Re: [patch]readahead: fault retry breaks mmap file read random detection

[Rik van Riel <riel@redhat.com>]

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

> 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?

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