Subject: Re: [RESEND] [PATCH] readahead:add blk_run_backing_dev Reply-To: In-Reply-To: <20090922135838.33ebe36b.akpm@xxxxxxxxxxxxxxxxxxxx> On Wed, Sep 23, 2009 at 04:58:38AM +0800, Andrew Morton wrote: > On Fri, 29 May 2009 14:35:55 +0900 > Hisashi Hifumi <hifumi.hisashi@xxxxxxxxxxxxx> wrote: > > > I added blk_run_backing_dev on page_cache_async_readahead > > so readahead I/O is unpluged to improve throughput on > > especially RAID environment. > > I still haven't sent this upstream. It's unclear to me that we've > decided that it merits merging? Yes, if I remember it right, the performance gain is later confirmed by Ronald's independent testing on his RAID. (Ronald CC-ed) Thanks, Fengguang > > > From: Hisashi Hifumi <hifumi.hisashi@xxxxxxxxxxxxx> > > I added blk_run_backing_dev on page_cache_async_readahead so readahead I/O > is unpluged to improve throughput on especially RAID environment. > > 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: > > 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. > > 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 > > (7Disks RAID-0 Array) > > -2.6.30-rc6 > 1054976+0 records in > 1054976+0 records out > 17284726784 bytes (17 GB) copied, 212.233 seconds, 81.4 MB/s > > -2.6.30-rc6-patched > 1054976+0 records out > 17284726784 bytes (17 GB) copied, 198.878 seconds, 86.9 MB/s > > (7Disks RAID-5 Array) > > The patch was found to improve performance with the SCST scsi target > driver. See > http://sourceforge.net/mailarchive/forum.php?thread_name=a0272b440906030714g67eabc5k8f847fb1e538cc62%40mail.gmail.com&forum_name=scst-devel > > [akpm@xxxxxxxxxxxxxxxxxxxx: unbust comment layout] > [akpm@xxxxxxxxxxxxxxxxxxxx: "fix" CONFIG_BLOCK=n] > Signed-off-by: Hisashi Hifumi <hifumi.hisashi@xxxxxxxxxxxxx> > Acked-by: Wu Fengguang <fengguang.wu@xxxxxxxxx> > Cc: Jens Axboe <jens.axboe@xxxxxxxxxx> > Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> > Tested-by: Ronald <intercommit@xxxxxxxxx> > Cc: Bart Van Assche <bart.vanassche@xxxxxxxxx> > Cc: Vladislav Bolkhovitin <vst@xxxxxxxx> > Cc: Randy Dunlap <randy.dunlap@xxxxxxxxxx> > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > --- > > mm/readahead.c | 12 ++++++++++++ > 1 file changed, 12 insertions(+) > > diff -puN mm/readahead.c~readahead-add-blk_run_backing_dev mm/readahead.c > --- a/mm/readahead.c~readahead-add-blk_run_backing_dev > +++ a/mm/readahead.c > @@ -547,5 +547,17 @@ page_cache_async_readahead(struct addres > > /* do read-ahead */ > ondemand_readahead(mapping, ra, filp, true, offset, req_size); > + > +#ifdef CONFIG_BLOCK > + /* > + * 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); > +#endif > } > 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
