| Message ID | 20180313075739.11194-4-xiaoguangrong@tencent.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
* guangrong.xiao@gmail.com (guangrong.xiao@gmail.com) wrote: > From: Xiao Guangrong <xiaoguangrong@tencent.com> > > Currently the page being compressed is allowed to be updated by > the VM on the source QEMU, correspondingly the destination QEMU > just ignores the decompression error. However, we completely miss > the chance to catch real errors, then the VM is corrupted silently > > To make the migration more robuster, we copy the page to a buffer > first to avoid it being written by VM, then detect and handle the > errors of both compression and decompression errors properly > > Signed-off-by: Xiao Guangrong <xiaoguangrong@tencent.com> > --- > migration/qemu-file.c | 4 ++-- > migration/ram.c | 29 +++++++++++++++++++---------- > 2 files changed, 21 insertions(+), 12 deletions(-) > > diff --git a/migration/qemu-file.c b/migration/qemu-file.c > index 1ff33a1ffb..137bcc8bdc 100644 > --- a/migration/qemu-file.c > +++ b/migration/qemu-file.c > @@ -711,9 +711,9 @@ ssize_t qemu_put_compression_data(QEMUFile *f, z_stream *stream, > blen = qemu_compress_data(stream, f->buf + f->buf_index + sizeof(int32_t), > blen, p, size); > if (blen < 0) { > - error_report("Compress Failed!"); > - return 0; > + return -1; > } > + > qemu_put_be32(f, blen); > if (f->ops->writev_buffer) { > add_to_iovec(f, f->buf + f->buf_index, blen, false); > diff --git a/migration/ram.c b/migration/ram.c > index fff3f31e90..c47185d38c 100644 > --- a/migration/ram.c > +++ b/migration/ram.c > @@ -273,6 +273,7 @@ struct DecompressParam { > bool quit; > QemuMutex mutex; > QemuCond cond; > + QEMUFile *file; > void *des; > uint8_t *compbuf; > int len; > @@ -1051,11 +1052,13 @@ static int do_compress_ram_page(QEMUFile *f, z_stream *stream, RAMBlock *block, > { > RAMState *rs = ram_state; > int bytes_sent, blen; > - uint8_t *p = block->host + (offset & TARGET_PAGE_MASK); > + uint8_t buf[TARGET_PAGE_SIZE], *p; That should be malloc'd somewhere rather than be on the stack; it's a bit big and also there are architectures where TARGET_PAGE_SIZE isn't compile time constant. (Also, please use g_try_malloc rather than g_malloc on larger chunks, since g_try_malloc will return NULL so you can fail nicely; g_malloc is OK for small things that are very unlikely to fail). Other than that, I think the patch is fine. Dave > + p = block->host + (offset & TARGET_PAGE_MASK); > bytes_sent = save_page_header(rs, f, block, offset | > RAM_SAVE_FLAG_COMPRESS_PAGE); > - blen = qemu_put_compression_data(f, stream, p, TARGET_PAGE_SIZE); > + memcpy(buf, p, TARGET_PAGE_SIZE); > + blen = qemu_put_compression_data(f, stream, buf, TARGET_PAGE_SIZE); > if (blen < 0) { > bytes_sent = 0; > qemu_file_set_error(migrate_get_current()->to_dst_file, blen); > @@ -2547,7 +2550,7 @@ static void *do_data_decompress(void *opaque) > DecompressParam *param = opaque; > unsigned long pagesize; > uint8_t *des; > - int len; > + int len, ret; > > qemu_mutex_lock(¶m->mutex); > while (!param->quit) { > @@ -2563,8 +2566,12 @@ static void *do_data_decompress(void *opaque) > * not a problem because the dirty page will be retransferred > * and uncompress() won't break the data in other pages. > */ > - qemu_uncompress(¶m->stream, des, pagesize, > - param->compbuf, len); > + ret = qemu_uncompress(¶m->stream, des, pagesize, > + param->compbuf, len); > + if (ret < 0) { > + error_report("decompress data failed"); > + qemu_file_set_error(param->file, ret); > + } > > qemu_mutex_lock(&decomp_done_lock); > param->done = true; > @@ -2581,12 +2588,12 @@ static void *do_data_decompress(void *opaque) > return NULL; > } > > -static void wait_for_decompress_done(void) > +static int wait_for_decompress_done(QEMUFile *f) > { > int idx, thread_count; > > if (!migrate_use_compression()) { > - return; > + return 0; > } > > thread_count = migrate_decompress_threads(); > @@ -2597,6 +2604,7 @@ static void wait_for_decompress_done(void) > } > } > qemu_mutex_unlock(&decomp_done_lock); > + return qemu_file_get_error(f); > } > > static void compress_threads_load_cleanup(void) > @@ -2635,7 +2643,7 @@ static void compress_threads_load_cleanup(void) > decomp_param = NULL; > } > > -static int compress_threads_load_setup(void) > +static int compress_threads_load_setup(QEMUFile *f) > { > int i, thread_count; > > @@ -2654,6 +2662,7 @@ static int compress_threads_load_setup(void) > } > decomp_param[i].stream.opaque = &decomp_param[i]; > > + decomp_param[i].file = f; > qemu_mutex_init(&decomp_param[i].mutex); > qemu_cond_init(&decomp_param[i].cond); > decomp_param[i].compbuf = g_malloc0(compressBound(TARGET_PAGE_SIZE)); > @@ -2708,7 +2717,7 @@ static void decompress_data_with_multi_threads(QEMUFile *f, > */ > static int ram_load_setup(QEMUFile *f, void *opaque) > { > - if (compress_threads_load_setup()) { > + if (compress_threads_load_setup(f)) { > return -1; > } > > @@ -3063,7 +3072,7 @@ static int ram_load(QEMUFile *f, void *opaque, int version_id) > } > } > > - wait_for_decompress_done(); > + ret |= wait_for_decompress_done(f); > rcu_read_unlock(); > trace_ram_load_complete(ret, seq_iter); > return ret; > -- > 2.14.3 > > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
On 03/15/2018 07:29 PM, Dr. David Alan Gilbert wrote: >> @@ -1051,11 +1052,13 @@ static int do_compress_ram_page(QEMUFile *f, z_stream *stream, RAMBlock *block, >> { >> RAMState *rs = ram_state; >> int bytes_sent, blen; >> - uint8_t *p = block->host + (offset & TARGET_PAGE_MASK); >> + uint8_t buf[TARGET_PAGE_SIZE], *p; > > That should be malloc'd somewhere rather than be on the stack; it's a > bit big and also there are architectures where TARGET_PAGE_SIZE isn't > compile time constant. > Okay, i will allocate a internal buffer for each thread... > (Also, please use g_try_malloc rather than g_malloc on larger chunks, > since g_try_malloc will return NULL so you can fail nicely; g_malloc is > OK for small things that are very unlikely to fail). > > Other than that, I think the patch is fine. Thank you, Dave!
Hi, guangrong > @@ -1051,11 +1052,13 @@ static int do_compress_ram_page(QEMUFile *f, z_stream *stream, RAMBlock *block, > { > RAMState *rs = ram_state; > int bytes_sent, blen; > - uint8_t *p = block->host + (offset & TARGET_PAGE_MASK); > + uint8_t buf[TARGET_PAGE_SIZE], *p; > + p = block->host + (offset & TARGET_PAGE_MASK); > bytes_sent = save_page_header(rs, f, block, offset | > RAM_SAVE_FLAG_COMPRESS_PAGE); > - blen = qemu_put_compression_data(f, stream, p, TARGET_PAGE_SIZE); > + memcpy(buf, p, TARGET_PAGE_SIZE); > + blen = qemu_put_compression_data(f, stream, buf, TARGET_PAGE_SIZE); Memory copy operation for every page to be compressed is not cheap, especially when the page number is huge, and it may be not necessary for pages never updated during migration. Is there any possibility that we can distinguish the real compress/decompress errors from those being caused by source VM updating? Such as the return value of qemu_uncompress(distinguish Z_DATA_ERROR and other error codes returned by inflate())? Jiang Regards,
On 03/19/2018 03:56 PM, jiang.biao2@zte.com.cn wrote: > Hi, guangrong >> @@ -1051,11 +1052,13 @@ static int do_compress_ram_page(QEMUFile *f, z_stream *stream, RAMBlock *block, >> { >> RAMState *rs = ram_state; >> int bytes_sent, blen; >> - uint8_t *p = block->host + (offset & TARGET_PAGE_MASK); >> + uint8_t buf[TARGET_PAGE_SIZE], *p; > >> + p = block->host + (offset & TARGET_PAGE_MASK); >> bytes_sent = save_page_header(rs, f, block, offset | >> RAM_SAVE_FLAG_COMPRESS_PAGE); >> - blen = qemu_put_compression_data(f, stream, p, TARGET_PAGE_SIZE); >> + memcpy(buf, p, TARGET_PAGE_SIZE); >> + blen = qemu_put_compression_data(f, stream, buf, TARGET_PAGE_SIZE); > Memory copy operation for every page to be compressed is not cheap, especially > when the page number is huge, and it may be not necessary for pages never > updated during migration. This is only for 4k page. > Is there any possibility that we can distinguish the real compress/decompress > errors from those being caused by source VM updating? Such as the return > value of qemu_uncompress(distinguish Z_DATA_ERROR and other error codes > returned by inflate())? Unfortunately, no. :(
On Tue, Mar 13, 2018 at 03:57:34PM +0800, guangrong.xiao@gmail.com wrote: > From: Xiao Guangrong <xiaoguangrong@tencent.com> > > Currently the page being compressed is allowed to be updated by > the VM on the source QEMU, correspondingly the destination QEMU > just ignores the decompression error. However, we completely miss > the chance to catch real errors, then the VM is corrupted silently > > To make the migration more robuster, we copy the page to a buffer > first to avoid it being written by VM, then detect and handle the > errors of both compression and decompression errors properly Not sure I missed anything important, but I'll just shoot my thoughts as questions (again)... Actually this is a more general question? Say, even without compression, we can be sending a page that is being modified. However, IMHO we don't need to worry that, since if that page is modified, we'll definitely send that page again, so the new page will replace the old. So on destination side, even if decompress() failed on a page it'll be fine IMHO. Though now we are copying the corrupted buffer. On that point, I fully agree that we should not - maybe we can just drop the page entirely? For non-compress pages, we can't detect that, so we'll copy the page even if corrupted. The special part for compression would be: would the deflate() fail if there is concurrent update to the buffer being compressed? And would that corrupt the whole compression stream, or it would only fail the deflate() call? Thanks, > > Signed-off-by: Xiao Guangrong <xiaoguangrong@tencent.com> > --- > migration/qemu-file.c | 4 ++-- > migration/ram.c | 29 +++++++++++++++++++---------- > 2 files changed, 21 insertions(+), 12 deletions(-) > > diff --git a/migration/qemu-file.c b/migration/qemu-file.c > index 1ff33a1ffb..137bcc8bdc 100644 > --- a/migration/qemu-file.c > +++ b/migration/qemu-file.c > @@ -711,9 +711,9 @@ ssize_t qemu_put_compression_data(QEMUFile *f, z_stream *stream, > blen = qemu_compress_data(stream, f->buf + f->buf_index + sizeof(int32_t), > blen, p, size); > if (blen < 0) { > - error_report("Compress Failed!"); > - return 0; > + return -1; > } > + > qemu_put_be32(f, blen); > if (f->ops->writev_buffer) { > add_to_iovec(f, f->buf + f->buf_index, blen, false); > diff --git a/migration/ram.c b/migration/ram.c > index fff3f31e90..c47185d38c 100644 > --- a/migration/ram.c > +++ b/migration/ram.c > @@ -273,6 +273,7 @@ struct DecompressParam { > bool quit; > QemuMutex mutex; > QemuCond cond; > + QEMUFile *file; > void *des; > uint8_t *compbuf; > int len; > @@ -1051,11 +1052,13 @@ static int do_compress_ram_page(QEMUFile *f, z_stream *stream, RAMBlock *block, > { > RAMState *rs = ram_state; > int bytes_sent, blen; > - uint8_t *p = block->host + (offset & TARGET_PAGE_MASK); > + uint8_t buf[TARGET_PAGE_SIZE], *p; > > + p = block->host + (offset & TARGET_PAGE_MASK); > bytes_sent = save_page_header(rs, f, block, offset | > RAM_SAVE_FLAG_COMPRESS_PAGE); > - blen = qemu_put_compression_data(f, stream, p, TARGET_PAGE_SIZE); > + memcpy(buf, p, TARGET_PAGE_SIZE); > + blen = qemu_put_compression_data(f, stream, buf, TARGET_PAGE_SIZE); > if (blen < 0) { > bytes_sent = 0; > qemu_file_set_error(migrate_get_current()->to_dst_file, blen); > @@ -2547,7 +2550,7 @@ static void *do_data_decompress(void *opaque) > DecompressParam *param = opaque; > unsigned long pagesize; > uint8_t *des; > - int len; > + int len, ret; > > qemu_mutex_lock(¶m->mutex); > while (!param->quit) { > @@ -2563,8 +2566,12 @@ static void *do_data_decompress(void *opaque) > * not a problem because the dirty page will be retransferred > * and uncompress() won't break the data in other pages. > */ > - qemu_uncompress(¶m->stream, des, pagesize, > - param->compbuf, len); > + ret = qemu_uncompress(¶m->stream, des, pagesize, > + param->compbuf, len); > + if (ret < 0) { > + error_report("decompress data failed"); > + qemu_file_set_error(param->file, ret); > + } > > qemu_mutex_lock(&decomp_done_lock); > param->done = true; > @@ -2581,12 +2588,12 @@ static void *do_data_decompress(void *opaque) > return NULL; > } > > -static void wait_for_decompress_done(void) > +static int wait_for_decompress_done(QEMUFile *f) > { > int idx, thread_count; > > if (!migrate_use_compression()) { > - return; > + return 0; > } > > thread_count = migrate_decompress_threads(); > @@ -2597,6 +2604,7 @@ static void wait_for_decompress_done(void) > } > } > qemu_mutex_unlock(&decomp_done_lock); > + return qemu_file_get_error(f); > } > > static void compress_threads_load_cleanup(void) > @@ -2635,7 +2643,7 @@ static void compress_threads_load_cleanup(void) > decomp_param = NULL; > } > > -static int compress_threads_load_setup(void) > +static int compress_threads_load_setup(QEMUFile *f) > { > int i, thread_count; > > @@ -2654,6 +2662,7 @@ static int compress_threads_load_setup(void) > } > decomp_param[i].stream.opaque = &decomp_param[i]; > > + decomp_param[i].file = f; > qemu_mutex_init(&decomp_param[i].mutex); > qemu_cond_init(&decomp_param[i].cond); > decomp_param[i].compbuf = g_malloc0(compressBound(TARGET_PAGE_SIZE)); > @@ -2708,7 +2717,7 @@ static void decompress_data_with_multi_threads(QEMUFile *f, > */ > static int ram_load_setup(QEMUFile *f, void *opaque) > { > - if (compress_threads_load_setup()) { > + if (compress_threads_load_setup(f)) { > return -1; > } > > @@ -3063,7 +3072,7 @@ static int ram_load(QEMUFile *f, void *opaque, int version_id) > } > } > > - wait_for_decompress_done(); > + ret |= wait_for_decompress_done(f); > rcu_read_unlock(); > trace_ram_load_complete(ret, seq_iter); > return ret; > -- > 2.14.3 > >
On 03/21/2018 06:00 PM, Peter Xu wrote: > On Tue, Mar 13, 2018 at 03:57:34PM +0800, guangrong.xiao@gmail.com wrote: >> From: Xiao Guangrong <xiaoguangrong@tencent.com> >> >> Currently the page being compressed is allowed to be updated by >> the VM on the source QEMU, correspondingly the destination QEMU >> just ignores the decompression error. However, we completely miss >> the chance to catch real errors, then the VM is corrupted silently >> >> To make the migration more robuster, we copy the page to a buffer >> first to avoid it being written by VM, then detect and handle the >> errors of both compression and decompression errors properly > > Not sure I missed anything important, but I'll just shoot my thoughts > as questions (again)... > > Actually this is a more general question? Say, even without > compression, we can be sending a page that is being modified. > > However, IMHO we don't need to worry that, since if that page is > modified, we'll definitely send that page again, so the new page will > replace the old. So on destination side, even if decompress() failed > on a page it'll be fine IMHO. Though now we are copying the corrupted > buffer. On that point, I fully agree that we should not - maybe we > can just drop the page entirely? > > For non-compress pages, we can't detect that, so we'll copy the page > even if corrupted. > > The special part for compression would be: would the deflate() fail if > there is concurrent update to the buffer being compressed? And would > that corrupt the whole compression stream, or it would only fail the > deflate() call? It is not the same for normal page and compressed page. For the normal page, the dirty-log mechanism in QEMU and the infrastructure of the network (e.g, TCP) can make sure that the modified memory will be posted to the destination without corruption. However, nothing can guarantee compression/decompression is BUG-free, e,g, consider the case, in the last step, vCPUs & dirty-log are paused and the memory is compressed and posted to destination, if there is any error in compression/decompression, VM dies silently.
On 03/27/2018 03:22 PM, Peter Xu wrote: > On Thu, Mar 22, 2018 at 08:03:53PM +0800, Xiao Guangrong wrote: >> >> >> On 03/21/2018 06:00 PM, Peter Xu wrote: >>> On Tue, Mar 13, 2018 at 03:57:34PM +0800, guangrong.xiao@gmail.com wrote: >>>> From: Xiao Guangrong <xiaoguangrong@tencent.com> >>>> >>>> Currently the page being compressed is allowed to be updated by >>>> the VM on the source QEMU, correspondingly the destination QEMU >>>> just ignores the decompression error. However, we completely miss >>>> the chance to catch real errors, then the VM is corrupted silently >>>> >>>> To make the migration more robuster, we copy the page to a buffer >>>> first to avoid it being written by VM, then detect and handle the >>>> errors of both compression and decompression errors properly >>> >>> Not sure I missed anything important, but I'll just shoot my thoughts >>> as questions (again)... >>> >>> Actually this is a more general question? Say, even without >>> compression, we can be sending a page that is being modified. >>> >>> However, IMHO we don't need to worry that, since if that page is >>> modified, we'll definitely send that page again, so the new page will >>> replace the old. So on destination side, even if decompress() failed >>> on a page it'll be fine IMHO. Though now we are copying the corrupted >>> buffer. On that point, I fully agree that we should not - maybe we >>> can just drop the page entirely? >>> >>> For non-compress pages, we can't detect that, so we'll copy the page >>> even if corrupted. >>> >>> The special part for compression would be: would the deflate() fail if >>> there is concurrent update to the buffer being compressed? And would >>> that corrupt the whole compression stream, or it would only fail the >>> deflate() call? >> >> It is not the same for normal page and compressed page. >> >> For the normal page, the dirty-log mechanism in QEMU and the infrastructure >> of the network (e.g, TCP) can make sure that the modified memory will >> be posted to the destination without corruption. >> >> However, nothing can guarantee compression/decompression is BUG-free, >> e,g, consider the case, in the last step, vCPUs & dirty-log are paused and >> the memory is compressed and posted to destination, if there is any error >> in compression/decompression, VM dies silently. > > Here do you mean the compression error even if the VM is halted? I'd > say in that case IMHO the extra memcpy() would still help little since > the coiped page should exactly be the same as the source page? ”compression error“ means that compress2() in original code returns a error code. If the data being compressed is being modified at the some time, compression will fail and this failure is negative. We move the data to a internal buffer to avoid this case, so that we can catch the real error condition. > > I'd say I don't know what we can really do if there are zlib bugs. I > was assuming we'll definitely fail in a strange way if there is any, > which should be hard to be detected from QEMU's POV (maybe a > destination VM crash, as you mentioned). It'll be easy for us to > detect errors when we got error code returned from compress(), however > IMHO when we say "zlib bug" it can also mean that data is corrputed > even compress() and decompress() both returned with good state. > Ah, sorry, i abused the word "BUG". It does not mean the BUG in compression/decompression API, i mean the failure conditions (The API returns a error code). > It'll be understandable to me if the problem is that the compress() > API does not allow the input buffer to be changed during the whole > period of the call. If that is a must, this patch for sure helps. Yes, that is exactly what i want to say. :)
On 03/27/2018 07:17 PM, Peter Xu wrote: > On Tue, Mar 27, 2018 at 03:42:32AM +0800, Xiao Guangrong wrote: > > [...] > >>> It'll be understandable to me if the problem is that the compress() >>> API does not allow the input buffer to be changed during the whole >>> period of the call. If that is a must, this patch for sure helps. >> >> Yes, that is exactly what i want to say. :) > > So I think now I know what this patch is for. :) And yeah, it makes > sense. > > Though another question would be: if the buffer is updated during > compress() and compress() returned error, would that pollute the whole > z_stream or it only fails the compress() call? > I guess deflateReset() can recover everything, i.e, keep z_stream as it is init'ed by deflate_init(). > (Same question applies to decompress().) > > If it's only a compress() error and it won't pollute z_stream (or say, > it can be recovered after a deflateReset() and then we can continue to > call deflate() without problem), then we'll actually have two > alternatives to solve this "buffer update" issue: > > 1. Use the approach of current patch: we copy the page every time, so > deflate() never fails because update never happens. But it's slow > since we copy the pages every time. > > 2. Use the old approach, and when compress() fail, we just ignore that > page (since now we know that error _must_ be caused by page update, > then we are 100% sure that we'll send that page again so it'll be > perfectly fine). > No, we can't make the assumption that "error _must_ be caused by page update". No document/ABI about compress/decompress promised it. :) Thanks!
On Thu, Mar 22, 2018 at 08:03:53PM +0800, Xiao Guangrong wrote: > > > On 03/21/2018 06:00 PM, Peter Xu wrote: > > On Tue, Mar 13, 2018 at 03:57:34PM +0800, guangrong.xiao@gmail.com wrote: > > > From: Xiao Guangrong <xiaoguangrong@tencent.com> > > > > > > Currently the page being compressed is allowed to be updated by > > > the VM on the source QEMU, correspondingly the destination QEMU > > > just ignores the decompression error. However, we completely miss > > > the chance to catch real errors, then the VM is corrupted silently > > > > > > To make the migration more robuster, we copy the page to a buffer > > > first to avoid it being written by VM, then detect and handle the > > > errors of both compression and decompression errors properly > > > > Not sure I missed anything important, but I'll just shoot my thoughts > > as questions (again)... > > > > Actually this is a more general question? Say, even without > > compression, we can be sending a page that is being modified. > > > > However, IMHO we don't need to worry that, since if that page is > > modified, we'll definitely send that page again, so the new page will > > replace the old. So on destination side, even if decompress() failed > > on a page it'll be fine IMHO. Though now we are copying the corrupted > > buffer. On that point, I fully agree that we should not - maybe we > > can just drop the page entirely? > > > > For non-compress pages, we can't detect that, so we'll copy the page > > even if corrupted. > > > > The special part for compression would be: would the deflate() fail if > > there is concurrent update to the buffer being compressed? And would > > that corrupt the whole compression stream, or it would only fail the > > deflate() call? > > It is not the same for normal page and compressed page. > > For the normal page, the dirty-log mechanism in QEMU and the infrastructure > of the network (e.g, TCP) can make sure that the modified memory will > be posted to the destination without corruption. > > However, nothing can guarantee compression/decompression is BUG-free, > e,g, consider the case, in the last step, vCPUs & dirty-log are paused and > the memory is compressed and posted to destination, if there is any error > in compression/decompression, VM dies silently. Here do you mean the compression error even if the VM is halted? I'd say in that case IMHO the extra memcpy() would still help little since the coiped page should exactly be the same as the source page? I'd say I don't know what we can really do if there are zlib bugs. I was assuming we'll definitely fail in a strange way if there is any, which should be hard to be detected from QEMU's POV (maybe a destination VM crash, as you mentioned). It'll be easy for us to detect errors when we got error code returned from compress(), however IMHO when we say "zlib bug" it can also mean that data is corrputed even compress() and decompress() both returned with good state. It'll be understandable to me if the problem is that the compress() API does not allow the input buffer to be changed during the whole period of the call. If that is a must, this patch for sure helps. Thanks,
On Tue, Mar 27, 2018 at 03:42:32AM +0800, Xiao Guangrong wrote: [...] > > It'll be understandable to me if the problem is that the compress() > > API does not allow the input buffer to be changed during the whole > > period of the call. If that is a must, this patch for sure helps. > > Yes, that is exactly what i want to say. :) So I think now I know what this patch is for. :) And yeah, it makes sense. Though another question would be: if the buffer is updated during compress() and compress() returned error, would that pollute the whole z_stream or it only fails the compress() call? (Same question applies to decompress().) If it's only a compress() error and it won't pollute z_stream (or say, it can be recovered after a deflateReset() and then we can continue to call deflate() without problem), then we'll actually have two alternatives to solve this "buffer update" issue: 1. Use the approach of current patch: we copy the page every time, so deflate() never fails because update never happens. But it's slow since we copy the pages every time. 2. Use the old approach, and when compress() fail, we just ignore that page (since now we know that error _must_ be caused by page update, then we are 100% sure that we'll send that page again so it'll be perfectly fine). If you see, IMHO method 2 has its advantage, since actually it "detects" the page update operation by getting a failure in compress(), then we don't really need to send that page at all (since we'll send it later again, for sure). Then, we not only saved the memcpy() CPU time for every single page, meanwhile we might save some bandwidth since we won't bother to send the page when we know the page is modified. But all these depend on the assumption that: 1. compress() will fail only because of buffer update, and 2. compress() failures won't pollute the whole z_stream. Same thing would apply to decompress() side - we drop the corrupted page (when decompress() returned errors) since we know another one will come soon. It's a bit tricky, but I'm still curious about it, since actually that's mostly the old code before this patch except that we don't really drop corrputed pages but we still use them (which won't hurt too IMHO). Thanks,
On 03/28/2018 08:43 AM, jiang.biao2@zte.com.cn wrote: >> On 03/27/2018 07:17 PM, Peter Xu wrote: >>> On Tue, Mar 27, 2018 at 03:42:32AM +0800, Xiao Guangrong wrote: >>> >>> [...] >>> >>>>> It'll be understandable to me if the problem is that the compress() >>>>> API does not allow the input buffer to be changed during the whole >>>>> period of the call. If that is a must, this patch for sure helps. >>>> >>>> Yes, that is exactly what i want to say. :) >>> >>> So I think now I know what this patch is for. :) And yeah, it makes >>> sense. >>> >>> Though another question would be: if the buffer is updated during >>> compress() and compress() returned error, would that pollute the whole >>> z_stream or it only fails the compress() call? >>> >> >> I guess deflateReset() can recover everything, i.e, keep z_stream as >> it is init'ed by deflate_init(). >> >>> (Same question applies to decompress().) >>> >>> If it's only a compress() error and it won't pollute z_stream (or say, >>> it can be recovered after a deflateReset() and then we can continue to >>> call deflate() without problem), then we'll actually have two >>> alternatives to solve this "buffer update" issue: >>> >>> 1. Use the approach of current patch: we copy the page every time, so >>> deflate() never fails because update never happens. But it's slow >>> since we copy the pages every time. >>> >>> 2. Use the old approach, and when compress() fail, we just ignore that >>> page (since now we know that error _must_ be caused by page update, >>> then we are 100% sure that we'll send that page again so it'll be >>> perfectly fine). >>> >> >> No, we can't make the assumption that "error _must_ be caused by page update". >> No document/ABI about compress/decompress promised it. :) > So, as I metioned before, can we just distingush the decompress/compress errors > from errors caused by page update by the return code of inflate/deflate? > According to the zlib manual, there seems to be several error codes for different > cases, > #define Z_ERRNO (-1) > #define Z_STREAM_ERROR (-2) > #define Z_DATA_ERROR (-3) > #define Z_MEM_ERROR (-4) > #define Z_BUF_ERROR (-5) > #define Z_VERSION_ERROR (-6) > Did you check the return code when silent failure(not caused by page update) > happened before? :) I am afraid there is no such error code and i guess zlib is not designed to compress the data which is being modified.
On 03/28/2018 12:20 PM, Peter Xu wrote: > On Wed, Mar 28, 2018 at 12:08:19PM +0800, jiang.biao2@zte.com.cn wrote: >>> >>> On Tue, Mar 27, 2018 at 10:35:29PM +0800, Xiao Guangrong wrote: >>> >>>>>> No, we can't make the assumption that "error _must_ be caused by page update". >>>>>> No document/ABI about compress/decompress promised it. :) >>> >>> Indeed, I found no good documents about below errors that jiang.biao >>> pointed out. >> Hi, Peter >> The description about the errors comes from here, >> http://www.zlib.net/manual.html >> And about the error codes returned by inflate(), they are described as， >> ** inflate() returns >> Z_OK if some progress has been made (more input processed or more output produced), >> Z_STREAM_END if the end of the compressed data has been reached and all uncompressed output has been produced, >> Z_NEED_DICT if a preset dictionary is needed at this point, >> Z_DATA_ERROR if the input data was corrupted (input stream not conforming to the zlib format or incorrect check value, in which case strm->msg points to a string with a more specific error), >> Z_STREAM_ERROR if the stream structure was inconsistent (for example next_in or next_out was Z_NULL, or the state was inadvertently written over by the application), >> Z_MEM_ERROR if there was not enough memory, >> Z_BUF_ERROR if no progress was possible or if there was not enough room in the output buffer when Z_FINISH is used. ... >> ** > > Ah yes. My bad to be so uncareful. :) > >> According to the above description, the error caused by page update looks >> more like tend to return Z_DATA_ERROR, but I do not have env to verify that. :) No, still lack info to confirm the case of compressing the data being updated is the only one to return Z_DATA_ERROR. And nothing provided that no other error condition causes data corrupted will be squeezed into this error code. >> As I understand it, the real compress/decompress error cases other than that >> caused by page update should be rare, maybe the error code is enough to >> distinguish those if we can verify the the error codes returned by page update >> and other silent failures by test. If so, we can cut the cost of memcpy. Please note, compare with other operations, e.g, compression, detect zero page, etc., memcpy() is not a hot function at all. >> If not, I agree with Guangrong's idea too. I never read the zlib code and all my >> information comes from the manual, so if anything inaccurate, pls ignore my >> option. :) > > So I suppose all of us know that alternative now, we just need a solid > way to confirm the uncertainty. I'll leave this to Guangrong. Yes, i still prefer to memcpy() to make it safe enough to protect our production unless we get enough certainty to figure out the error conditions. Thanks!
> On 03/27/2018 07:17 PM, Peter Xu wrote: >> On Tue, Mar 27, 2018 at 03:42:32AM +0800, Xiao Guangrong wrote: >> >> [...] >> >>>> It'll be understandable to me if the problem is that the compress() >>>> API does not allow the input buffer to be changed during the whole >>>> period of the call. If that is a must, this patch for sure helps. >>> >>> Yes, that is exactly what i want to say. :) >> >> So I think now I know what this patch is for. :) And yeah, it makes >> sense. >> >> Though another question would be: if the buffer is updated during >> compress() and compress() returned error, would that pollute the whole >> z_stream or it only fails the compress() call? >> > > I guess deflateReset() can recover everything, i.e, keep z_stream as > it is init'ed by deflate_init(). > >> (Same question applies to decompress().) >> >> If it's only a compress() error and it won't pollute z_stream (or say, >> it can be recovered after a deflateReset() and then we can continue to >> call deflate() without problem), then we'll actually have two >> alternatives to solve this "buffer update" issue: >> >> 1. Use the approach of current patch: we copy the page every time, so >> deflate() never fails because update never happens. But it's slow >> since we copy the pages every time. >> >> 2. Use the old approach, and when compress() fail, we just ignore that >> page (since now we know that error _must_ be caused by page update, >> then we are 100% sure that we'll send that page again so it'll be >> perfectly fine). >> > > No, we can't make the assumption that "error _must_ be caused by page update". > No document/ABI about compress/decompress promised it. :) So, as I metioned before, can we just distingush the decompress/compress errors from errors caused by page update by the return code of inflate/deflate? According to the zlib manual, there seems to be several error codes for different cases, #define Z_ERRNO (-1) #define Z_STREAM_ERROR (-2) #define Z_DATA_ERROR (-3) #define Z_MEM_ERROR (-4) #define Z_BUF_ERROR (-5) #define Z_VERSION_ERROR (-6) Did you check the return code when silent failure(not caused by page update) happened before? :) Jiang Regards
On Tue, Mar 27, 2018 at 10:35:29PM +0800, Xiao Guangrong wrote: > > > On 03/28/2018 08:43 AM, jiang.biao2@zte.com.cn wrote: > > > On 03/27/2018 07:17 PM, Peter Xu wrote: > > > > On Tue, Mar 27, 2018 at 03:42:32AM +0800, Xiao Guangrong wrote: > > > > > > > > [...] > > > > > > > > > > It'll be understandable to me if the problem is that the compress() > > > > > > API does not allow the input buffer to be changed during the whole > > > > > > period of the call. If that is a must, this patch for sure helps. > > > > > > > > > > Yes, that is exactly what i want to say. :) > > > > > > > > So I think now I know what this patch is for. :) And yeah, it makes > > > > sense. > > > > > > > > Though another question would be: if the buffer is updated during > > > > compress() and compress() returned error, would that pollute the whole > > > > z_stream or it only fails the compress() call? > > > > > > > > > > I guess deflateReset() can recover everything, i.e, keep z_stream as > > > it is init'ed by deflate_init(). > > > > > > > (Same question applies to decompress().) > > > > > > > > If it's only a compress() error and it won't pollute z_stream (or say, > > > > it can be recovered after a deflateReset() and then we can continue to > > > > call deflate() without problem), then we'll actually have two > > > > alternatives to solve this "buffer update" issue: > > > > > > > > 1. Use the approach of current patch: we copy the page every time, so > > > > deflate() never fails because update never happens. But it's slow > > > > since we copy the pages every time. > > > > > > > > 2. Use the old approach, and when compress() fail, we just ignore that > > > > page (since now we know that error _must_ be caused by page update, > > > > then we are 100% sure that we'll send that page again so it'll be > > > > perfectly fine). > > > > > > > > > > No, we can't make the assumption that "error _must_ be caused by page update". > > > No document/ABI about compress/decompress promised it. :) Indeed, I found no good documents about below errors that jiang.biao pointed out. > > So, as I metioned before, can we just distingush the decompress/compress errors > > from errors caused by page update by the return code of inflate/deflate? > > According to the zlib manual, there seems to be several error codes for different > > cases, > > #define Z_ERRNO (-1) > > #define Z_STREAM_ERROR (-2) > > #define Z_DATA_ERROR (-3) > > #define Z_MEM_ERROR (-4) > > #define Z_BUF_ERROR (-5) > > #define Z_VERSION_ERROR (-6) > > Did you check the return code when silent failure(not caused by page update) > > happened before? :) > > I am afraid there is no such error code and i guess zlib is not designed to > compress the data which is being modified. So I agree with you, maybe the only right way to do now is copy the page, until we know better about zlib and find something useful. Thanks!
> > On Tue, Mar 27, 2018 at 10:35:29PM +0800, Xiao Guangrong wrote: > >> > > No, we can't make the assumption that "error _must_ be caused by page update". >> > > No document/ABI about compress/decompress promised it. :) > > Indeed, I found no good documents about below errors that jiang.biao > pointed out. Hi, Peter The description about the errors comes from here, http://www.zlib.net/manual.html And about the error codes returned by inflate(), they are described as， ** inflate() returns Z_OK if some progress has been made (more input processed or more output produced), Z_STREAM_END if the end of the compressed data has been reached and all uncompressed output has been produced, Z_NEED_DICT if a preset dictionary is needed at this point, Z_DATA_ERROR if the input data was corrupted (input stream not conforming to the zlib format or incorrect check value, in which case strm->msg points to a string with a more specific error), Z_STREAM_ERROR if the stream structure was inconsistent (for example next_in or next_out was Z_NULL, or the state was inadvertently written over by the application), Z_MEM_ERROR if there was not enough memory, Z_BUF_ERROR if no progress was possible or if there was not enough room in the output buffer when Z_FINISH is used. ... ** According to the above description, the error caused by page update looks more like tend to return Z_DATA_ERROR, but I do not have env to verify that. :) As I understand it, the real compress/decompress error cases other than that caused by page update should be rare, maybe the error code is enough to distinguish those if we can verify the the error codes returned by page update and other silent failures by test. If so, we can cut the cost of memcpy. If not, I agree with Guangrong's idea too. I never read the zlib code and all my information comes from the manual, so if anything inaccurate, pls ignore my option. :) Regards, Jiang
On Wed, Mar 28, 2018 at 12:08:19PM +0800, jiang.biao2@zte.com.cn wrote: > > > > On Tue, Mar 27, 2018 at 10:35:29PM +0800, Xiao Guangrong wrote: > > > >> > > No, we can't make the assumption that "error _must_ be caused by page update". > >> > > No document/ABI about compress/decompress promised it. :) > > > > Indeed, I found no good documents about below errors that jiang.biao > > pointed out. > Hi, Peter > The description about the errors comes from here, > http://www.zlib.net/manual.html > And about the error codes returned by inflate(), they are described as， > ** inflate() returns > Z_OK if some progress has been made (more input processed or more output produced), > Z_STREAM_END if the end of the compressed data has been reached and all uncompressed output has been produced, > Z_NEED_DICT if a preset dictionary is needed at this point, > Z_DATA_ERROR if the input data was corrupted (input stream not conforming to the zlib format or incorrect check value, in which case strm->msg points to a string with a more specific error), > Z_STREAM_ERROR if the stream structure was inconsistent (for example next_in or next_out was Z_NULL, or the state was inadvertently written over by the application), > Z_MEM_ERROR if there was not enough memory, > Z_BUF_ERROR if no progress was possible or if there was not enough room in the output buffer when Z_FINISH is used. ... > ** Ah yes. My bad to be so uncareful. :) > According to the above description, the error caused by page update looks > more like tend to return Z_DATA_ERROR, but I do not have env to verify that. :) > As I understand it, the real compress/decompress error cases other than that > caused by page update should be rare, maybe the error code is enough to > distinguish those if we can verify the the error codes returned by page update > and other silent failures by test. If so, we can cut the cost of memcpy. > If not, I agree with Guangrong's idea too. I never read the zlib code and all my > information comes from the manual, so if anything inaccurate, pls ignore my > option. :) So I suppose all of us know that alternative now, we just need a solid way to confirm the uncertainty. I'll leave this to Guangrong. Thanks,
> On 03/28/2018 12:20 PM, Peter Xu wrote: >> On Wed, Mar 28, 2018 at 12:08:19PM +0800, jiang.biao2@zte.com.cn wrote: >>>> >>>> On Tue, Mar 27, 2018 at 10:35:29PM +0800, Xiao Guangrong wrote: >>>> >>>>>>> No, we can't make the assumption that "error _must_ be caused by page update". >>>>>>> No document/ABI about compress/decompress promised it. :) >>>> >>>> Indeed, I found no good documents about below errors that jiang.biao >>>> pointed out. >>> Hi, Peter >>> The description about the errors comes from here, >>> http://www.zlib.net/manual.html >>> And about the error codes returned by inflate(), they are described as， >>> ** inflate() returns >>> Z_OK if some progress has been made (more input processed or more output produced), >>> Z_STREAM_END if the end of the compressed data has been reached and all uncompressed output has been produced, >>> Z_NEED_DICT if a preset dictionary is needed at this point, >>> Z_DATA_ERROR if the input data was corrupted (input stream not conforming to the zlib format or incorrect check value, in which case strm->msg points to a string with a >more specific error), >>> Z_STREAM_ERROR if the stream structure was inconsistent (for example next_in or next_out was Z_NULL, or the state was inadvertently written over by the application), >>> Z_MEM_ERROR if there was not enough memory, >>> Z_BUF_ERROR if no progress was possible or if there was not enough room in the output buffer when Z_FINISH is used. ... >>> ** >> >> Ah yes. My bad to be so uncareful. :) >> >>> According to the above description, the error caused by page update looks >>> more like tend to return Z_DATA_ERROR, but I do not have env to verify that. :) > > No, still lack info to confirm the case of compressing the data being > updated is the only one to return Z_DATA_ERROR. And nothing provided > that no other error condition causes data corrupted will be squeezed > into this error code. > >>> As I understand it, the real compress/decompress error cases other than that >>> caused by page update should be rare, maybe the error code is enough to >>> distinguish those if we can verify the the error codes returned by page update >>> and other silent failures by test. If so, we can cut the cost of memcpy. > > Please note, compare with other operations, e.g, compression, detect zero page, > etc., memcpy() is not a hot function at all. Just out of curiousity, what's level of memory num need to be copied for normal cases? KBs, MBs? >>> If not, I agree with Guangrong's idea too. I never read the zlib code and all my >>> information comes from the manual, so if anything inaccurate, pls ignore my >>> option. :) >> >> So I suppose all of us know that alternative now, we just need a solid >> way to confirm the uncertainty. I'll leave this to Guangrong. > > Yes, i still prefer to memcpy() to make it safe enough to protect our production > unless we get enough certainty to figure out the error conditions. Indeed, no garantee for that currently, so for safe, we need memcpy(). Never mind, pls just ignore my opinion. :) Thanks! Regards, Jiang
diff --git a/migration/qemu-file.c b/migration/qemu-file.c index 1ff33a1ffb..137bcc8bdc 100644 --- a/migration/qemu-file.c +++ b/migration/qemu-file.c @@ -711,9 +711,9 @@ ssize_t qemu_put_compression_data(QEMUFile *f, z_stream *stream, blen = qemu_compress_data(stream, f->buf + f->buf_index + sizeof(int32_t), blen, p, size); if (blen < 0) { - error_report("Compress Failed!"); - return 0; + return -1; } + qemu_put_be32(f, blen); if (f->ops->writev_buffer) { add_to_iovec(f, f->buf + f->buf_index, blen, false); diff --git a/migration/ram.c b/migration/ram.c index fff3f31e90..c47185d38c 100644 --- a/migration/ram.c +++ b/migration/ram.c @@ -273,6 +273,7 @@ struct DecompressParam { bool quit; QemuMutex mutex; QemuCond cond; + QEMUFile *file; void *des; uint8_t *compbuf; int len; @@ -1051,11 +1052,13 @@ static int do_compress_ram_page(QEMUFile *f, z_stream *stream, RAMBlock *block, { RAMState *rs = ram_state; int bytes_sent, blen; - uint8_t *p = block->host + (offset & TARGET_PAGE_MASK); + uint8_t buf[TARGET_PAGE_SIZE], *p; + p = block->host + (offset & TARGET_PAGE_MASK); bytes_sent = save_page_header(rs, f, block, offset | RAM_SAVE_FLAG_COMPRESS_PAGE); - blen = qemu_put_compression_data(f, stream, p, TARGET_PAGE_SIZE); + memcpy(buf, p, TARGET_PAGE_SIZE); + blen = qemu_put_compression_data(f, stream, buf, TARGET_PAGE_SIZE); if (blen < 0) { bytes_sent = 0; qemu_file_set_error(migrate_get_current()->to_dst_file, blen); @@ -2547,7 +2550,7 @@ static void *do_data_decompress(void *opaque) DecompressParam *param = opaque; unsigned long pagesize; uint8_t *des; - int len; + int len, ret; qemu_mutex_lock(¶m->mutex); while (!param->quit) { @@ -2563,8 +2566,12 @@ static void *do_data_decompress(void *opaque) * not a problem because the dirty page will be retransferred * and uncompress() won't break the data in other pages. */ - qemu_uncompress(¶m->stream, des, pagesize, - param->compbuf, len); + ret = qemu_uncompress(¶m->stream, des, pagesize, + param->compbuf, len); + if (ret < 0) { + error_report("decompress data failed"); + qemu_file_set_error(param->file, ret); + } qemu_mutex_lock(&decomp_done_lock); param->done = true; @@ -2581,12 +2588,12 @@ static void *do_data_decompress(void *opaque) return NULL; } -static void wait_for_decompress_done(void) +static int wait_for_decompress_done(QEMUFile *f) { int idx, thread_count; if (!migrate_use_compression()) { - return; + return 0; } thread_count = migrate_decompress_threads(); @@ -2597,6 +2604,7 @@ static void wait_for_decompress_done(void) } } qemu_mutex_unlock(&decomp_done_lock); + return qemu_file_get_error(f); } static void compress_threads_load_cleanup(void) @@ -2635,7 +2643,7 @@ static void compress_threads_load_cleanup(void) decomp_param = NULL; } -static int compress_threads_load_setup(void) +static int compress_threads_load_setup(QEMUFile *f) { int i, thread_count; @@ -2654,6 +2662,7 @@ static int compress_threads_load_setup(void) } decomp_param[i].stream.opaque = &decomp_param[i]; + decomp_param[i].file = f; qemu_mutex_init(&decomp_param[i].mutex); qemu_cond_init(&decomp_param[i].cond); decomp_param[i].compbuf = g_malloc0(compressBound(TARGET_PAGE_SIZE)); @@ -2708,7 +2717,7 @@ static void decompress_data_with_multi_threads(QEMUFile *f, */ static int ram_load_setup(QEMUFile *f, void *opaque) { - if (compress_threads_load_setup()) { + if (compress_threads_load_setup(f)) { return -1; } @@ -3063,7 +3072,7 @@ static int ram_load(QEMUFile *f, void *opaque, int version_id) } } - wait_for_decompress_done(); + ret |= wait_for_decompress_done(f); rcu_read_unlock(); trace_ram_load_complete(ret, seq_iter); return ret;