Messages in this thread | | | Date | Sun, 6 Nov 2011 20:59:28 -0800 | From | Andy Isaacson <> | Subject | long sleep_on_page delays writing to slow storage |
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I am running 1a67a573b (3.1.0-09125 plus a small local patch) on a Core i7, 8 GB RAM, writing a few GB of data to a slow SD card attached via usb-storage with vfat. I mounted without specifying any options,
/dev/sdb1 /mnt/usb vfat rw,nosuid,nodev,noexec,relatime,uid=22448,gid=22448,fmask=0022,dmask=0022,codepage=cp437,iocharset=utf8,shortname=mixed,errors=remount-ro 0 0
and I'm using rsync to write the data.
We end up in a fairly steady state with a half GB dirty:
Dirty: 612280 kB
The dirty count stays high despite running sync(1) in another xterm.
The bug is,
Firefox (iceweasel 7.0.1-4) hangs at random intervals. One thread is stuck in sleep_on_page
[<ffffffff810c50da>] sleep_on_page+0xe/0x12 [<ffffffff810c525b>] wait_on_page_bit+0x72/0x74 [<ffffffff811030f9>] migrate_pages+0x17c/0x36f [<ffffffff810fa24a>] compact_zone+0x467/0x68b [<ffffffff810fa6a7>] try_to_compact_pages+0x14c/0x1b3 [<ffffffff810cbda1>] __alloc_pages_direct_compact+0xa7/0x15a [<ffffffff810cc4ec>] __alloc_pages_nodemask+0x698/0x71d [<ffffffff810f89c2>] alloc_pages_vma+0xf5/0xfa [<ffffffff8110683f>] do_huge_pmd_anonymous_page+0xbe/0x227 [<ffffffff810e2bf4>] handle_mm_fault+0x113/0x1ce [<ffffffff8102fe3d>] do_page_fault+0x2d7/0x31e [<ffffffff812fe535>] page_fault+0x25/0x30 [<ffffffffffffffff>] 0xffffffffffffffff
And it stays stuck there for long enough for me to find the thread and attach strace. Apparently it was stuck in
1320640739.201474 munmap(0x7f5c06b00000, 2097152) = 0
for something between 20 and 60 seconds.
There's no reason to let a 6MB/sec high latency device lock up 600 MB of dirty pages. I'll have to wait a hundred seconds after my app exits before the system will return to usability.
And there's no way, AFAICS, for me to work around this behavior in userland.
And I don't understand how this compact_zone thing is intended to work in this situation.
edited but nearly full dmesg at http://web.hexapodia.org/~adi/snow/dmesg-3.1.0-09126-g4730284.txt
Thoughts?
Thanks, -andy
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