Re: [PATCH 06/15] readahead: replace ra->mmap_miss with ra->ra_flags

[Rik van Riel]

On 02/23/2010 10:10 PM, Wu Fengguang wrote:
> Introduce a readahead flags field and embed the existing mmap_miss in it
> (mainly to save space).
>
> It also changes the mmap_miss upper bound from LONG_MAX to 4096.
> This is to help adapt properly for changing mmap access patterns.
>
> It will be possible to lose the flags in race conditions, however the
> impact should be limited.  For the race to happen, there must be two
> threads sharing the same file descriptor to be in page fault or
> readahead at the same time.
>
> Note that it has always been racy for "page faults" at the same time.
>
> And if ever the race happen, we'll lose one mmap_miss++ or mmap_miss--.
> Which may change some concrete readahead behavior, but won't really
> impact overall I/O performance.
>
> CC: Nick Piggin<npiggin@xxxxxxx>
> CC: Andi Kleen<andi@xxxxxxxxxxxxxx>
> CC: Steven Whitehouse<swhiteho@xxxxxxxxxx>
> Signed-off-by: Wu Fengguang<fengguang.wu@xxxxxxxxx>

Acked-by: Rik van Riel <riel@xxxxxxxxxx>
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