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Mon, 15 Jan 2024 14:50:05 +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 zC9gMx1GpWVvegAAD6G6ig (envelope-from ); Mon, 15 Jan 2024 14:50:05 +0000 From: Fabiano Rosas To: Peter Xu Cc: qemu-devel@nongnu.org, berrange@redhat.com, armbru@redhat.com, Juan Quintela , Leonardo Bras , Claudio Fontana , Nikolay Borisov , Paolo Bonzini , David Hildenbrand , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= Subject: Re: [RFC PATCH v3 08/30] migration/ram: Add outgoing 'fixed-ram' migration In-Reply-To: References: <20231127202612.23012-1-farosas@suse.de> <20231127202612.23012-9-farosas@suse.de> Date: Mon, 15 Jan 2024 11:50:03 -0300 Message-ID: <878r4q6484.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=JVTGNE1h; dkim=pass header.d=suse.de header.s=susede2_ed25519 header.b=DDRE3lOa 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]; 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)[]; RCPT_COUNT_SEVEN(0.00)[11]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.com:email,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: 9929521F05 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 Peter Xu writes: > On Mon, Nov 27, 2023 at 05:25:50PM -0300, Fabiano Rosas wrote: >> From: Nikolay Borisov >> >> Implement the outgoing migration side for the 'fixed-ram' capability. >> >> A bitmap is introduced to track which pages have been written in the >> migration file. Pages are written at a fixed location for every >> ramblock. Zero pages are ignored as they'd be zero in the destination >> migration as well. >> >> The migration stream is altered to put the dirty pages for a ramblock >> after its header instead of having a sequential stream of pages that >> follow the ramblock headers. Since all pages have a fixed location, >> RAM_SAVE_FLAG_EOS is no longer generated on every migration iteration. >> >> Without fixed-ram (current): With fixed-ram (new): >> >> --------------------- -------------------------------- >> | ramblock 1 header | | ramblock 1 header | >> --------------------- -------------------------------- >> | ramblock 2 header | | ramblock 1 fixed-ram header | >> --------------------- -------------------------------- >> | ... | | padding to next 1MB boundary | >> --------------------- | ... | >> | ramblock n header | -------------------------------- >> --------------------- | ramblock 1 pages | >> | RAM_SAVE_FLAG_EOS | | ... | >> --------------------- -------------------------------- >> | stream of pages | | ramblock 2 header | >> | (iter 1) | -------------------------------- >> | ... | | ramblock 2 fixed-ram header | >> --------------------- -------------------------------- >> | RAM_SAVE_FLAG_EOS | | padding to next 1MB boundary | >> --------------------- | ... | >> | stream of pages | -------------------------------- >> | (iter 2) | | ramblock 2 pages | >> | ... | | ... | >> --------------------- -------------------------------- >> | ... | | ... | >> --------------------- -------------------------------- >> | RAM_SAVE_FLAG_EOS | >> -------------------------------- >> | ... | >> -------------------------------- >> >> where: >> - ramblock header: the generic information for a ramblock, such as >> idstr, used_len, etc. >> >> - ramblock fixed-ram header: the new information added by this >> feature: bitmap of pages written, bitmap size and offset of pages >> in the migration file. >> >> Signed-off-by: Nikolay Borisov >> Signed-off-by: Fabiano Rosas >> --- >> - used a macro for alignment value >> - documented alignment assumptions >> - moved shadow_bmap debug code to multifd patch >> - did NOT use used_length for bmap, it breaks dirty page tracking somehow >> - uncommented the capability enabling >> - accounted for the bitmap size with ram_transferred_add() >> --- >> include/exec/ramblock.h | 8 +++ >> migration/ram.c | 121 +++++++++++++++++++++++++++++++++++++--- >> 2 files changed, 120 insertions(+), 9 deletions(-) >> >> diff --git a/include/exec/ramblock.h b/include/exec/ramblock.h >> index 69c6a53902..e0e3f16852 100644 >> --- a/include/exec/ramblock.h >> +++ b/include/exec/ramblock.h >> @@ -44,6 +44,14 @@ struct RAMBlock { >> size_t page_size; >> /* dirty bitmap used during migration */ >> unsigned long *bmap; >> + /* shadow dirty bitmap used when migrating to a file */ >> + unsigned long *shadow_bmap; > > What is a "shadow dirty bitmap"? It's pretty unclear to me. > > AFAICT it's actually a "page present" bitmap, while taking zero pages as > "not present", no? > Yes, something like that. It's the bitmap of pages written to the migration file. >> + /* >> + * offset in the file pages belonging to this ramblock are saved, >> + * used only during migration to a file. >> + */ >> + off_t bitmap_offset; >> + uint64_t pages_offset; > > Let's have a section to put fixed-ram data? > > /* > * Below fields are only used by fixed-ram migration. > */ > ... > >> /* bitmap of already received pages in postcopy */ >> unsigned long *receivedmap; >> >> diff --git a/migration/ram.c b/migration/ram.c >> index 8c7886ab79..4a0ab8105f 100644 >> --- a/migration/ram.c >> +++ b/migration/ram.c >> @@ -94,6 +94,18 @@ >> #define RAM_SAVE_FLAG_MULTIFD_FLUSH 0x200 >> /* We can't use any flag that is bigger than 0x200 */ >> >> +/* >> + * fixed-ram migration supports O_DIRECT, so we need to make sure the >> + * userspace buffer, the IO operation size and the file offset are >> + * aligned according to the underlying device's block size. The first >> + * two are already aligned to page size, but we need to add padding to >> + * the file to align the offset. We cannot read the block size >> + * dynamically because the migration file can be moved between >> + * different systems, so use 1M to cover most block sizes and to keep >> + * the file offset aligned at page size as well. >> + */ >> +#define FIXED_RAM_FILE_OFFSET_ALIGNMENT 0x100000 >> + >> XBZRLECacheStats xbzrle_counters; >> >> /* used by the search for pages to send */ >> @@ -1127,12 +1139,18 @@ static int save_zero_page(RAMState *rs, PageSearchStatus *pss, >> return 0; >> } >> >> + stat64_add(&mig_stats.zero_pages, 1); >> + >> + if (migrate_fixed_ram()) { >> + /* zero pages are not transferred with fixed-ram */ >> + clear_bit(offset >> TARGET_PAGE_BITS, pss->block->shadow_bmap); >> + return 1; >> + } >> + >> len += save_page_header(pss, file, pss->block, offset | RAM_SAVE_FLAG_ZERO); >> qemu_put_byte(file, 0); >> len += 1; >> ram_release_page(pss->block->idstr, offset); >> - >> - stat64_add(&mig_stats.zero_pages, 1); >> ram_transferred_add(len); >> >> /* >> @@ -1190,14 +1208,20 @@ static int save_normal_page(PageSearchStatus *pss, RAMBlock *block, >> { >> QEMUFile *file = pss->pss_channel; >> >> - ram_transferred_add(save_page_header(pss, pss->pss_channel, block, >> - offset | RAM_SAVE_FLAG_PAGE)); >> - if (async) { >> - qemu_put_buffer_async(file, buf, TARGET_PAGE_SIZE, >> - migrate_release_ram() && >> - migration_in_postcopy()); >> + if (migrate_fixed_ram()) { >> + qemu_put_buffer_at(file, buf, TARGET_PAGE_SIZE, >> + block->pages_offset + offset); >> + set_bit(offset >> TARGET_PAGE_BITS, block->shadow_bmap); >> } else { >> - qemu_put_buffer(file, buf, TARGET_PAGE_SIZE); >> + ram_transferred_add(save_page_header(pss, pss->pss_channel, block, >> + offset | RAM_SAVE_FLAG_PAGE)); >> + if (async) { >> + qemu_put_buffer_async(file, buf, TARGET_PAGE_SIZE, >> + migrate_release_ram() && >> + migration_in_postcopy()); >> + } else { >> + qemu_put_buffer(file, buf, TARGET_PAGE_SIZE); >> + } >> } >> ram_transferred_add(TARGET_PAGE_SIZE); >> stat64_add(&mig_stats.normal_pages, 1); >> @@ -2413,6 +2437,8 @@ static void ram_save_cleanup(void *opaque) >> block->clear_bmap = NULL; >> g_free(block->bmap); >> block->bmap = NULL; >> + g_free(block->shadow_bmap); >> + block->shadow_bmap = NULL; >> } >> >> xbzrle_cleanup(); >> @@ -2780,6 +2806,7 @@ static void ram_list_init_bitmaps(void) >> */ >> block->bmap = bitmap_new(pages); >> bitmap_set(block->bmap, 0, pages); >> + block->shadow_bmap = bitmap_new(pages); > > We can avoid creating this bitmap if !fixed-ram. > ack >> block->clear_bmap_shift = shift; >> block->clear_bmap = bitmap_new(clear_bmap_size(pages, shift)); >> } >> @@ -2917,6 +2944,58 @@ void qemu_guest_free_page_hint(void *addr, size_t len) >> } >> } >> >> +#define FIXED_RAM_HDR_VERSION 1 >> +struct FixedRamHeader { >> + uint32_t version; >> + /* >> + * The target's page size, so we know how many pages are in the >> + * bitmap. >> + */ >> + uint64_t page_size; >> + /* >> + * The offset in the migration file where the pages bitmap is >> + * found. > > s/found/stored/? > >> + */ >> + uint64_t bitmap_offset; >> + /* >> + * The offset in the migration file where the actual pages (data) >> + * are found. > > same? > >> + */ >> + uint64_t pages_offset; >> + /* end of v1 */ > > I think we can drop this. > >> +} QEMU_PACKED; >> +typedef struct FixedRamHeader FixedRamHeader; >> + >> +static void fixed_ram_insert_header(QEMUFile *file, RAMBlock *block) >> +{ >> + g_autofree FixedRamHeader *header; > > Let's either inline the g_new0() or initialize it to NULL? Just in case. Ouch, that's just wrong. I'll fix it. >> + size_t header_size, bitmap_size; >> + long num_pages; >> + >> + header = g_new0(FixedRamHeader, 1); >> + header_size = sizeof(FixedRamHeader); >> + >> + num_pages = block->used_length >> TARGET_PAGE_BITS; >> + bitmap_size = BITS_TO_LONGS(num_pages) * sizeof(unsigned long); >> + >> + /* >> + * Save the file offsets of where the bitmap and the pages should >> + * go as they are written at the end of migration and during the >> + * iterative phase, respectively. >> + */ >> + block->bitmap_offset = qemu_get_offset(file) + header_size; >> + block->pages_offset = ROUND_UP(block->bitmap_offset + >> + bitmap_size, >> + FIXED_RAM_FILE_OFFSET_ALIGNMENT); >> + >> + header->version = cpu_to_be32(FIXED_RAM_HDR_VERSION); >> + header->page_size = cpu_to_be64(TARGET_PAGE_SIZE); >> + header->bitmap_offset = cpu_to_be64(block->bitmap_offset); >> + header->pages_offset = cpu_to_be64(block->pages_offset); >> + >> + qemu_put_buffer(file, (uint8_t *) header, header_size); >> +} >> + >> /* >> * Each of ram_save_setup, ram_save_iterate and ram_save_complete has >> * long-running RCU critical section. When rcu-reclaims in the code >> @@ -2966,6 +3045,13 @@ static int ram_save_setup(QEMUFile *f, void *opaque) >> if (migrate_ignore_shared()) { >> qemu_put_be64(f, block->mr->addr); >> } >> + >> + if (migrate_fixed_ram()) { >> + fixed_ram_insert_header(f, block); >> + /* prepare offset for next ramblock */ >> + qemu_set_offset(f, block->pages_offset + block->used_length, >> + SEEK_SET); > > How about moving this line into fixed_ram_insert_header()? Perhaps also > rename to fixed_ram_setup_ramblock()? > Ok. >> + } >> } >> } >> >> @@ -2999,6 +3085,19 @@ static int ram_save_setup(QEMUFile *f, void *opaque) >> return qemu_fflush(f); >> } >> >> +static void ram_save_shadow_bmap(QEMUFile *f) > > [may need a rename after we decide a better name for the bitmap; "shadow" > is probably not the one..] > >> +{ >> + RAMBlock *block; >> + >> + RAMBLOCK_FOREACH_MIGRATABLE(block) { >> + long num_pages = block->used_length >> TARGET_PAGE_BITS; >> + long bitmap_size = BITS_TO_LONGS(num_pages) * sizeof(unsigned long); >> + qemu_put_buffer_at(f, (uint8_t *)block->shadow_bmap, bitmap_size, >> + block->bitmap_offset); > > We may want to check for IO errors, either here, or (if too frequent) maybe > once and for all right before the final completion of migration? If the > latter, we may want to keep a comment around here explaining on error conditions. > Ok. >> + ram_transferred_add(bitmap_size); >> + } >> +} >> + >> /** >> * ram_save_iterate: iterative stage for migration >> * >> @@ -3188,6 +3287,10 @@ static int ram_save_complete(QEMUFile *f, void *opaque) >> return ret; >> } >> >> + if (migrate_fixed_ram()) { >> + ram_save_shadow_bmap(f); >> + } >> + >> if (migrate_multifd() && !migrate_multifd_flush_after_each_section()) { >> qemu_put_be64(f, RAM_SAVE_FLAG_MULTIFD_FLUSH); >> } >> -- >> 2.35.3 >>