On Sat, 2011-06-25 at 21:50 +0100, Shriram Rajagopalan wrote:
> # HG changeset patch
> # User Shriram Rajagopalan <rshriram@xxxxxxxxx>
> # Date 1309034380 25200
> # Node ID 1547d25fe51b0c84b908ca4fce02568f77b431b0
> # Parent c31e9249893d309655a8e739ba2ecb07d2c0148b
> tools/libxc: Document checkpoint compression in xg_save_restore.h
>
> Add comments to xg_save_restore.h explaining changes in Remus
> wire protocol when checkpoint compression is enabled.
>
> Signed-off-by: Shriram Rajagopalan <rshriram@xxxxxxxxx>
Thanks Shriram.
Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
>
> diff -r c31e9249893d -r 1547d25fe51b tools/libxc/xg_save_restore.h
> --- a/tools/libxc/xg_save_restore.h Sat Jun 18 20:52:07 2011 -0700
> +++ b/tools/libxc/xg_save_restore.h Sat Jun 25 13:39:40 2011 -0700
> @@ -67,7 +67,7 @@
> *
> * consists of p2m_size bytes comprising an array of xen_pfn_t sized
> entries.
> *
> - * BODY PHASE
> + * BODY PHASE - Format A (for live migration or Remus without compression)
> * ----------
> *
> * A series of chunks with a common header:
> @@ -87,6 +87,113 @@
> *
> * If chunk type is 0 then body phase is complete.
> *
> + *
> + * BODY PHASE - Format B (for Remus with compression)
> + * ----------
> + *
> + * A series of chunks with a common header:
> + * int : chunk type
> + *
> + * If the chunk type is +ve then chunk contains array of PFNs corresponding
> + * to guest memory and type contains the number of PFNs in the batch:
> + *
> + * unsigned long[] : PFN array, length == number of pages in batch
> + * Each entry consists of XEN_DOMCTL_PFINFO_*
> + * in bits 31-28 and the PFN number in bits 27-0.
> + *
> + * If the chunk type is -ve then chunk consists of one of a number of
> + * metadata types. See definitions of XC_SAVE_ID_* below.
> + *
> + * If the chunk type is -ve and equals XC_SAVE_ID_COMPRESSED_DATA, then the
> + * chunk consists of compressed page data, in the following format:
> + *
> + * unsigned long : Size of the compressed chunk to follow
> + * compressed data : variable length data of size indicated above.
> + * This chunk consists of compressed page data.
> + * The number of pages in one chunk depends on
> + * the amount of space available in the sender's
> + * output buffer.
> + *
> + * Format of compressed data:
> + * compressed_data = (BEGIN_PAGE,<deltas>*) | (FULL_PAGE,4096 bytes)
> + * delta = <+ve offset in page (2byte), value (4byte)>
> + * BEGIN_PAGE = a dummy delta with offset = -100 and value = 0
> + * FULL_PAGE = a dummy delta with offset = -101 and value = 0
> + *
> + * If chunk type is 0 then body phase is complete.
> + *
> + * There can be one or more chunks with type XC_SAVE_ID_COMPRESSED_DATA,
> + * containing compressed pages. The compressed chunks are collated to form
> + * one single compressed chunk for the entire iteration. The number of pages
> + * present in this final compressed chunk will be equal to the total number
> + * of valid PFNs specified by the +ve chunks.
> + *
> + * At the sender side, compressed pages are inserted into the output stream
> + * in the same order as they would have been if compression logic was absent.
> + *
> + * Until last iteration, the BODY is sent in Format A, to maintain live
> + * migration compatibility with receivers of older Xen versions.
> + * At the last iteration, if Remus compression was enabled, the sender sends
> + * a trigger, XC_SAVE_ID_ENABLE_COMPRESSION to tell the receiver to parse the
> + * BODY in Format B from the next iteration onwards.
> + *
> + * An example sequence of chunks received in Format B:
> + * +16 +ve chunk
> + * unsigned long[16] PFN array
> + * +100 +ve chunk
> + * unsigned long[100] PFN array
> + * +50 +ve chunk
> + * unsigned long[50] PFN array
> + *
> + * XC_SAVE_ID_COMPRESSED_DATA TAG
> + * N Length of compressed data
> + * N bytes of DATA Decompresses to 166 pages
> + *
> + * XC_SAVE_ID_* other xc save chunks
> + * 0 END BODY TAG
> + *
> + * Corner case with checkpoint compression:
> + * At sender side, after pausing the domain, dirty pages are usually
> + * copied out to a temporary buffer. After the domain is resumed,
> + * compression is done and the compressed chunk(s) are sent, followed by
> + * other XC_SAVE_ID_* chunks.
> + * If the temporary buffer gets full while scanning for dirty pages,
> + * the sender stops buffering of dirty pages, compresses the temporary
> + * buffer and sends the compressed data with XC_SAVE_ID_COMPRESSED_DATA.
> + * The sender then resumes the buffering of dirty pages and continues
> + * scanning for the dirty pages.
> + * For e.g., assume that the temporary buffer can hold 4096 pages and
> + * there are 5000 dirty pages. The following is the sequence of chunks
> + * that the receiver will see:
> + *
> + * +1024 +ve chunk
> + * unsigned long[1024] PFN array
> + * +1024 +ve chunk
> + * unsigned long[1024] PFN array
> + * +1024 +ve chunk
> + * unsigned long[1024] PFN array
> + * +1024 +ve chunk
> + * unsigned long[1024] PFN array
> + *
> + * XC_SAVE_ID_COMPRESSED_DATA TAG
> + * N Length of compressed data
> + * N bytes of DATA Decompresses to 4096 pages
> + *
> + * +4 +ve chunk
> + * unsigned long[4] PFN array
> + *
> + * XC_SAVE_ID_COMPRESSED_DATA TAG
> + * M Length of compressed data
> + * M bytes of DATA Decompresses to 4 pages
> + *
> + * XC_SAVE_ID_* other xc save chunks
> + * 0 END BODY TAG
> + *
> + * In other words, XC_SAVE_ID_COMPRESSED_DATA can be interleaved with
> + * +ve chunks arbitrarily. But at the receiver end, the following condition
> + * always holds true until the end of BODY PHASE:
> + * num(PFN entries +ve chunks) >= num(pages received in compressed form)
> + *
> * TAIL PHASE
> * ----------
> *
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel
|
Home