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Tue, 25 Jan 2022 01:42:37 -0800 (PST) Received: from localhost ([47.61.17.76]) by smtp.gmail.com with ESMTPSA id u15sm4649810wrs.17.2022.01.25.01.42.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 25 Jan 2022 01:42:37 -0800 (PST) From: Juan Quintela To: "Dr. David Alan Gilbert" Subject: Re: [PATCH v4 21/23] multifd: Zero pages transmission In-Reply-To: (David Alan Gilbert's message of "Tue, 18 Jan 2022 19:55:35 +0000") References: <20220111130024.5392-1-quintela@redhat.com> <20220111130024.5392-22-quintela@redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) Date: Tue, 25 Jan 2022 10:42:36 +0100 Message-ID: <87h79srw1f.fsf@secure.mitica> MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=quintela@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Received-SPF: pass client-ip=170.10.133.124; envelope-from=quintela@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.158, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=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: , Reply-To: quintela@redhat.com Cc: Eduardo Habkost , qemu-devel@nongnu.org, Peter Xu , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , Yanan Wang , Leonardo Bras Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" "Dr. David Alan Gilbert" wrote: > * Juan Quintela (quintela@redhat.com) wrote: >> This implements the zero page dection and handling. >> >> Signed-off-by: Juan Quintela >> >> --- >> >> Add comment for offset (dave) >> } >> } >> >> + for (int i = 0; i < p->zero_num; i++) { >> + memset(p->host + p->zero[i], 0, qemu_target_page_size()); >> + } >> + > > On the existing code, it tries to avoid doing the memset if the target > page size matches; that avoids allocating the zero pages on the > destination host; should we try and do the same here? > > Dave Hi Dave That only happens on postcopy. With precopy we have to do the memset, because we can have: write non zero to page 50 migrate page 50 write zeros to page 50 Another migration pass If we don't write here, we have garbage on the page. Or I am missing something? Later, Juan.