migration URI that supports seeking, >> +# such as a file. (since 9.0) >> +# >> # Features: >> # >> # @deprecated: Member @block is deprecated. Use blockdev-mirror with >> @@ -555,7 +559,7 @@ >> { 'name': 'x-ignore-shared', 'features': [ 'unstable' ] }, >> 'validate-uuid', 'background-snapshot', >> 'zero-copy-send', 'postcopy-preempt', 'switchover-ack', >> - 'dirty-limit'] } >> + 'dirty-limit', 'fixed-ram'] } >> >> ## >> # @MigrationCapabilityStatus: > > Can we find a better name than @fixed-ram? @fixed-ram-offsets? > @use-seek? I have no idea how we came to fixed-ram. The archives don't provide any clarification. I find it confusing at first glance as well. A little brainstorming on how fixed-ram is different from exiting migration: Fixed-ram: uses a file, like the 'file:' migration; needs a seeking medium, such as a file; migrates ram by placing a page always in the same offset in the file, contrary to normal migration which streams the page changes continuously; ensures a migration file of size bounded to VM RAM size, contrary to normal 'file:' migration which creates a file with unbounded size; enables multi-threaded RAM migration, even though we only use it when multifd is enabled; uses scatter-gatter APIs (pwritev, preadv); So a few options: (disconsidering use-seek, it might be even more generic/vague) - fixed-ram-offsets - non-streaming (or streaming: false) - ram-scatter-gather (ram-sg) - parallel-ram (even with the slight inaccuracy that we sometimes do it single-threaded) Remember we also use this name internally, so I think a broader "feature" name is better that a super specific one. Does anyone have a strong preference? Other suggestions? > Apart from that, QAPI schema > Acked-by: Markus Armbruster Thanks!