Messages in this thread | | | From | Bartlomiej Zolnierkiewicz <> | Subject | Re: [PATCH] barrier patch set | Date | Sat, 20 Mar 2004 21:16:57 +0100 |
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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.
Yep.
Regards, Bartlomiej
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