-----Original Message----- > -----Original Message----- > > > > > This patch set adds ZSTD compression support to makedumpfile. With ZSTD compression > > > > > support, the vmcore dump size and time consumption can have a better balance than > > > > > zlib/lzo/snappy. > > > > > > > > > > How to build: > > > > > > > > > > Build using make: > > > > > $ make USEZSTD=on > > > > > > > > > > Performance Comparison: > > > > > > > > > > How to measure > > > > > > > > > > I took a x86_64 machine which had 4T memory, and the compression level > > > > > range from (-3 to 4) for ZSTD, as well as zlib/lzo/snappy compression. > > > > > All testing was done by makedumpfile single thread mode. > > > > > > > > > > As for compression performance testing, in order to avoid the performance > > > > > bottle neck of disk I/O, I used the following makedumpfile cmd, which took > > > > > lzo compression as an example. "--dry-run" will not write any data to disk, > > > > > "--show-stat" will output the vmcore size after compression, and the time > > > > > consumption can be collected from the output logs. > > > > > > > > > > $ makedumpfile -d 0 -l /proc/kcore vmcore --dry-run --show-stat > > > > > > > > > > > > > > > As for decompression performance testing, I only tested the (-d 31) case, > > > > > because the vmcore size of (-d 0) case is too big to fit in the disk, in > > > > > addtion, to read a oversized file from disk will encounter the disk I/O > > > > > bottle neck. > > > > > > > > > > I triggered a kernel crash and collected a vmcore. Then I converted the > > > > > vmcore into specific compression format using the following makedumpfile > > > > > cmd, which would get a lzo format vmcore as an example: > > > > > > > > > > $ makedumpfile -l vmcore vmcore.lzo > > > > > > > > > > After all vmcores were ready, I used the following cmd to perform the > > > > > decompression, the time consumption can be collected from the logs. > > > > > > > > > > $ makedumpfile -F vmcore.lzo --dry-run --show-stat > > > > > > > > > > > > > > > Result charts > > > > > > > > > > For compression: > > > > > > > > > > makedumpfile -d31 | makedumpfile -d0 > > > > > Compression time vmcore size | Compression time vmcore size > > > > > zstd-3 325.516446 5285179595 | 8205.452248 51715430204 > > > > > zstd-2 332.069432 5319726604 | 8057.381371 51732062793 > > > > > zstd-1 309.942773 5730516274 | 8138.060786 52136191571 > > > > > zstd0 439.773076 4673859661 | 8873.059963 50993669657 > > > > > zstd1 406.68036 4700959521 | 8259.417132 51036900055 > > > > > zstd2 397.195643 4699263608 | 8230.308291 51030410942 > > > > > zstd3 436.491632 4673306398 | 8803.970103 51043393637 > > > > > zstd4 543.363928 4668419304 | 8991.240244 51058088514 > > > > > zlib 561.217381 8514803195 | 14381.755611 78199283893 > > > > > lzo 248.175953 16696411879 | 6057.528781 90020895741 > > > > > snappy 231.868312 11782236674 | 5290.919894 245661288355 > > > > > > > > > > For decompression: > > > > > > > > > > makedumpfile -d31 > > > > > decompress time vmcore size > > > > > zstd-3 477.543396 5289373448 > > > > > zstd-2 478.034534 5327454123 > > > > > zstd-1 459.066807 5748037931 > > > > > zstd0 561.687525 4680009013 > > > > > zstd1 547.248917 4706358547 > > > > > zstd2 544.219758 4704780719 > > > > > zstd3 555.726343 4680009013 > > > > > zstd4 558.031721 4675545933 > > > > > zlib 630.965426 8555376229 > > > > > lzo 427.292107 16849457649 > > > > > snappy 446.542806 11841407957 > > > > > > > > > > Discussion > > > > > > > > > > For zstd range from -3 to 4, compression level 2 (ZSTD_dfast) has > > > > > the best time consumption and vmcore dump size balance. > > > > > > > > Do you have a result of -d 1 compression test? I think -d 0 is not > > > > practical, I would like to see a -d 1 result of such a large vmcore. > > > > > > > > > > No, I haven't tested the -d 1 case. I have returned the machine which used > > > for performance testing, I will borrow and test on it again, please wait for > > > a while... > > > > Thanks, it would be helpful. > > > > > > > > > And just out of curiosity, what version of zstd are you using? > > > > When I tested zstd last time, compression level 1 was faster than 2, iirc. > > > > > > > > > > The OS running on the machine is fedora34, I used its default zstd package, whose > > > version is v1.4.9. > > > > Thanks for the info. > > > > > > > > > btw, ZSTD_dfast is an enum of ZSTD_strategy, not for compression level? > > > > > > Yes, it's enum of ZSTD_strategy [1]. > > > > ok, so it'll have to be replaced with "2" to avoid confusion. > > > > > > > > [1]: https://zstd.docsforge.com/dev/api-documentation/#advanced-compression-api-requires-v140 > > > > > > Thanks, > > > Tao Liu > > > > > > > (no need to update for now, I will review later) > > > > The series almost looks good to me (though I will merge those into a patch), > > just two questions are: > > - whether 2 is the best balanced compression level, As far as I've tested on two machines this time, compression level 1 was faster than 2. There is no large difference between them, but generally 1 should be faster than 2 according to the zstd manual: "The lower the level, the faster the speed (at the cost of compression)." And as you know, level 0 is unstable, that was the same when I tested before. So currently I would prefer 1 rather than 2, what do you think? Results: * RHEL8.4 with libzstd-1.4.4 / 64GB filled with QEMU memory/images mainly # free total used free shared buff/cache available Mem: 65599824 21768028 549364 4668 43282432 43078828 Swap: 32964604 4827916 28136688 makedumpfile -d 1 makedumpfile -d 31 copy sec. write bytes copy sec. write bytes zstd1 220.979689 26456659213 9.014176 558845000 zstd2 227.774602 26402437190 9.078599 560681256 lzo 83.406291 33078995065 3.603778 810219860 * RHEL with libzstd-1.5.0 / 64GB filled with kernel source code mainly # free total used free shared buff/cache available Mem: 65329632 9925536 456020 53086068 54948076 1549088 Swap: 32866300 1607424 31258876 makedumpfile -d 1 makedumpfile -d 31 zstd1 520.844189 15537080819 53.494782 1200754023 zstd2 533.912451 15469575651 53.641510 1199561609 lzo 233.370800 20780821165 23.281374 1740041245 (Used /proc/kcore, so not stable memory, but measured zstd 3 times and picked the middle elapsed time.) Thanks, Kazu _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
