[Lustre-devel] read ahead

chas williams - CONTRACTOR chas at cmf.nrl.navy.mil
Thu Dec 13 07:15:53 PST 2007

In message <6C95C14E-9F4E-4E3E-A435-5010C2EFC999 at sun.com>,Oleg Drokin writes:
>Yes it is.
>DIRECT IO by it's nature is "direct", i.e. it gets straight into  
>application buffers,
>we are not to put any more data there than application said it can  

i agree with this interpretation of O_DIRECT.

>And we are not allowed to cache any of that data (or to use any cache  
>to get
>the data during reads) too.

this seems a bit stricter than i would expect.  while i would expect
O_DIRECT to bypass the kernel readahead mechanism, i think that lustre's
readahead is outside of the scope of O_DIRECT.

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