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Mon, 31 Mar 2025 15:19:00 +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 TAyqHWSy6mdtSAAAD6G6ig (envelope-from ); Mon, 31 Mar 2025 15:19:00 +0000 From: Fabiano Rosas To: Prasad Pandit , qemu-devel@nongnu.org Cc: peterx@redhat.com, berrange@redhat.com Subject: Re: [PATCH v8 7/7] migration/ram: Implement save_postcopy_prepare() In-Reply-To: <20250318123846.1370312-8-ppandit@redhat.com> References: <20250318123846.1370312-1-ppandit@redhat.com> <20250318123846.1370312-8-ppandit@redhat.com> Date: Mon, 31 Mar 2025 12:18:57 -0300 Message-ID: <87semtkz32.fsf@suse.de> MIME-Version: 1.0 Content-Type: text/plain X-Spamd-Result: default: False [-4.30 / 50.00]; BAYES_HAM(-3.00)[99.99%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; MISSING_XM_UA(0.00)[]; TO_DN_SOME(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_TLS_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; RCPT_COUNT_THREE(0.00)[4]; RCVD_COUNT_TWO(0.00)[2]; FUZZY_BLOCKED(0.00)[rspamd.com]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo,suse.de:mid] Received-SPF: pass client-ip=195.135.223.131; envelope-from=farosas@suse.de; helo=smtp-out2.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, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_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 Prasad Pandit writes: > From: Peter Xu > > Implement save_postcopy_prepare(), preparing for the enablement of both > multifd and postcopy. > > Please see the rich comment for the rationals. > > Signed-off-by: Peter Xu > Signed-off-by: Prasad Pandit > --- > migration/ram.c | 37 +++++++++++++++++++++++++++++++++++++ > 1 file changed, 37 insertions(+) > > v8: > - New patch > > v7: > - https://lore.kernel.org/qemu-devel/20250228121749.553184-1-ppandit@redhat.com/T/#t > > diff --git a/migration/ram.c b/migration/ram.c > index 6fd88cbf2a..04fde7ba6b 100644 > --- a/migration/ram.c > +++ b/migration/ram.c > @@ -4419,6 +4419,42 @@ static int ram_resume_prepare(MigrationState *s, void *opaque) > return 0; > } > > +static bool ram_save_postcopy_prepare(QEMUFile *f, void *opaque, Error **errp) > +{ > + int ret; > + > + if (migrate_multifd()) { > + /* > + * When multifd is enabled, source QEMU needs to make sure all the > + * pages queued before postcopy starts to be flushed. s/to be/have been/ > + * > + * Meanwhile, the load of these pages must happen before switching s/Meanwhile,// > + * to postcopy. It's because loading of guest pages (so far) in > + * multifd recv threads is still non-atomic, so the load cannot > + * happen with vCPUs running on destination side. > + * > + * This flush and sync will guarantee those pages loaded _before_ s/loaded/are loaded/ > + * postcopy starts on destination. The rational is, this happens s/rational/rationale/ > + * before VM stops (and before source QEMU sends all the rest of > + * the postcopy messages). So when the destination QEMU received > + * the postcopy messages, it must have received the sync message on > + * the main channel (either RAM_SAVE_FLAG_MULTIFD_FLUSH, or > + * RAM_SAVE_FLAG_EOS), and such message should have guaranteed all > + * previous guest pages queued in the multifd channels to be > + * completely loaded. > + */ > + ret = multifd_ram_flush_and_sync(f); > + if (ret < 0) { > + error_setg(errp, "%s: multifd flush and sync failed", __func__); > + return false; > + } > + } > + > + qemu_put_be64(f, RAM_SAVE_FLAG_EOS); > + > + return true; > +} > + > void postcopy_preempt_shutdown_file(MigrationState *s) > { > qemu_put_be64(s->postcopy_qemufile_src, RAM_SAVE_FLAG_EOS); > @@ -4438,6 +4474,7 @@ static SaveVMHandlers savevm_ram_handlers = { > .load_setup = ram_load_setup, > .load_cleanup = ram_load_cleanup, > .resume_prepare = ram_resume_prepare, > + .save_postcopy_prepare = ram_save_postcopy_prepare, > }; > > static void ram_mig_ram_block_resized(RAMBlockNotifier *n, void *host,