I have run some tests with the latest makedumpfile and kexec and the results (below) look very good to me. This particular test machine has a megaraid root, which had been a problem with previous kexec-tools (I did have to allocate a lot of low memory). My 3.10 kernel does have Hatayama's vmcore mmap patches. My only remaining concern for makedumpfile is the filtering of huge pages. I believe that patch is in progress; but I don't see it in 1.5.4. -Cliff UV2000 memory: 734G makedumpfile: makedumpfile-1.5.4 kexec: git://git.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git booted with crashkernel=1G,high crashkernel=192M,low non-cyclic mode write to option init&scan sec. copy sec. dump size ------------- ----------------- ---- --------- --------- megaraid disk no compression 19 91 11.7G megaraid disk zlib compression 20 209 1.4G megaraid disk snappy compression 20 46 2.4G megaraid disk snappy compression no mmap 30 72 2.4G /dev/null no compression 19 28 - /dev/null zlib compression 19 206 - /dev/null snappy compression 19 41 - Notes and observations - Snappy compression is a big win over zlib compression; over 4 times faster with a cost of relatively little disk space. - The vmcore mmap kernel patch cuts off about 1/3 of both page scan time and data copy time. I hope those patches reach Linus' tree shortly, as you expect. - Data copy time is dominated by compression time; writing compressed data to /dev/null uses almost the same time as writing to disk. I hope your efforts to multi-thread the crash kernel go forward. -- Cliff Wickman SGI cpw at sgi.com (651) 683-3824
