Hello Cliff, On Tue, 23 Oct 2012 17:51:05 -0500 Cliff Wickman <cpw at sgi.com> wrote: > Hello Mr. Kumagai, > > I was looking for some information about the "cyclic" processing in > makedumpfile, and came upon this: > http://lists.infradead.org/pipermail/kexec/2012-July/006480.html > That's why I'm sending this question to you. Thank you for your suggestion for improvement. > I work on the Linux kernel here at SGI. We are trying to dump some very > large memories, and so we are very interested in this cyclic feature. > > I built makedumpfile-1.5.0 and tried it out. > It seems to work fine, but does spend a lot of time building bitmaps. > > If I set the cyclic-buffer value to create 3 cycles, then > exclude_unneccessary_pages_cyclic() is entered 6 times: > - 3 times from get_num_dumpable_cyclic() (via update_region_cyclic()) > - 3 times from write_kdump_pages_and_bitmap_cyclic() > (also via update_region_cyclic()) > > These page structure scans of /proc/vmcore for terabytes of memory can > take a long time, and so I think something might be done to remove the > redundant scans. > > Could it not be possible to save the bitmaps created during the > get_num_dumpable_cyclic() pass? And then retrieve them for the > write_kdump_pages_and_bitmap_cyclic() pass? I think this could save > literally hours on a very large memory. > > Perhaps they could be written to a file, or files. makedumpfile should work also on the environment which doesn't mount a root filesystem when 2nd-kernel is running. In such environments, writing to a file isn't the solution because the bitmap file is created on 2nd-kernel's memory. This is the starting point of our discussion. Therefore, we can save only a chunk of bitmap at a time, so we have to scan each region twice. > But I'm sure you understand the logic of makedumpfile much better than I. > Do you think such an enhancement is possible? > Or perhaps you already have another workaround? Now, I plan to do the two enhancement for performance, please see below. in v1.5.1: - Minimaize the number of cycle http://lists.infradead.org/pipermail/kexec/2012-October/006864.html in v1.5.2: - Improve the filtering logic http://lists.infradead.org/pipermail/kexec/2012-June/006441.html Thanks Atsushi Kumagai > > Thanks much. > -Cliff Wickman
