On Fri, Jun 3, 2011 at 4:55 AM, Matthew Wilcox <willy@xxxxxxxxxxxxxxx> wrote: > The exact definition of PageReadahead doesn't seem to be documented > anywhere. ÂI'm assuming it means "This page was not directly requested; > it is being read for prefetching purposes", exactly like the READA > semantics. > > If my interpretation is correct, then the implementation in > __do_page_cache_readahead is wrong: > > Â Â Â Â Â Â Â Âif (page_idx == nr_to_read - lookahead_size) > Â Â Â Â Â Â Â Â Â Â Â ÂSetPageReadahead(page); > > It'll only set the PageReadahead bit on one page. ÂThe patch below fixes > this ... if my understanding is correct. Incorrect I believe: it's a trigger to say, when you get this far, it's time to think about kicking off the next read. > > If my understanding is wrong, then how are readpage/readpages > implementations supposed to know that the VM is only prefetching these > pages, and they're not as important as metadata (dependent) reads? I don't think they do know at present; but I can well imagine there may be advantage in them knowing. Hugh -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href