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Date: Mon, 5 Oct 2009 21:51:25 +0800 From: Wu Fengguang <fengguang.wu@...el.com> To: "Myklebust, Trond" <Trond.Myklebust@...app.com> Cc: "jens.axboe@...cle.com" <jens.axboe@...cle.com>, Chris Mason <chris.mason@...cle.com>, Andrew Morton <akpm@...ux-foundation.org>, "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, "linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org> Subject: Re: [PATCH v2] NFS: introduce writeback wait queue On Mon, Oct 05, 2009 at 07:01:10PM +0800, Myklebust, Trond wrote: > On Oct 5, 2009, at 3:11, "Wu Fengguang" <fengguang.wu@...el.com> wrote: > > > Hi all, > > > > This version makes two standalone functions for easier reuse. > > > > Before patch, nr_writeback is near 1G on my 2GB laptop: > > > > nr_writeback nr_dirty nr_unstable > > 203994 2 154469 > > 203994 2 154469 > > > > After patch, nr_writeback is limited to nfs_congestion_kb=42MB. > > > > nr_writeback nr_dirty nr_unstable > > 11180 34195 11754 > > 9865 36821 8234 > > 10137 36695 9338 > > > > One minor problem I noticed is, NFS writeback is not very smooth. > > This per 0.1s sampled trace shows that it can sometimes stuck for > > up to 0.5s: > > > > nr_writeback nr_dirty nr_unstable > > 11055 37408 9599 > > 10311 37315 10529 > > 10869 35920 11459 > > 10869 35920 11459 > > 10869 35920 11459 > > 10869 35920 11459 > > 10869 35920 11459 > > 10838 35891 10042 > > 10466 35891 10414 > > 10900 34744 11437 > > 10249 34744 12088 > > 10249 34744 12088 > > 10249 34744 12088 > > 10249 34744 12088 > > 10249 34744 12088 > > 10249 34744 12088 > > 10133 34743 10663 > > 10505 34743 11035 > > 10970 34991 11345 > > 10691 34991 11593 > > 10691 34991 11593 > > 10691 34991 11593 > > 10691 34991 11593 > > 10691 34991 11593 > > > > Trond, I guess nr_writeback/nr_unstable are decreased in async RPC > > "complete" events. It is understandable that nr_dirty can sometimes > > stuck on local waits, but the "local determined" nr_dirty and "remote > > determined" nr_writeback/nr_unstable tend to stuck at the same time? > > Did I miss something (that could be obvious to you)? > > It looks (at 7am in the morning after getting up at 4:30am) as though Wow early bird! > the number of unstable pages is remaining constant, which would mean > that we're sending a lot of COMMIT requests (see nfsstat). Since > COMMIT is essentially an fsync call, it means that the server is going > to be slower. Here are the numbers: Client nfs v3: null getattr setattr lookup access readlink 0 0% 18007 3% 67 0% 1752 0% 2499 0% 109 0% read write create mkdir symlink mknod 1742 0% 518695 95% 77 0% 0 0% 0 0% 2 0% remove rmdir rename link readdir readdirplus 104 0% 0 0% 30 0% 40 0% 15 0% 178 0% fsstat fsinfo pathconf commit 140 0% 2 0% 1 0% 2461 0% Server nfs v3: null getattr setattr lookup access readlink 2 0% 18000 3% 67 0% 1752 0% 2495 0% 109 0% read write create mkdir symlink mknod 1742 0% 518695 95% 77 0% 0 0% 0 0% 2 0% remove rmdir rename link readdir readdirplus 104 0% 0 0% 30 0% 40 0% 15 0% 178 0% fsstat fsinfo pathconf commit 140 0% 3 0% 1 0% 2461 0% I noticed that dd often sleep in nfs_updatepage/nfs_wait_on_request, is it because it's doing 512byte writes and thus have to wait on subsequent in-page writes? I guess this may hurt performance on big network latency? [ 268.020588] dd D ffff880002735460 2608 3688 3534 0x00000000 [ 268.020588] ffff8800777c3a38 0000000000000046 0000000000000000 ffff880002735460 [ 268.020588] 000000000000e388 ffff8800777c3fd8 ffff8800775346e0 ffffffff8192c8e0 [ 268.020588] ffff880077534a68 0000000000000082 00000000ffffc9fb ffff8800061d4758 [ 268.020588] Call Trace: [ 268.020588] [<ffffffff8109365d>] ? trace_hardirqs_on+0xd/0x10 [ 268.020588] [<ffffffff8123dc7a>] nfs_wait_bit_killable+0x2a/0x40 [ 268.020588] [<ffffffff81695a82>] __wait_on_bit+0x62/0x90 [ 268.020588] [<ffffffff8123dc50>] ? nfs_wait_bit_killable+0x0/0x40 [ 268.020588] [<ffffffff8123dc50>] ? nfs_wait_bit_killable+0x0/0x40 [ 268.020588] [<ffffffff81695b29>] out_of_line_wait_on_bit+0x79/0x90 [ 268.020588] [<ffffffff8107e2f0>] ? wake_bit_function+0x0/0x50 [ 268.020588] [<ffffffff81243aef>] nfs_wait_on_request+0x2f/0x40 [ 268.020588] [<ffffffff812490a6>] nfs_updatepage+0x2e6/0x540 [ 268.020588] [<ffffffff81239dc2>] nfs_write_end+0x62/0x2c0 [ 268.020588] [<ffffffff810fd469>] generic_file_buffered_write+0x179/0x2a0 [ 268.020588] [<ffffffff810935f5>] ? trace_hardirqs_on_caller+0x155/0x1b0 [ 268.020588] [<ffffffff810fd99d>] __generic_file_aio_write+0x26d/0x440 [ 268.020588] [<ffffffff810fdbbe>] ? generic_file_aio_write+0x4e/0xd0 [ 268.020588] [<ffffffff810fdbd4>] generic_file_aio_write+0x64/0xd0 [ 268.020588] [<ffffffff8123ae66>] nfs_file_write+0x136/0x210 [ 268.020588] [<ffffffff8114d1e9>] do_sync_write+0xf9/0x140 [ 268.020588] [<ffffffff8107e2b0>] ? autoremove_wake_function+0x0/0x40 [ 268.020588] [<ffffffff8111905c>] ? might_fault+0x5c/0xb0 [ 268.020588] [<ffffffff8114de3f>] vfs_write+0xcf/0x1c0 [ 268.020588] [<ffffffff8114e035>] sys_write+0x55/0x90 [ 268.020588] [<ffffffff8100c0b2>] system_call_fastpath+0x16/0x1b Thanks, Fengguang -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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