Re: [RFD] BIO_RW_BARRIER - what it means for devices, filesystems, and dm/md.

The order that these are expected by the filesystem to hit stable
storage are:

1. block 4 and 10 on stable storage in any order
2. barrier block X on stable storage
3. block 5 and 20 on stable storage in any order

The point I'm trying to make is that in XFS,  block 5 and 20 cannot
be allowed to hit the disk before the barrier block because they
have strict order dependency on block X being stable before them,
just like block X has strict order dependency that block 4 and 10
must be stable before we start the barrier block write.

That would be the exactly how I understand Documentation/block/barrier.txt:

"In other words, I/O barrier requests have the following two properties.
1. Request ordering
...
2. Forced flushing to physical medium"

"So, I/O barriers need to guarantee that requests actually get written
to non-volatile medium in order."

Stefan
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• References:
  • [RFD] BIO_RW_BARRIER - what it means for devices, filesystems, and dm/md.
    • From: Neil Brown <[email protected]>
  • Re: [RFD] BIO_RW_BARRIER - what it means for devices, filesystems, and dm/md.
    • From: Neil Brown <[email protected]>
  • Re: [RFD] BIO_RW_BARRIER - what it means for devices, filesystems, and dm/md.
    • From: David Chinner <[email protected]>
  • Re: [RFD] BIO_RW_BARRIER - what it means for devices, filesystems, and dm/md.
    • From: Phillip Susi <[email protected]>
  • Re: [RFD] BIO_RW_BARRIER - what it means for devices, filesystems, and dm/md.
    • From: David Chinner <[email protected]>
  • Re: [RFD] BIO_RW_BARRIER - what it means for devices, filesystems, and dm/md.
    • From: [email protected]
  • Re: [RFD] BIO_RW_BARRIER - what it means for devices, filesystems, and dm/md.
    • From: David Chinner <[email protected]>

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