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Tue, 28 May 2024 18:16:09 +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 96j1MGkfVmYlfQAAD6G6ig (envelope-from ); Tue, 28 May 2024 18:16:09 +0000 From: Fabiano Rosas To: Peter Xu , Nicholas Piggin Cc: qemu-devel@nongnu.org, Thomas Huth , Laurent Vivier , Paolo Bonzini , qemu-ppc@nongnu.org Subject: Re: [PATCH] tests/qtest/migrate-test: Use regular file file for shared-memory tests In-Reply-To: References: <20240528042758.621589-1-npiggin@gmail.com> Date: Tue, 28 May 2024 15:16:07 -0300 Message-ID: <87jzjdg5ug.fsf@suse.de> MIME-Version: 1.0 Content-Type: text/plain X-Spamd-Result: default: False [-6.51 / 50.00]; BAYES_HAM(-3.00)[100.00%]; DWL_DNSWL_MED(-2.00)[suse.de:dkim]; 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)[]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FREEMAIL_TO(0.00)[redhat.com,gmail.com]; ARC_NA(0.00)[]; FUZZY_BLOCKED(0.00)[rspamd.com]; MIME_TRACE(0.00)[0:+]; SPAMHAUS_XBL(0.00)[2a07:de40:b281:104:10:150:64:97:from]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_TLS_ALL(0.00)[]; DKIM_TRACE(0.00)[suse.de:+]; RCVD_COUNT_TWO(0.00)[2]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; RCPT_COUNT_SEVEN(0.00)[7]; MISSING_XM_UA(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:dkim, imap1.dmz-prg2.suse.org:helo, imap1.dmz-prg2.suse.org:rdns] X-Rspamd-Action: no action X-Rspamd-Queue-Id: 84579203D4 X-Rspamd-Server: rspamd1.dmz-prg2.suse.org 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, 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 Peter Xu writes: > On Tue, May 28, 2024 at 09:35:22AM -0400, Peter Xu wrote: >> On Tue, May 28, 2024 at 02:27:57PM +1000, Nicholas Piggin wrote: >> > There is no need to use /dev/shm for file-backed memory devices, and >> > it is too small to be usable in gitlab CI. Switch to using a regular >> > file in /tmp/ which will usually have more space available. >> > >> > Signed-off-by: Nicholas Piggin >> > --- >> > Am I missing something? AFAIKS there is not even any point using >> > /dev/shm aka tmpfs anyway, there is not much special about it as a >> > filesystem. This applies on top of the series just sent, and passes >> > gitlab CI qtests including aarch64. >> >> I think it's just that /dev/shm guarantees shmem usage, while the var >> "tmpfs" implies g_dir_make_tmp() which may be another non-ram based file >> system, while that'll be slightly different comparing to what a real user >> would use - we don't suggest user to put guest RAM on things like btrfs. >> >> One real implication is if we add a postcopy test it'll fail with >> g_dir_make_tmp() when it is not pointing to a shmem mount, as >> UFFDIO_REGISTER will fail there. But that test doesn't yet exist as the >> QEMU paths should be the same even if Linux will trigger different paths >> when different types of mem is used (anonymous v.s. shmem). >> >> If the goal here is to properly handle the case where tmpfs doesn't have >> enough space, how about what I suggested in the other email? >> >> https://lore.kernel.org/r/ZlSppKDE6wzjCF--@x1n >> >> IOW, try populate the shmem region before starting the guest, skip if >> population failed. Would that work? > > Let me append some more info here.. > > I think madvise() isn't needed as fallocate() should do the population work > already, afaiu, then it means we pass the shmem path to QEMU and QEMU > should notice this memory-backend-file existed, open() directly. > > I quicked walk the QEMU memory code and so far it looks all applicable, so > that QEMU should just start the guest with the pre-populated shmem page > caches. > > There's one trick where qemu_ram_mmap() will map some extra pages, on x86 > 4k, and I don't yet know why we did that.. > > /* > * Note: this always allocates at least one extra page of virtual address > * space, even if size is already aligned. > */ > total = size + align; At the end of the function: /* * Leave a single PROT_NONE page allocated after the RAM block, to serve as * a guard page guarding against potential buffer overflows. */