> Hi Andrew. > Please merge following patch. > Thanks. > > --- > > I added blk_run_backing_dev on page_cache_async_readahead > so readahead I/O is unpluged to improve throughput on > especially RAID environment. > > Following is the test result with dd. > > #dd if=testdir/testfile of=/dev/null bs=16384 > > -2.6.30-rc6 > 1048576+0 records in > 1048576+0 records out > 17179869184 bytes (17 GB) copied, 224.182 seconds, 76.6 MB/s > > -2.6.30-rc6-patched > 1048576+0 records in > 1048576+0 records out > 17179869184 bytes (17 GB) copied, 206.465 seconds, 83.2 MB/s > > My testing environment is as follows: > Hardware: HP DL580 > CPU:Xeon 3.2GHz *4 HT enabled > Memory:8GB > Storage: Dothill SANNet2 FC (7Disks RAID-0 Array) > > The normal case is, if page N become uptodate at time T(N), then > T(N) <= T(N+1) holds. With RAID (and NFS to some degree), there > is no strict ordering, the data arrival time depends on > runtime status of individual disks, which breaks that formula. So > in do_generic_file_read(), just after submitting the async readahead IO > request, the current page may well be uptodate, so the page won't be locked, > and the block device won't be implicitly unplugged: Please attach blktrace analysis ;) > > if (PageReadahead(page)) > page_cache_async_readahead() > if (!PageUptodate(page)) > goto page_not_up_to_date; > //... > page_not_up_to_date: > lock_page_killable(page); > > Therefore explicit unplugging can help. > > Signed-off-by: Hisashi Hifumi <hifumi.hisashi@xxxxxxxxxxxxx> > Acked-by: Wu Fengguang <fengguang.wu@xxxxxxxxx> > > > mm/readahead.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > --- linux.orig/mm/readahead.c > +++ linux/mm/readahead.c > @@ -490,5 +490,15 @@ page_cache_async_readahead(struct addres > > /* do read-ahead */ > ondemand_readahead(mapping, ra, filp, true, offset, req_size); > + > + /* > + * Normally the current page is !uptodate and lock_page() will be > + * immediately called to implicitly unplug the device. However this > + * is not always true for RAID conifgurations, where data arrives > + * not strictly in their submission order. In this case we need to > + * explicitly kick off the IO. > + */ > + if (PageUptodate(page)) > + blk_run_backing_dev(mapping->backing_dev_info, NULL); > } > EXPORT_SYMBOL_GPL(page_cache_async_readahead); > -- 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
