On Thu, Feb 22, 2024 at 6:21 PM Peter Xu <pet...@redhat.com> wrote:
>
> On Wed, Feb 21, 2024 at 06:04:10PM -0300, Fabiano Rosas wrote:
> > Hao Xiang <hao.xi...@bytedance.com> writes:
> >
> > > 1. Implements the zero page detection and handling on the multifd
> > > threads for non-compression, zlib and zstd compression backends.
> > > 2. Added a new value 'multifd' in ZeroPageDetection enumeration.
> > > 3. Add proper asserts to ensure pages->normal are used for normal pages
> > > in all scenarios.
> > >
> > > Signed-off-by: Hao Xiang <hao.xi...@bytedance.com>
> > > ---
> > > migration/meson.build | 1 +
> > > migration/multifd-zero-page.c | 59 +++++++++++++++++++++++++++++++++++
> > > migration/multifd-zlib.c | 26 ++++++++++++---
> > > migration/multifd-zstd.c | 25 ++++++++++++---
> > > migration/multifd.c | 50 +++++++++++++++++++++++------
> > > migration/multifd.h | 7 +++++
> > > qapi/migration.json | 4 ++-
> > > 7 files changed, 151 insertions(+), 21 deletions(-)
> > > create mode 100644 migration/multifd-zero-page.c
> > >
> > > diff --git a/migration/meson.build b/migration/meson.build
> > > index 92b1cc4297..1eeb915ff6 100644
> > > --- a/migration/meson.build
> > > +++ b/migration/meson.build
> > > @@ -22,6 +22,7 @@ system_ss.add(files(
> > > 'migration.c',
> > > 'multifd.c',
> > > 'multifd-zlib.c',
> > > + 'multifd-zero-page.c',
> > > 'ram-compress.c',
> > > 'options.c',
> > > 'postcopy-ram.c',
> > > diff --git a/migration/multifd-zero-page.c b/migration/multifd-zero-page.c
> > > new file mode 100644
> > > index 0000000000..f0cd8e2c53
> > > --- /dev/null
> > > +++ b/migration/multifd-zero-page.c
> > > @@ -0,0 +1,59 @@
> > > +/*
> > > + * Multifd zero page detection implementation.
> > > + *
> > > + * Copyright (c) 2024 Bytedance Inc
> > > + *
> > > + * Authors:
> > > + * Hao Xiang <hao.xi...@bytedance.com>
> > > + *
> > > + * This work is licensed under the terms of the GNU GPL, version 2 or
> > > later.
> > > + * See the COPYING file in the top-level directory.
> > > + */
> > > +
> > > +#include "qemu/osdep.h"
> > > +#include "qemu/cutils.h"
> > > +#include "exec/ramblock.h"
> > > +#include "migration.h"
> > > +#include "multifd.h"
> > > +#include "options.h"
> > > +#include "ram.h"
> > > +
> > > +void multifd_zero_page_check_send(MultiFDSendParams *p)
> > > +{
> > > + /*
> > > + * QEMU older than 9.0 don't understand zero page
> > > + * on multifd channel. This switch is required to
> > > + * maintain backward compatibility.
> > > + */
> > > + bool use_multifd_zero_page =
> > > + (migrate_zero_page_detection() == ZERO_PAGE_DETECTION_MULTIFD);
> > > + MultiFDPages_t *pages = p->pages;
> > > + RAMBlock *rb = pages->block;
> > > +
> > > + assert(pages->num != 0);
> > > + assert(pages->normal_num == 0);
> > > + assert(pages->zero_num == 0);
> >
> > We can drop these before the final version.
> >
> > > +
> > > + for (int i = 0; i < pages->num; i++) {
> > > + uint64_t offset = pages->offset[i];
> > > + if (use_multifd_zero_page &&
> > > + buffer_is_zero(rb->host + offset, p->page_size)) {
> > > + pages->zero[pages->zero_num] = offset;
> > > + pages->zero_num++;
> > > + ram_release_page(rb->idstr, offset);
> > > + } else {
> > > + pages->normal[pages->normal_num] = offset;
> > > + pages->normal_num++;
> > > + }
> > > + }
> >
> > I don't think it's super clean to have three arrays offset, zero and
> > normal, all sized for the full packet size. It might be possible to just
> > carry a bitmap of non-zero pages along with pages->offset and operate on
> > that instead.
> >
> > What do you think?
> >
> > Peter, any ideas? Should we just leave this for another time?
>
> Yeah I think a bitmap should save quite a few fields indeed, it'll however
> make the latter iteration slightly harder by walking both (offset[],
> bitmap), process the page only if bitmap is set for the offset.
>
> IIUC we perhaps don't even need a bitmap? AFAIU what we only need in
> Multifdpages_t is one extra field to mark "how many normal pages", aka,
> normal_num here (zero_num can be calculated from num-normal_num). Then
> the zero page detection logic should do two things:
>
> - Sort offset[] array so that it starts with normal pages, followed up by
> zero pages
>
> - Setup normal_num to be the number of normal pages
>
> Then we reduce 2 new arrays (normal[], zero[]) + 2 new fields (normal_num,
> zero_num) -> 1 new field (normal_num). It'll also be trivial to fill the
> packet header later because offset[] is exactly that.
>
> Side note - I still think it's confusing to read this patch and previous
> patch separately. Obviously previous patch introduced these new fields
> without justifying their values yet. IMHO it'll be easier to review if you
> merge the two patches.
Fabiano, thanks for catching this. I totally missed the backward
compatibility thing.
Peter, I will code the sorting and merge this patch with the previous one.
>
> >
> > > +}
> > > +
> > > +void multifd_zero_page_check_recv(MultiFDRecvParams *p)
> > > +{
> > > + for (int i = 0; i < p->zero_num; i++) {
> > > + void *page = p->host + p->zero[i];
> > > + if (!buffer_is_zero(page, p->page_size)) {
> > > + memset(page, 0, p->page_size);
> > > + }
> > > + }
> > > +}
> > > diff --git a/migration/multifd-zlib.c b/migration/multifd-zlib.c
> > > index 012e3bdea1..cdfe0fa70e 100644
> > > --- a/migration/multifd-zlib.c
> > > +++ b/migration/multifd-zlib.c
> > > @@ -123,13 +123,20 @@ static int zlib_send_prepare(MultiFDSendParams *p,
> > > Error **errp)
> > > int ret;
> > > uint32_t i;
> > >
> > > + multifd_zero_page_check_send(p);
> > > +
> > > + if (!pages->normal_num) {
> > > + p->next_packet_size = 0;
> > > + goto out;
> > > + }
> > > +
> > > multifd_send_prepare_header(p);
> > >
> > > - for (i = 0; i < pages->num; i++) {
> > > + for (i = 0; i < pages->normal_num; i++) {
> > > uint32_t available = z->zbuff_len - out_size;
> > > int flush = Z_NO_FLUSH;
> > >
> > > - if (i == pages->num - 1) {
> > > + if (i == pages->normal_num - 1) {
> > > flush = Z_SYNC_FLUSH;
> > > }
> > >
> > > @@ -138,7 +145,7 @@ static int zlib_send_prepare(MultiFDSendParams *p,
> > > Error **errp)
> > > * with compression. zlib does not guarantee that this is safe,
> > > * therefore copy the page before calling deflate().
> > > */
> > > - memcpy(z->buf, p->pages->block->host + pages->offset[i],
> > > p->page_size);
> > > + memcpy(z->buf, p->pages->block->host + pages->normal[i],
> > > p->page_size);
> > > zs->avail_in = p->page_size;
> > > zs->next_in = z->buf;
> > >
> > > @@ -172,10 +179,10 @@ static int zlib_send_prepare(MultiFDSendParams *p,
> > > Error **errp)
> > > p->iov[p->iovs_num].iov_len = out_size;
> > > p->iovs_num++;
> > > p->next_packet_size = out_size;
> > > - p->flags |= MULTIFD_FLAG_ZLIB;
> > >
> > > +out:
> > > + p->flags |= MULTIFD_FLAG_ZLIB;
> > > multifd_send_fill_packet(p);
> > > -
> > > return 0;
> > > }
> > >
> > > @@ -261,6 +268,14 @@ static int zlib_recv_pages(MultiFDRecvParams *p,
> > > Error **errp)
> > > p->id, flags, MULTIFD_FLAG_ZLIB);
> > > return -1;
> > > }
> > > +
> > > + multifd_zero_page_check_recv(p);
> > > +
> > > + if (!p->normal_num) {
> > > + assert(in_size == 0);
> > > + return 0;
> > > + }
> > > +
> > > ret = qio_channel_read_all(p->c, (void *)z->zbuff, in_size, errp);
> > >
> > > if (ret != 0) {
> > > @@ -310,6 +325,7 @@ static int zlib_recv_pages(MultiFDRecvParams *p,
> > > Error **errp)
> > > p->id, out_size, expected_size);
> > > return -1;
> > > }
> > > +
> > > return 0;
> > > }
> > >
> > > diff --git a/migration/multifd-zstd.c b/migration/multifd-zstd.c
> > > index dc8fe43e94..27a1eba075 100644
> > > --- a/migration/multifd-zstd.c
> > > +++ b/migration/multifd-zstd.c
> > > @@ -118,19 +118,26 @@ static int zstd_send_prepare(MultiFDSendParams *p,
> > > Error **errp)
> > > int ret;
> > > uint32_t i;
> > >
> > > + multifd_zero_page_check_send(p);
> > > +
> > > + if (!pages->normal_num) {
> > > + p->next_packet_size = 0;
> > > + goto out;
> > > + }
> > > +
> > > multifd_send_prepare_header(p);
>
> If this forms a pattern we can introduce multifd_send_prepare_common():
I will add that in the next version.
>
> bool multifd_send_prepare_common()
> {
> multifd_zero_page_check_send();
> if (...) {
>
> }
> multifd_send_prepare_header();
> }
>
> > >
> > > z->out.dst = z->zbuff;
> > > z->out.size = z->zbuff_len;
> > > z->out.pos = 0;
> > >
> > > - for (i = 0; i < pages->num; i++) {
> > > + for (i = 0; i < pages->normal_num; i++) {
> > > ZSTD_EndDirective flush = ZSTD_e_continue;
> > >
> > > - if (i == pages->num - 1) {
> > > + if (i == pages->normal_num - 1) {
> > > flush = ZSTD_e_flush;
> > > }
> > > - z->in.src = p->pages->block->host + pages->offset[i];
> > > + z->in.src = p->pages->block->host + pages->normal[i];
> > > z->in.size = p->page_size;
> > > z->in.pos = 0;
> > >
> > > @@ -161,10 +168,10 @@ static int zstd_send_prepare(MultiFDSendParams *p,
> > > Error **errp)
> > > p->iov[p->iovs_num].iov_len = z->out.pos;
> > > p->iovs_num++;
> > > p->next_packet_size = z->out.pos;
> > > - p->flags |= MULTIFD_FLAG_ZSTD;
> > >
> > > +out:
> > > + p->flags |= MULTIFD_FLAG_ZSTD;
> > > multifd_send_fill_packet(p);
> > > -
> > > return 0;
> > > }
> > >
> > > @@ -257,6 +264,14 @@ static int zstd_recv_pages(MultiFDRecvParams *p,
> > > Error **errp)
> > > p->id, flags, MULTIFD_FLAG_ZSTD);
> > > return -1;
> > > }
> > > +
> > > + multifd_zero_page_check_recv(p);
> > > +
> > > + if (!p->normal_num) {
> > > + assert(in_size == 0);
> > > + return 0;
> > > + }
> > > +
> > > ret = qio_channel_read_all(p->c, (void *)z->zbuff, in_size, errp);
> > >
> > > if (ret != 0) {
> > > diff --git a/migration/multifd.c b/migration/multifd.c
> > > index a33dba40d9..fbb40ea10b 100644
> > > --- a/migration/multifd.c
> > > +++ b/migration/multifd.c
> > > @@ -11,6 +11,7 @@
> > > */
> > >
> > > #include "qemu/osdep.h"
> > > +#include "qemu/cutils.h"
> > > #include "qemu/rcu.h"
> > > #include "exec/target_page.h"
> > > #include "sysemu/sysemu.h"
> > > @@ -126,6 +127,8 @@ static int nocomp_send_prepare(MultiFDSendParams *p,
> > > Error **errp)
> > > MultiFDPages_t *pages = p->pages;
> > > int ret;
> > >
> > > + multifd_zero_page_check_send(p);
> > > +
> > > if (!use_zero_copy_send) {
> > > /*
> > > * Only !zerocopy needs the header in IOV; zerocopy will
> > > @@ -134,13 +137,13 @@ static int nocomp_send_prepare(MultiFDSendParams
> > > *p, Error **errp)
> > > multifd_send_prepare_header(p);
> > > }
> > >
> > > - for (int i = 0; i < pages->num; i++) {
> > > - p->iov[p->iovs_num].iov_base = pages->block->host +
> > > pages->offset[i];
> > > + for (int i = 0; i < pages->normal_num; i++) {
> > > + p->iov[p->iovs_num].iov_base = pages->block->host +
> > > pages->normal[i];
> > > p->iov[p->iovs_num].iov_len = p->page_size;
> > > p->iovs_num++;
> > > }
> > >
> > > - p->next_packet_size = pages->num * p->page_size;
> > > + p->next_packet_size = pages->normal_num * p->page_size;
> > > p->flags |= MULTIFD_FLAG_NOCOMP;
> > >
> > > multifd_send_fill_packet(p);
> > > @@ -202,6 +205,13 @@ static int nocomp_recv_pages(MultiFDRecvParams *p,
> > > Error **errp)
> > > p->id, flags, MULTIFD_FLAG_NOCOMP);
> > > return -1;
> > > }
> > > +
> > > + multifd_zero_page_check_recv(p);
> > > +
> > > + if (!p->normal_num) {
> > > + return 0;
> > > + }
> > > +
> > > for (int i = 0; i < p->normal_num; i++) {
> > > p->iov[i].iov_base = p->host + p->normal[i];
> > > p->iov[i].iov_len = p->page_size;
> > > @@ -339,7 +349,7 @@ void multifd_send_fill_packet(MultiFDSendParams *p)
> > >
> > > packet->flags = cpu_to_be32(p->flags);
> > > packet->pages_alloc = cpu_to_be32(p->pages->allocated);
> > > - packet->normal_pages = cpu_to_be32(pages->num);
> > > + packet->normal_pages = cpu_to_be32(pages->normal_num);
> > > packet->zero_pages = cpu_to_be32(pages->zero_num);
> > > packet->next_packet_size = cpu_to_be32(p->next_packet_size);
> > >
> > > @@ -350,18 +360,25 @@ void multifd_send_fill_packet(MultiFDSendParams *p)
> > > strncpy(packet->ramblock, pages->block->idstr, 256);
> > > }
> > >
> > > - for (i = 0; i < pages->num; i++) {
> > > + for (i = 0; i < pages->normal_num; i++) {
> > > /* there are architectures where ram_addr_t is 32 bit */
> > > - uint64_t temp = pages->offset[i];
> > > + uint64_t temp = pages->normal[i];
> > >
> > > packet->offset[i] = cpu_to_be64(temp);
> > > }
> > >
> > > + for (i = 0; i < pages->zero_num; i++) {
> > > + /* there are architectures where ram_addr_t is 32 bit */
> > > + uint64_t temp = pages->zero[i];
> > > +
> > > + packet->offset[pages->normal_num + i] = cpu_to_be64(temp);
> > > + }
> > > +
> > > p->packets_sent++;
> > > - p->total_normal_pages += pages->num;
> > > + p->total_normal_pages += pages->normal_num;
> > > p->total_zero_pages += pages->zero_num;
> > >
> > > - trace_multifd_send(p->id, packet_num, pages->num, pages->zero_num,
> > > + trace_multifd_send(p->id, packet_num, pages->normal_num,
> > > pages->zero_num,
> > > p->flags, p->next_packet_size);
> > > }
> > >
> > > @@ -451,6 +468,18 @@ static int
> > > multifd_recv_unfill_packet(MultiFDRecvParams *p, Error **errp)
> > > p->normal[i] = offset;
> > > }
> > >
> > > + for (i = 0; i < p->zero_num; i++) {
> > > + uint64_t offset = be64_to_cpu(packet->offset[p->normal_num + i]);
> > > +
> > > + if (offset > (p->block->used_length - p->page_size)) {
> > > + error_setg(errp, "multifd: offset too long %" PRIu64
> > > + " (max " RAM_ADDR_FMT ")",
> > > + offset, p->block->used_length);
> > > + return -1;
> > > + }
> > > + p->zero[i] = offset;
> > > + }
> > > +
> > > return 0;
> > > }
> > >
> > > @@ -842,7 +871,7 @@ static void *multifd_send_thread(void *opaque)
> > >
> > > stat64_add(&mig_stats.multifd_bytes,
> > > p->next_packet_size + p->packet_len);
> > > - stat64_add(&mig_stats.normal_pages, pages->num);
> > > + stat64_add(&mig_stats.normal_pages, pages->normal_num);
> > > stat64_add(&mig_stats.zero_pages, pages->zero_num);
> > >
> > > multifd_pages_reset(p->pages);
> > > @@ -1256,7 +1285,8 @@ static void *multifd_recv_thread(void *opaque)
> > > p->flags &= ~MULTIFD_FLAG_SYNC;
> > > qemu_mutex_unlock(&p->mutex);
> > >
> > > - if (p->normal_num) {
> > > + if (p->normal_num + p->zero_num) {
> > > + assert(!(flags & MULTIFD_FLAG_SYNC));
> >
> > This breaks 8.2 -> 9.0 migration. QEMU 8.2 is still sending the SYNC
> > along with the data packet.
> >
> > > ret = multifd_recv_state->ops->recv_pages(p, &local_err);
> > > if (ret != 0) {
> > > break;
> > > diff --git a/migration/multifd.h b/migration/multifd.h
> > > index 9822ff298a..125f0bbe60 100644
> > > --- a/migration/multifd.h
> > > +++ b/migration/multifd.h
> > > @@ -53,6 +53,11 @@ typedef struct {
> > > uint32_t unused32[1]; /* Reserved for future use */
> > > uint64_t unused64[3]; /* Reserved for future use */
> > > char ramblock[256];
> > > + /*
> > > + * This array contains the pointers to:
> > > + * - normal pages (initial normal_pages entries)
> > > + * - zero pages (following zero_pages entries)
> > > + */
> > > uint64_t offset[];
> > > } __attribute__((packed)) MultiFDPacket_t;
> > >
> > > @@ -224,6 +229,8 @@ typedef struct {
> > >
> > > void multifd_register_ops(int method, MultiFDMethods *ops);
> > > void multifd_send_fill_packet(MultiFDSendParams *p);
> > > +void multifd_zero_page_check_send(MultiFDSendParams *p);
> > > +void multifd_zero_page_check_recv(MultiFDRecvParams *p);
> > >
> > > static inline void multifd_send_prepare_header(MultiFDSendParams *p)
> > > {
> > > diff --git a/qapi/migration.json b/qapi/migration.json
> > > index 99843a8e95..e2450b92d4 100644
> > > --- a/qapi/migration.json
> > > +++ b/qapi/migration.json
> > > @@ -660,9 +660,11 @@
> > > #
> > > # @none: Do not perform zero page checking.
> > > #
> > > +# @multifd: Perform zero page checking on the multifd sender thread.
> > > (since 9.0)
> > > +#
> > > ##
> > > { 'enum': 'ZeroPageDetection',
> > > - 'data': [ 'legacy', 'none' ] }
> > > + 'data': [ 'legacy', 'none', 'multifd' ] }
> > >
> > > ##
> > > # @BitmapMigrationBitmapAliasTransform:
> >
>
> --
> Peter Xu
>
