On Thu, 2009-08-27 at 12:49 +0300, Boaz Harrosh wrote: > On 08/27/2009 09:34 AM, Martin K. Petersen wrote: > >>>>>> "Boaz" == Boaz Harrosh <bharrosh@xxxxxxxxxxx> writes: > > > > Boaz> I know that we also have the above problem with iscsi and > > Boaz> data-digest such that when we come to sign the data it might > > Boaz> change on us before the target receives it. > > > > Yep, I have the same problem. I talked to Andrew Morton a couple of > > months ago and he said that modifying pages in flight is "a feature" as > > far as ext[234] is concerned. > > > > As you might know, I have a filesystem copied from the ext2 code base. > I'm experimenting with altering the behavior so that pages written to > while been IOed will page fault, then sleep, until IO is done. > Clearly this is a good "feature" until such systems like mirror or signed- > data that are forced to reallocate-copy all IO do to the 2% optimization > that thing gives you. What about reads to the page? If you allow them, you get the situation where something signals a write intent, tries to write and gets put into wait, then the readers get the old data still. > At the final outcome I hope for a VFS support on a flip of a flag or > something. So under laying device can turn that "feature" off when it > means grate performance gains in it's operations. > > If any one has thought about that problem, and as some preliminary strategies, > please I'm all hears. I've just started on this subject and currently I do not > have a clue. The correct way to handle this is simply to dump the page being written. It's dirty and was updated after the last write attempt, so it gets re-written out. It costs nothing and it's incredibly fast. What you likely want is a way of telling that the page got re-written so you don't need to print out scary warning messages about parity problems. James -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
