From: Olaf Hering Date: Thu, 26 May 2011 23:25:54 +0000 (-0700) Subject: fs/proc/vmcore.c: add hook to read_from_oldmem() to check for non-ram pages X-Git-Tag: v3.0-rc1~74 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=997c136f518c5debd63847e78e2a8694f56dcf90;p=pandora-kernel.git fs/proc/vmcore.c: add hook to read_from_oldmem() to check for non-ram pages The balloon driver in a Xen guest frees guest pages and marks them as mmio. When the kernel crashes and the crash kernel attempts to read the oldmem via /proc/vmcore a read from ballooned pages will generate 100% load in dom0 because Xen asks qemu-dm for the page content. Since the reads come in as 8byte requests each ballooned page is tried 512 times. With this change a hook can be registered which checks wether the given pfn is really ram. The hook has to return a value > 0 for ram pages, a value < 0 on error (because the hypercall is not known) and 0 for non-ram pages. This will reduce the time to read /proc/vmcore. Without this change a 512M guest with 128M crashkernel region needs 200 seconds to read it, with this change it takes just 2 seconds. Signed-off-by: Olaf Hering Cc: Alexey Dobriyan Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Reading git-diff-tree failed