On Tue 29-11-11 21:09:02, Wu Fengguang wrote: > If the file size is 20kb and readahead request is [0, 16kb), > it's better to expand the readahead request to [0, 20kb), which will > likely save one followup I/O for [16kb, 20kb). > > If the readahead request already covers EOF, trimm it down to EOF. > Also don't set the PG_readahead mark to avoid an unnecessary future > invocation of the readahead code. > > This special handling looks worthwhile because small to medium sized > files are pretty common. > > Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx> > --- > mm/readahead.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > --- linux-next.orig/mm/readahead.c 2011-11-29 11:28:56.000000000 +0800 > +++ linux-next/mm/readahead.c 2011-11-29 11:29:05.000000000 +0800 > @@ -251,8 +251,16 @@ unsigned long max_sane_readahead(unsigne > unsigned long ra_submit(struct file_ra_state *ra, > struct address_space *mapping, struct file *filp) > { > + pgoff_t eof = ((i_size_read(mapping->host)-1) >> PAGE_CACHE_SHIFT) + 1; > + pgoff_t start = ra->start; > int actual; > > + /* snap to EOF */ > + if (start + ra->size + ra->size / 2 > eof) { > + ra->size = eof - start; > + ra->async_size = 0; > + } > + > actual = __do_page_cache_readahead(mapping, filp, > ra->start, ra->size, ra->async_size); Hmm, wouldn't it be cleaner to do this already in ondemand_readahead()? All other updates of readahead window seem to be there. Also shouldn't we take maximum readahead size into account? Reading 3/2 of max readahead window seems like a relatively big deal for large files... Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html