The patch titled
readahead: add blk_run_backing_dev
has been added to the -mm tree. Its filename is
readahead-add-blk_run_backing_dev.patch
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*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find
out what to do about this
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: readahead: add blk_run_backing_dev
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)
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>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/readahead.c | 10 ++++++++++
1 file changed, 10 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 +547,15 @@ 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);
_
Patches currently in -mm which might be from hifumi.hisashi@xxxxxxxxxxxxx are
linux-next.patch
readahead-add-blk_run_backing_dev.patch
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