Messages in this thread | | | Date | Wed, 22 Apr 2009 18:17:32 +0200 | Subject | Re: Question : internal processing of block I/O queue | From | Corrado Zoccolo <> |
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Hi, I think you should read: Documentation/block/barrier.txt Without explicitly asking for barriers, block I/O doesn't guarantee FIFO ordering (or any other ordering), since it would be too inefficient on some devices.
Corrado
On Wed, Apr 22, 2009 at 4:50 PM, <ohyama_sec@ariel-networks.com> wrote: > From: Hiroyasu OHYAMA > > I'm a student of Japan, and I diddle the Linux for joyment. > Could I ask you a question about block I/O. > > The question is that "Does The linux block I/O processing follow a first-in first-out order" > > Now, I'm making layer under low level filesystem. And I wonna make it work as Cache of data like page cache. > I could understood if I emit block I/O request with submit_bio(), the kernel delay it, and I could notice the result by .bi_end_io() method that I set. > > But I have something on my mind. "Does the kernel assure the order of block I/O ?" > > Once I issue a block I/O request to common I/O layer, the I/O processing is delayed. And the actual block I/O processing is executed by kernel thread. > So user who commit block I/O never have to mind the sequence of delayed block I/O requests. > But I want to know that "The block I/O processing executed first is executed earlient, or may not". > > If a I/O request issued back is issued earlier than before, I have to protect the target block that is issued block I/O request. > > Could you please give me the actuall operation of block I/O component, that is "It may happen, or not". > > Thank you in advance. > -- > 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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