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bh=LBhs9K7cDJCD0mTJ0NAqOms7TMclS1Q931/0BZErBiA=; b=VGYFpZemiFSpWFvVPoJN8vUGw8Cxc32+nYaCtIwSq97gZtnLyrnpwKHzx1I25M1UFdHWOB YLoGxFvFe02wxHAA== Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id C94CC13888; Tue, 20 May 2025 19:06:00 +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 QDelIZjSLGjVaQAAD6G6ig (envelope-from ); Tue, 20 May 2025 19:06:00 +0000 From: Fabiano Rosas To: Yanfei Xu , peterx@redhat.com Cc: qemu-devel@nongnu.org, Yanfei Xu Subject: Re: [RFC PATCH] migration/ram: avoid to do log clear in the last round In-Reply-To: <20250514115827.3216082-1-yanfei.xu@bytedance.com> References: <20250514115827.3216082-1-yanfei.xu@bytedance.com> Date: Tue, 20 May 2025 16:05:57 -0300 Message-ID: <87zff75ch6.fsf@suse.de> MIME-Version: 1.0 Content-Type: text/plain X-Spamd-Result: default: False [-4.51 / 50.00]; BAYES_HAM(-3.00)[99.99%]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; MISSING_XM_UA(0.00)[]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; TO_DN_SOME(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_TLS_ALL(0.00)[]; RCPT_COUNT_THREE(0.00)[4]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; FUZZY_BLOCKED(0.00)[rspamd.com]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:mid,suse.de:email,suse.de:dkim,imap1.dmz-prg2.suse.org:rdns,imap1.dmz-prg2.suse.org:helo]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; DKIM_TRACE(0.00)[suse.de:+] X-Rspamd-Action: no action X-Rspamd-Server: rspamd1.dmz-prg2.suse.org X-Rspamd-Queue-Id: 5DE251F7DF Received-SPF: pass client-ip=2a07:de40:b251:101:10:150:64:2; 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, 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 Yanfei Xu writes: > There won't be any ram sync after the stage of save_complete, therefore > it's unnecessary to do manually protect for dirty pages being sent. Skip > to do this in last round can reduce noticeable downtime. > > Signed-off-by: Yanfei Xu > --- > As I don't have proper machine to test this patch in qemu and verify if it has > risks like in postcopy, colo and so on.(But I tested this idea on my rust VMM, > it works and can reduce ~50ms for a 128GB guest). So I raise the patch with RFC > for suggestions. > > migration/ram.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/migration/ram.c b/migration/ram.c > index e12913b43e..2b169cdd18 100644 > --- a/migration/ram.c > +++ b/migration/ram.c > @@ -838,7 +838,9 @@ static inline bool migration_bitmap_clear_dirty(RAMState *rs, > * the page in the chunk we clear the remote dirty bitmap for all. > * Clearing it earlier won't be a problem, but too late will. > */ > - migration_clear_memory_region_dirty_bitmap(rb, page); > + if (!rs->last_stage) { > + migration_clear_memory_region_dirty_bitmap(rb, page); > + } > > ret = test_and_clear_bit(page, rb->bmap); > if (ret) { Well, it looks ok to me and passes all my tests. Tested-by: Fabiano Rosas Reviewed-by: Fabiano Rosas