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>
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