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Date: Mon, 7 Jul 2014 17:13:49 -0400
From: Benjamin LaHaise <bcrl@...ck.org>
To: linux-ext4@...r.kernel.org
Subject: ext4: first write to large ext3 filesystem takes 96 seconds
Hi folks,
I've just ran into a bug with the ext4 codebase in 3.4.91 that doesn't seem
to exist in ext3, and was wondering if anyone has encountered this before.
I have a 7.4TB ext3 filesystem that has been filled with 1.8TB of data.
When this filesystem is freshly mounted, the first write to the filesystem
takes a whopping 96 seconds to complete, during which time the system is
reading about 1000 blocks per second. Subsequent writes are much quicker.
The problem seems to be that ext4 is loading all of the bitmaps on the
filesystem before the first write proceeds. The backtrace looks roughly as
follows:
[ 4480.921288] [<ffffffff81437472>] ? dm_request_fn+0x112/0x1c0
[ 4480.921292] [<ffffffff81244bf5>] ? __blk_run_queue+0x15/0x20
[ 4480.921294] [<ffffffff81246670>] ? queue_unplugged+0x20/0x50
[ 4480.921297] [<ffffffff8154ed05>] schedule+0x45/0x60
[ 4480.921299] [<ffffffff8154ef7c>] io_schedule+0x6c/0xb0
[ 4480.921301] [<ffffffff810fb7a9>] sleep_on_buffer+0x9/0x10
[ 4480.921303] [<ffffffff8154d435>] __wait_on_bit+0x55/0x80
[ 4480.921306] [<ffffffff810fb7a0>] ? unmap_underlying_metadata+0x40/0x40
[ 4480.921308] [<ffffffff810fb7a0>] ? unmap_underlying_metadata+0x40/0x40
[ 4480.921310] [<ffffffff8154d4d8>] out_of_line_wait_on_bit+0x78/0x90
[ 4480.921312] [<ffffffff8104d5b0>] ? autoremove_wake_function+0x40/0x40
[ 4480.921315] [<ffffffff810fb756>] __wait_on_buffer+0x26/0x30
[ 4480.921318] [<ffffffff81146258>] ext4_wait_block_bitmap+0x138/0x190
[ 4480.921321] [<ffffffff8116c816>] ext4_mb_init_cache+0x1e6/0x5f0
[ 4480.921324] [<ffffffff8109654a>] ? add_to_page_cache_locked+0x9a/0xd0
[ 4480.921327] [<ffffffff810965b1>] ? add_to_page_cache_lru+0x31/0x50
[ 4480.921330] [<ffffffff8116cd1f>] ext4_mb_init_group+0xff/0x1e0
[ 4480.921332] [<ffffffff8116ce9f>] ext4_mb_good_group+0x9f/0x130
[ 4480.921334] [<ffffffff8116e41f>] ext4_mb_regular_allocator+0x1bf/0x3d0
[ 4480.921337] [<ffffffff8116c0ac>] ? ext4_mb_normalize_request+0x26c/0x4d0
[ 4480.921339] [<ffffffff811716ce>] ext4_mb_new_blocks+0x2ee/0x490
[ 4480.921342] [<ffffffff81174c11>] ? ext4_get_branch+0x101/0x130
[ 4480.921345] [<ffffffff8117639c>] ext4_ind_map_blocks+0x9bc/0xc10
[ 4480.921347] [<ffffffff810fae11>] ? __getblk+0x21/0x2b0
[ 4480.921350] [<ffffffff8114c9a3>] ext4_map_blocks+0x293/0x390
[ 4480.921353] [<ffffffff8117a462>] ? do_get_write_access+0x1d2/0x450
[ 4480.921355] [<ffffffff810cb0b4>] ? kmem_cache_alloc+0xa4/0xc0
[ 4480.921358] [<ffffffff8114d9e9>] _ext4_get_block+0xa9/0x140
[ 4480.921360] [<ffffffff8114dab1>] ext4_get_block+0x11/0x20
[ 4480.921362] [<ffffffff810fbda5>] __block_write_begin+0x2b5/0x470
[ 4480.921365] [<ffffffff8114daa0>] ? noalloc_get_block_write+0x20/0x20
[ 4480.921368] [<ffffffff81096679>] ? grab_cache_page_write_begin+0xa9/0x100
[ 4480.921370] [<ffffffff8114c1e2>] ext4_write_begin+0x132/0x2f0
[ 4480.921373] [<ffffffff81095869>] generic_file_buffered_write+0x119/0x260
[ 4480.921376] [<ffffffff81096eef>] __generic_file_aio_write+0x27f/0x430
[ 4480.921379] [<ffffffff810cfbba>] ? do_huge_pmd_anonymous_page+0x1ea/0x2d0
[ 4480.921382] [<ffffffff81097101>] generic_file_aio_write+0x61/0xc0
[ 4480.921384] [<ffffffff81147c18>] ext4_file_write+0x68/0x2a0
[ 4480.921387] [<ffffffff8154e723>] ? __schedule+0x2c3/0x800
[ 4480.921389] [<ffffffff810d2a41>] do_sync_write+0xe1/0x120
[ 4480.921392] [<ffffffff8154eefa>] ? _cond_resched+0x2a/0x40
[ 4480.921395] [<ffffffff810d31c9>] vfs_write+0xc9/0x170
[ 4480.921397] [<ffffffff810d3910>] sys_write+0x50/0x90
[ 4480.921400] [<ffffffff8155155f>] sysenter_dispatch+0x7/0x1a
Any thoughts? Have there been any changes to this area of the ext4 code?
-ben
--
"Thought is the essence of where you are now."
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