[Lustre-devel] read ahead
Nikita Danilov
Nikita.Danilov at Sun.COM
Tue Dec 11 21:53:59 PST 2007
Andreas Dilger writes:
[...]
>
> Two areas where our readahead is lacking are:
> - strided reads (may turn the above 16 x 4kB reads into a situation
> where the client will prefetch pages instead of "random" IO, depending
> on access pattern, and will avoid prefetch of data the client is not
> expecting to use)
> - limiting the readahead to the rate that the client is actually consuming
> it (currently once we detect sequential reads the readahead window grows
> eventually to the maximum even if this is far more than what the client
> needs)
I wonder how useful can inter-file read-ahead be. For example, starting
an executable almost always incurs a sequence of reads of the shared
libraries, compilation re-reads header files in the same order over and
over again, etc.
>
> Cheers, Andreas
Nikita.
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