generic/224 triggers infinite "page discard on page xxx" on 512 block size XFS with 4.8-rc1 kernel

[Dave Chinner]

On Sat, Aug 13, 2016 at 03:38:39PM +0800, Eryu Guan wrote:
> Hi all,
> 
> I've hit generic/224 flooding dmesg on 512 block size XFS, 4.8-rc1
> kernel, with the following message:
> 
> ...
> [   98.146091] XFS (sda6): page discard on page ffffea0002f7e780, inode 0xe3a87, offset 1085214720.
> [   98.147431] XFS (sda6): page discard on page ffffea00023c3800, inode 0xe3a87, offset 1085218816.
> [   98.148743] XFS (sda6): page discard on page ffffea0002247700, inode 0xe3a87, offset 1085222912.
> [   98.150136] XFS (sda6): page discard on page ffffea0002f8d000, inode 0xe3a87, offset 1085227008.
> [   98.151496] XFS (sda6): page discard on page ffffea0002c58840, inode 0xe3a87, offset 1085231104.
> [   98.152794] XFS (sda6): page discard on page ffffea0002e65340, inode 0xe3a87, offset 1085235200.
> ...
> 
> The inode number is always the same, only the page address and offset
> are changing.
> 
> This is triggered by this dd command in generic/224:
> 
> dd if=/dev/zero of=$SCRATCH_MNT/testfile.$i bs=4k conv=notrunc
> 
> and it won't return until you kill it.

It's not infinite. It just does it for every page and 1000 processes
all trying to write 256,000 pages is a lot.... We have a fix
pending for it and I'm aiming to get it to Linus later this week.

Cheers,

Dave.
-- 
Dave Chinner
david at fromorbit.com