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    SubjectRe: [PATCH] barrier patch set
    On Saturday 20 of March 2004 18:10, Chris Mason wrote:
    > On Sat, 2004-03-20 at 12:05, Bartlomiej Zolnierkiewicz wrote:
    > > On Saturday 20 of March 2004 17:32, Chris Mason wrote:
    > > > On Sat, 2004-03-20 at 11:23, Bartlomiej Zolnierkiewicz wrote:
    > > > > > > - why are we doing pre-flush?
    > > >
    > > > The journaled filesystems need this. We need to make sure that before
    > > > we write the commit block for a transaction, all the previous log
    > > > blocks we're written are safely on media. Then we also need to make
    > > > sure the commit block is on media.
    > >
    > > For low-level driver it shouldn't really matter whether sectors to be
    > > written are the commit block for a transaction or the previous log blocks
    > > and in the current implementation it does matter.
    > As Jens said, it depends on how you define barrier ;-) I define it as
    > this io will be written after all the previous io and before any later
    > io. It was originally written with scsi tags in mind as well, the FS
    > side was the same for both.

    Yes, thanks for explaining this.

    I took a quick look at fs/jbd/ and now I think I understand the way barriers
    currently work. I assume that SCSI handles barriers by ordered tags, right?

    > In the end, I'm not that picky though, any reasonable setup that gets
    > the blocks on media is fine.



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