[Lustre-devel] read ahead

[chas williams - CONTRACTOR]

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  
>accept.

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.