On Wed, Aug 22, 2012 at 11:40:33AM -0400, Rik van Riel wrote:

On 08/21/2012 11:40 PM, Shaohua Li wrote:

quoted

.fault now can retry. The retry can break state machine of .fault. In
filemap_fault, if page is miss, ra->mmap_miss is increased. In the second try,
since the page is in page cache now, ra->mmap_miss is decreased. And these are
done in one fault, so we can't detect random mmap file access.

Add a new flag to indicate .fault is tried once. In the second try, skip
ra->mmap_miss decreasing. The filemap_fault state machine is ok with it.

quoted

Index: linux/arch/avr32/mm/fault.c
===================================================================

--- linux.orig/arch/avr32/mm/fault.c	2012-08-22 09:51:23.035526683 +0800
+++ linux/arch/avr32/mm/fault.c	2012-08-22 09:52:22.822775020 +0800

@@ -152,6 +152,7 @@ good_area:
 			tsk->min_flt++;
 		if (fault & VM_FAULT_RETRY) {
 			flags &= ~FAULT_FLAG_ALLOW_RETRY;
+			flags |= FAULT_FLAG_TRIED;

Is there any place where you set FAULT_FLAG_TRIED
where FAULT_FLAG_ALLOW_RETRY is not cleared?

In other words, could we use the absence of the
FAULT_FLAG_ALLOW_RETRY as the test, avoiding the
need for a new bit flag?

There are still several archs (~7) don't enable fault retry yet. For such
archs, FAULT_FLAG_ALLOW_RETRY isn't set in the first try. If all archs support
fault retry, the new flag is unnecessary.

Thanks,
Shaohua

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