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[99.254.144.39]) by smtp.gmail.com with ESMTPSA id x19-20020a05622a001300b0041e211c5d0bsm649988qtw.6.2023.10.31.09.52.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 31 Oct 2023 09:52:54 -0700 (PDT) Date: Tue, 31 Oct 2023 12:52:52 -0400 From: Peter Xu To: Fabiano Rosas 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: [PATCH v2 15/29] migration/ram: Add support for 'fixed-ram' outgoing migration Message-ID: References: <20231023203608.26370-1-farosas@suse.de> <20231023203608.26370-16-farosas@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20231023203608.26370-16-farosas@suse.de> Received-SPF: pass client-ip=170.10.129.124; envelope-from=peterx@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -25 X-Spam_score: -2.6 X-Spam_bar: -- X-Spam_report: (-2.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.481, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, 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 On Mon, Oct 23, 2023 at 05:35:54PM -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): > > ramblock 1 header|ramblock 2 header|...|RAM_SAVE_FLAG_EOS|stream of > pages (iter 1)|RAM_SAVE_FLAG_EOS|stream of pages (iter 2)|... > > With fixed-ram (new): > > ramblock 1 header|ramblock 1 fixed-ram header|ramblock 1 pages (fixed > offsets)|ramblock 2 header|ramblock 2 fixed-ram header|ramblock 2 > pages (fixed offsets)|...|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 > --- > include/exec/ramblock.h | 8 ++++ > migration/options.c | 3 -- > migration/ram.c | 98 ++++++++++++++++++++++++++++++++++++----- > 3 files changed, 96 insertions(+), 13 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; > + /* > + * 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; > /* bitmap of already received pages in postcopy */ > unsigned long *receivedmap; > > diff --git a/migration/options.c b/migration/options.c > index 2622d8c483..9f693d909f 100644 > --- a/migration/options.c > +++ b/migration/options.c > @@ -271,12 +271,9 @@ bool migrate_events(void) > > bool migrate_fixed_ram(void) > { > -/* > MigrationState *s = migrate_get_current(); > > return s->capabilities[MIGRATION_CAPABILITY_FIXED_RAM]; > -*/ > - return false; > } > > bool migrate_ignore_shared(void) > diff --git a/migration/ram.c b/migration/ram.c > index 92769902bb..152a03604f 100644 > --- a/migration/ram.c > +++ b/migration/ram.c > @@ -1157,12 +1157,18 @@ static int save_zero_page(RAMState *rs, PageSearchStatus *pss, > return 0; > } > > + stat64_add(&mig_stats.zero_pages, 1); Here we keep zero page accounting, but.. > + > + 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); > > /* > @@ -1220,14 +1226,20 @@ 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)); .. here we ignored normal page accounting. I think we should have the same behavior on both, perhaps keep them always? > + 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); > @@ -2475,6 +2487,8 @@ 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(); > @@ -2842,6 +2856,7 @@ static void ram_list_init_bitmaps(void) > */ > block->bmap = bitmap_new(pages); > bitmap_set(block->bmap, 0, pages); > + block->shadow_bmap = bitmap_new(block->used_length >> TARGET_PAGE_BITS); AFAICT bmap should also use used_length. How about adding one more patch to change that, then you can use "pages" here? See ram_mig_ram_block_resized() where we call migration_cancel() if resized. > block->clear_bmap_shift = shift; > block->clear_bmap = bitmap_new(clear_bmap_size(pages, shift)); > } > @@ -2979,6 +2994,44 @@ void qemu_guest_free_page_hint(void *addr, size_t len) > } > } > > +#define FIXED_RAM_HDR_VERSION 1 > +struct FixedRamHeader { > + uint32_t version; > + uint64_t page_size; > + uint64_t bitmap_offset; > + uint64_t pages_offset; > + /* end of v1 */ > +} QEMU_PACKED; > + > +static void fixed_ram_insert_header(QEMUFile *file, RAMBlock *block) > +{ > + g_autofree struct FixedRamHeader *header; > + size_t header_size, bitmap_size; > + long num_pages; > + > + header = g_new0(struct FixedRamHeader, 1); > + header_size = sizeof(struct 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, 0x100000); > + > + header->version = cpu_to_be32(FIXED_RAM_HDR_VERSION); > + header->page_size = cpu_to_be64(TARGET_PAGE_SIZE); This is the "page size" for the shadow bitmap, right? Shall we state it somewhere (e.g. explaining why it's not block->page_size)? It's unfortunate that we already have things like: if (migrate_postcopy_ram() && block->page_size != qemu_host_page_size) { qemu_put_be64(f, block->page_size); } But indeed we can't merge them because they seem to service different purpose. > + 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 > @@ -3028,6 +3081,12 @@ 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); > + } > } > } > > @@ -3061,6 +3120,20 @@ static int ram_save_setup(QEMUFile *f, void *opaque) > return 0; > } > > +static void ram_save_shadow_bmap(QEMUFile *f) > +{ > + 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); > + /* to catch any thread late sending pages */ > + block->shadow_bmap = NULL; What is this for? Wouldn't this leak the buffer already? > + } > +} > + > /** > * ram_save_iterate: iterative stage for migration > * > @@ -3179,7 +3252,6 @@ out: > qemu_put_be64(f, RAM_SAVE_FLAG_EOS); > qemu_fflush(f); > ram_transferred_add(8); > - > ret = qemu_file_get_error(f); > } > if (ret < 0) { > @@ -3256,7 +3328,13 @@ static int ram_save_complete(QEMUFile *f, void *opaque) > if (migrate_multifd() && !migrate_multifd_flush_after_each_section()) { > qemu_put_be64(f, RAM_SAVE_FLAG_MULTIFD_FLUSH); > } > + > + if (migrate_fixed_ram()) { > + ram_save_shadow_bmap(f); > + } > + > qemu_put_be64(f, RAM_SAVE_FLAG_EOS); > + > qemu_fflush(f); > > return 0; > -- > 2.35.3 > -- Peter Xu