[Bugme-janitors] [Bug 22802] New: Freeze in raid condition (sync write)

bugzilla-daemon at bugzilla.kernel.org bugzilla-daemon at bugzilla.kernel.org
Fri Nov 12 07:41:33 PST 2010


https://bugzilla.kernel.org/show_bug.cgi?id=22802

           Summary: Freeze in raid condition (sync write)
           Product: IO/Storage
           Version: 2.5
          Platform: All
        OS/Version: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: Other
        AssignedTo: io_other at kernel-bugs.osdl.org
        ReportedBy: alpha_one_x86 at first-world.info
        Regression: No


Hello, I have 6x Hdd as raid6, with 8GB of memory. I have hdd with problem
reported via smart:
Raw_Read_Error_Rate     0x002f   195   195   051    Pre-fail  Always       -   
   6786
My raid:
md2 : active raid5 sdf2[3] sde2[2] sdd2[5] sdc2[0] sdb2[1] sda2[4]
      97655680 blocks level 5, 64k chunk, algorithm 2 [6/6] [UUUUUU]
md3 : active raid5 sdf3[3] sde3[2] sdd3[5] sdc3[0] sdb3[1] sda3[4]
      24413440 blocks level 5, 64k chunk, algorithm 2 [6/6] [UUUUUU]
md4 : active raid6 sdf4[3] sde4[2] sdd4[5] sdc4[0] sdb4[1] sda4[4]
      5762507008 blocks level 6, 64k chunk, algorithm 2 [6/6] [UUUUUU]
The actual behavior:
Freeze when a application do read (the same file, normally in cache)/write. All
seem be synchron.
Desired behavior:
Never freeze.
How:
Write into buffer and keep running the application, and use the cache before
raid access or without this blocking bug.
I don't know if the kernel cache is for IO (type block), or file then before
the VFS, or both. But this last method should be the best. Because hard reboot
erase all buffer and application, then freeze the application or not, the data
is in memory and will be lost, but multiple write into the same file at the
same place can be grouped in one write, same for near place.

That's highlight other problem:
Gentoo emerge systeme do this kind of manupulation:
1) write file/folder into /tmp (source of software)
2) compile it (mixed read/write)
3) remove it
All comments about gentoo say that's /tmp mounted as tmpfs is really more fast
than ext4/btrfs/... in some case like me where all file manipulation should be
leave in memory.
I don't know if in this case it wait the buffer is writing before resend this
content or directly send at the first read access the buffer content.

I have try touch all key into /sys ... I can do test. But if no have
buffer/cache before VFS should be easy way to optimize linux (and do some
operation like keep socket in memory).

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