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On Sat, Mar 20 2004, Bartlomiej Zolnierkiewicz wrote: > 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? That's the idea, yes. Needs some SCSI error handling work though, to always ensure correct ordering. -- Jens Axboe - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | ||||||||||||
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