On 2010-07-28, at 10:43, Arifa Nisar wrote: > I am trying to educate myself on prefetching/readahead algorithm for > Lustre's read. For a starter I only have two simple questions. > > 1 - Does Lustre detect linear or random I/O pattern or it always triggers > readahead?
The current algorithm detects sequential and strided read patterns. > 2 - If readahead is triggered, how many pages are read in addition to what > is necessary? It is variable based on how long the same pattern was repeating and the number of pages per request. I would be happy to have you look at the strided readahead detection code more closely, since I suspect it would not correctly detect stride patterns with odd byte size and offset vs. stride patterns with full-page size and offset. We disussed a while ago to rewrite the readahead code to be layered better on the client, but haven't had time to work on it yet. Cheers, Andreas -- Andreas Dilger Lustre Technical Lead Oracle Corporation Canada Inc. _______________________________________________ Lustre-discuss mailing list Lustre-discuss@lists.lustre.org http://lists.lustre.org/mailman/listinfo/lustre-discuss
