I have proposed a patch to makedumpfile to (optionally) exclude from a dump the page structures representing excluded pages. The idea being that a system with terabytes of system memory has millions of pages of page structures. And most of them are unneeded. That patch thread begins here: http://marc.info/?l=kexec&m=138853299130125&w=2 Dave [Anderson] raised these crash-related issues; Although I'm sure you tested this, I find it amazing that only the "kmem -[fF]" option is the only command option that is affected? If I'm not mistaken, this would be the first time that legitimate kernel data would be excluded from the dump, and the user would have no obvious way of knowing that it had been done, correct? If it were encoded in the in the header somewhere, at least a warning message could be printed during crash initialization. ... Right, but look at all of the other page struct offsets in addition to page.lru that are used. The page.flags usage comes to mind, and for example, what would "kmem -p" display for the missing pages? Or "kmem <address>"? And would "kmem -i" display invalid data? I'm just speculating off the top of my head, but the page structure is such a fundamental data structure with several of its fields being used, just enter "help -o page_" to see all of its potential member usages. So I am submitting two patches for your consideration, should the patch to exclude unused vmemmap pages be taken into makedumpfile. - [PATCH 1/2] crash: initial note of excluded page structures This one makes crash startup look like this: This program has absolutely no warranty. Enter "help warranty" for details. NOTE: Unused vmemmap page structures are excluded from this dump. GNU gdb (GDB) 7.6 Copyright (C) 2013 Free Software Foundation, Inc. - [PATCH 1/2] crash: kmem warnings for excluded page structures This patch modifies kmem options -f, -F, -s addr, -S addr, and -i. Those are the only options that I could detect looking for excluded pages. This patch applies on top of the first, and adds some warnings to the output of these kmem options. For example: crash> kmem -f Note: kmem -f may fail because unused page structures are excluded from this dump. NODE 0 ZONE NAME SIZE FREE MEM_MAP START_PADDR START_MAPNR 0 DMA 4095 3934 ffffea0000000038 1000 0 AREA SIZE FREE_AREA_STRUCT BLOCKS PAGES 0 4k ffff880000013068 2 2 ... crash> kmem -i PAGES TOTAL PERCENTAGE TOTAL MEM 128008147 488.3 GB ---- FREE 127599276 486.8 GB 99% of TOTAL MEM USED 408871 1.6 GB 0% of TOTAL MEM SHARED 11049 43.2 MB 0% of TOTAL MEM BUFFERS 5722 22.4 MB 0% of TOTAL MEM CACHED 44638 174.4 MB 0% of TOTAL MEM SLAB 62139 242.7 MB 0% of TOTAL MEM TOTAL SWAP 4893032 18.7 GB ---- SWAP USED 0 0 0% of TOTAL SWAP SWAP FREE 4893032 18.7 GB 100% of TOTAL SWAP Note: 1970727 free pages not found (excluded); results are incomplete. Unused page structures are excluded from this dump. -Cliff Wickman cpw@xxxxxxx -- Crash-utility mailing list Crash-utility@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/crash-utility
