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    SubjectRe: [PATCH 06/15] readahead: replace ra->mmap_miss with ra->ra_flags
    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@suse.de>
    > CC: Andi Kleen<andi@firstfloor.org>
    > CC: Steven Whitehouse<swhiteho@redhat.com>
    > Signed-off-by: Wu Fengguang<fengguang.wu@intel.com>

    Acked-by: Rik van Riel <riel@redhat.com>


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