From: Theodore Ts'o <tytso@mit.edu>
Subject: Re: [PATCH 4/5] jbd2: Speedup jbd2_journal_get_[write|undo]_access()
Date: Mon, 8 Jun 2015 18:32:30 -0400
Message-ID: <20150608223230.GO19168@thunk.org>
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 <20150608164726.GM19168@thunk.org>
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To: Jan Kara <jack@suse.cz>
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On Mon, Jun 08, 2015 at 12:47:26PM -0400, Theodore Ts'o wrote:
> On Thu, Apr 02, 2015 at 03:58:19PM +0200, Jan Kara wrote:
> > jbd2_journal_get_write_access() and jbd2_journal_get_create_access() are
> > frequently called for buffers that are already part of the running
> > transaction - most frequently it is the case for bitmaps, inode table
> > blocks, and superblock. Since in such cases we have nothing to do, it is
> > unfortunate we still grab reference to journal head, lock the bh, lock
> > bh_state only to find out there's nothing to do.
> > 
> > Improving this is a bit subtle though since until we find out journal
> > head is attached to the running transaction, it can disappear from under
> > us because checkpointing / commit decided it's no longer needed. We deal
> > with this by protecting journal_head slab with RCU. We still have to be
> > careful about journal head being freed & reallocated within slab and
> > about exposing journal head in consistent state (in particular
> > b_modified and b_frozen_data must be in correct state before we allow
> > user to touch the buffer).
> > 
> > FIXME: Performance data.
> > 
> > Signed-off-by: Jan Kara <jack@suse.cz>
> 
> Applied, so we can start getting some testing on this patch.  Did you
> ever get performance data?

.... and this patch is causing generic/011 to fail.

generic/011 2s ...  [18:26:52][   13.085375] run fstests generic/011 at 2015-06-08 18:26:52
[   13.698245] ------------[ cut here ]------------
[   13.699093] kernel BUG at /usr/projects/linux/ext4/fs/jbd2/transaction.c:1329!
[   13.700354] invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC
[   13.701388] Modules linked in:
[   13.701505] CPU: 0 PID: 3947 Comm: dirstress Not tainted 4.1.0-rc4-00034-g562bef4 #2758
[   13.701505] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[   13.701505] task: ee1bc110 ti: ec080000 task.ti: ec080000
[   13.701505] EIP: 0060:[<c02eeb96>] EFLAGS: 00210206 CPU: 0
[   13.701505] EIP is at jbd2_journal_dirty_metadata+0x5e/0x1da
[   13.701505] EAX: 00000000 EBX: eccde090 ECX: f03fd580 EDX: f03fd580
[   13.701505] ESI: eee85860 EDI: ed918cc0 EBP: ec081e14 ESP: ec081e00
[   13.701505]  DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068
[   13.701505] CR0: 8005003b CR2: b73fbb20 CR3: 2fd58700 CR4: 000006f0
[   13.701505] DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000
[   13.701505] DR6: fffe0ff0 DR7: 00000400
[   13.701505] Stack:
[   13.701505]  000000f7 f03fd580 ed918cc0 eee85860 00000000 ec081e30 c02d7fc8 00001179
[   13.701505]  c0865c3c eae67c30 ee17f800 00000000 ec081e84 c02b6458 00000000 ed918cc0
[   13.701505]  c02ee941 00000000 00000000 00000000 eae67b20 00000000 00000000 eae67e78
[   13.701505] Call Trace:
[   13.701505]  [<c02d7fc8>] __ext4_handle_dirty_metadata+0xd4/0x19d
[   13.701505]  [<c02b6458>] ext4_mark_iloc_dirty+0x458/0x577
[   13.701505]  [<c02ee941>] ? jbd2_journal_get_write_access+0x3d/0x48
[   13.701505]  [<c02b66e4>] ext4_mark_inode_dirty+0x105/0x252
[   13.701505]  [<c02b121b>] __ext4_new_inode+0xcb6/0xe9b
[   13.701505]  [<c02bd87d>] ext4_mknod+0x8b/0x11c
[   13.701505]  [<c025ffbe>] vfs_mknod+0x7e/0x9e
[   13.701505]  [<c0263a0a>] SyS_mknodat+0x119/0x15a
[   13.701505]  [<c0263a65>] SyS_mknod+0x1a/0x1c
[   13.701505]  [<c083292a>] syscall_call+0x7/0x7
[   13.701505] Code: 00 00 8b 5f 24 8b 4b 18 39 d1 74 07 39 53 1c 74 02 0f 0b 83 7b 0c 01 75 14 39 d1 0f 85 7e 01 00 00 83 7b 08 01 0f 84 74 01 00 00 <0f> 0b 8b 02 53 68 16 2c ac c0 68 36 05 00 00 68 14 81 86 c0 68
[   13.701505] EIP: [<c02eeb96>] jbd2_journal_dirty_metadata+0x5e/0x1da SS:ESP 0068:ec081e00
[   13.734150] ---[ end trace eb359de3ec6c3af4 ]---

I will drop 4/5 and 5/5 from this patch series from the ext4 tree for
now.  Could you take a look at this?

      	    	      	    	       	    - Ted