Hi Joel... On Mon, Oct 26, 2009 at 4:33 AM, Joel Fernandes <agnel.joel@xxxxxxxxx> wrote: > In data=ordered mode the ext3_ordered_commit_write function marks the > buffers as dirty, how then does the JBD ensure that the data is > written before the metadata? Once the data buffers are marked as > dirty, JBD doesn't have control anymore over when the data is written > is actually written to disk right? Because the actually writing of the > data is handled by the page wtriteback mechanism (pdflush) right? I am not an expert, but here's my thought: I think writing to backing device is not done simply marking the buffer/page cache dirty. So, I think what kernel does is first prepare an I/O queue to update ext3 journal. Since we talk about data=ordered here, only metadata are logged. Perhaps the key here is, metadata writing is done as a async completion handler of data writing handler. Thus, data is written first, followed by metadata logging Another possibility is composing a single atomic I/O writing request, composed of data writing and metadata logging. Thus, I/O scheduler won't be able to re-order the request and must complete the sequence as we prepared. -- regards, Mulyadi Santosa Freelance Linux trainer and consultant blog: the-hydra.blogspot.com training: mulyaditraining.blogspot.com -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
