On Thu, May 21, 2009 at 02:01:47PM +0800, Hisashi Hifumi wrote: > > At 11:51 09/05/20, Wu Fengguang wrote: > >On Mon, May 18, 2009 at 07:53:00PM +0200, Jens Axboe wrote: > >> On Mon, May 18 2009, Hisashi Hifumi wrote: > >> > Hi. > >> > > >> > I wrote a patch that adds blk_run_backing_dev on page_cache_async_readahead > >> > so readahead I/O is unpluged to improve throughput. > >> > > >> > 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 > >> > > >> > Sequential read performance on a big file was improved. > >> > Please merge my patch. > >> > > >> > Thanks. > >> > > >> > Signed-off-by: Hisashi Hifumi <hifumi.hisashi@xxxxxxxxxxxxx> > >> > > >> > diff -Nrup linux-2.6.30-rc6.org/mm/readahead.c > >linux-2.6.30-rc6.unplug/mm/readahead.c > >> > --- linux-2.6.30-rc6.org/mm/readahead.c 2009-05-18 10:46:15.000000000 +0900 > >> > +++ linux-2.6.30-rc6.unplug/mm/readahead.c 2009-05-18 > >13:00:42.000000000 +0900 > >> > @@ -490,5 +490,7 @@ page_cache_async_readahead(struct addres > >> > > >> > /* do read-ahead */ > >> > ondemand_readahead(mapping, ra, filp, true, offset, req_size); > >> > + > >> > + blk_run_backing_dev(mapping->backing_dev_info, NULL); > >> > } > >> > EXPORT_SYMBOL_GPL(page_cache_async_readahead); > >> > >> I'm surprised this makes much of a difference. It seems correct to me to > >> NOT unplug the device, since it will get unplugged when someone ends up > >> actually waiting for a page. And that will then kick off the remaining > >> IO as well. For this dd case, you'll be hitting lock_page() for the > >> readahead page really soon, definitely not long enough to warrant such a > >> big difference in speed. > > > >The possible timing change of this patch is (assuming readahead size=100): > > > >T0 read(100), which triggers readahead(200, 100) > >T1 read(101) > >T2 read(102) > >... > >T100 read(200), find_get_page(200) => readahead(300, 100) > > lock_page(200) => implicit unplug > > > >The readahead(200, 100) submitted at time T0 *might* be delayed to the > >unplug time of T100. > > > >But that is only a possibility. In normal cases, the read(200) would > >be blocking and there will be a lock_page(200) that will immediately > >unplug device for readahead(300, 100). > > > Hi Andrew. > Following patch improves sequential read performance and does not harm > other performance. > Please merge my patch. > Comments? > Thanks. > > #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 > > Signed-off-by: Hisashi Hifumi <hifumi.hisashi@xxxxxxxxxxxxx> > > diff -Nrup linux-2.6.30-rc6.org/mm/readahead.c linux-2.6.30-rc6.unplug/mm/readahead.c > --- linux-2.6.30-rc6.org/mm/readahead.c 2009-05-18 10:46:15.000000000 +0900 > +++ linux-2.6.30-rc6.unplug/mm/readahead.c 2009-05-18 13:00:42.000000000 +0900 > @@ -490,5 +490,7 @@ page_cache_async_readahead(struct addres > > /* do read-ahead */ > ondemand_readahead(mapping, ra, filp, true, offset, req_size); > + > + blk_run_backing_dev(mapping->backing_dev_info, NULL); > } > EXPORT_SYMBOL_GPL(page_cache_async_readahead); > > Hi Hisashi, I wonder if the following updated patch can achieve the same performance. Can you try testing this out? Thanks, Fengguang --- diff --git a/mm/readahead.c b/mm/readahead.c index 133b6d5..fd3df66 100644 --- a/mm/readahead.c +++ b/mm/readahead.c @@ -490,5 +490,8 @@ page_cache_async_readahead(struct address_space *mapping, /* do read-ahead */ ondemand_readahead(mapping, ra, filp, true, offset, req_size); + + 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
