Re: Background memory scrubbing
From: Rik van Riel
Date: Wed Apr 20 2011 - 13:53:53 EST
On 04/20/2011 01:05 PM, Robert Whitton wrote:
On Wed 20/04/11 6:45 PM , Rik van Riel<riel@xxxxxxxxxx> wrote:
On 04/20/2011 03:58 AM, Robert Whitton wrote:
for each PFN from 256 to the highest valid PFN
{
if (pfn_valid(PFN))
{
page = pfn_to_page(PFN)
va = kmap(page)
atomic_scrub(va, PAGE_SIZE)
kunmap(page)
}
sleep(for_a_while)
}
What exactly does atomic_scrub do?
atomic_scrub is part of the edac subsystem see arch/x86/include/asm/edac.h. It simply does a locked add of zero to each DWORD in the specified range.
I can think of only a few ways in which that could cause a
kernel page fault.
One of the more obvious causes would be running into an
area of kernel memory that is mapped read-only. Writing
to a page that is mapped read-only would cause a page
fault :)
Walking the page tables to check whether my guess is correct
should be possible in the current context. Look at current->mm->pgd for
the page directory and start walking from there.
Incidentally, the kernel mappings should be the same for any
process, so the above should hold true from any context.
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