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| H A D | image.c | diff 272384 Wed Oct 01 19:03:18 MDT 2014 marcel Improve performance of mking(1) by keeping a list of "chunks" in memory, that keeps track of a particular region of the image. In particular the image_data() function needs to return to the caller whether a region contains data or is all zeroes. This required reading the region from the temporary file and comparing the bytes. When image_data() is used multiple times for the same region, this will get painful fast. With a chunk describing a region of the image, we now also have a way to refer to the image provided on the command line. This means we don't need to copy the image into a temporary file. We just keep track of the file descriptor and offset within the source file on a per-chunk basis. For streams (pipes, sockets, fifos, etc) we now use the temporary file as a swap file. We read from the input file and create a chunk of type "zeroes" for each sequence of zeroes that's a multiple of the sector size. Otherwise, we allocte from the swap file, mmap(2) it, read into the mmap(2)'d memory and create a chunk representing data. For regular files, we use SEEK_HOLE and SEEK_DATA to handle sparse files eficiently and create a chunk of type zeroes for holes and a chunk of type data for data regions. For data regions, we still compare the bytes we read to handle differences between a file system's block size and our sector size. After reading all files, image_write() is used by schemes to scribble in the reserved sectors. Since this never amounts to much, keep this data in memory in chunks of exactly 1 sector. The output image is created by looking using the chunk list to find the data and write it out to the output file. For chunks of type "zeroes" we prefer to seek, but fall back to writing zeroes to handle pipes. For chunks of type "file" and "memoty" we simply write. The net effect of this is that for reasonably large images the execution time drops from 1-2 minutes to 10-20 seconds. A typical speedup is about 5 to 8 times, depending on partition sizes, output format whether in input files are sparse or not. Bump version to 20141001. |
| H A D | Makefile | diff 272384 Wed Oct 01 19:03:18 MDT 2014 marcel Improve performance of mking(1) by keeping a list of "chunks" in memory, that keeps track of a particular region of the image. In particular the image_data() function needs to return to the caller whether a region contains data or is all zeroes. This required reading the region from the temporary file and comparing the bytes. When image_data() is used multiple times for the same region, this will get painful fast. With a chunk describing a region of the image, we now also have a way to refer to the image provided on the command line. This means we don't need to copy the image into a temporary file. We just keep track of the file descriptor and offset within the source file on a per-chunk basis. For streams (pipes, sockets, fifos, etc) we now use the temporary file as a swap file. We read from the input file and create a chunk of type "zeroes" for each sequence of zeroes that's a multiple of the sector size. Otherwise, we allocte from the swap file, mmap(2) it, read into the mmap(2)'d memory and create a chunk representing data. For regular files, we use SEEK_HOLE and SEEK_DATA to handle sparse files eficiently and create a chunk of type zeroes for holes and a chunk of type data for data regions. For data regions, we still compare the bytes we read to handle differences between a file system's block size and our sector size. After reading all files, image_write() is used by schemes to scribble in the reserved sectors. Since this never amounts to much, keep this data in memory in chunks of exactly 1 sector. The output image is created by looking using the chunk list to find the data and write it out to the output file. For chunks of type "zeroes" we prefer to seek, but fall back to writing zeroes to handle pipes. For chunks of type "file" and "memoty" we simply write. The net effect of this is that for reasonably large images the execution time drops from 1-2 minutes to 10-20 seconds. A typical speedup is about 5 to 8 times, depending on partition sizes, output format whether in input files are sparse or not. Bump version to 20141001. |
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