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authorOlaf Hering <olaf@aepfle.de>2011-05-26 16:25:54 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2011-05-26 17:12:37 -0700
commit997c136f518c5debd63847e78e2a8694f56dcf90 (patch)
treeac2ff48901be3e6834757675dcc177732e034a9f /drivers
parent98bc93e505c03403479c6669c4ff97301cee6199 (diff)
downloadvexpress-lsk-997c136f518c5debd63847e78e2a8694f56dcf90.tar.gz
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 <olaf@aepfle.de> Cc: Alexey Dobriyan <adobriyan@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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