On Sun 06-06-10 12:35:03, Boaz Harrosh wrote: > On 06/04/2010 07:23 PM, Jan Kara wrote: > > On Thu 03-06-10 19:09:52, Boaz Harrosh wrote: > >> [Topic] > >> How to not let pages change while in IO > >> > >> [Abstract] > >> As seen in a long thread on the fsdvel scsi mailing lists. Lots of > >> people have headaches and sleep less nights because individual pages > >> can change while in IO and/or DMA. Though each one as slightly different > >> needs, the mechanics look to be the same. > > > Hmm, I don't think it's really about "how to not let pages change" - that > > is doable by using wait_on_page_writeback() in ->page_mkwrite and > > ->write_begin. I think the discussion is more about whether we should do it > > or whether we should rechecksum and resubmit IO in case of checksum failure > > as Nick proposed... > > > > Honza > > I have hijacked the DIF threads but, No, my proposal is for a general > toolset that could be used for all the above as well as DIF if needed. > > Surly even with DIF the keep-constant vs retransmit is a matter of > machine+link speed multiply by faulting work loads. So there might be > situations where an admin wants to choose. > > With other none checksum fixtures, like RAID5/MIRROR this is not always > an option and it becomes keep-constant vs copy. (That is complete > workload copy). So for these setups the option is clear. No? Is it? You can have enough CPU / memory bandwidth to do the copying while you need not be comfortable with a thread blocking until IO is finished when it tries to do a rewrite... > I'm glad that you think it is easy/doable to implement. And I'll surly > test your above receipt. Do you think it would be acceptable as a generic > per-sb tunable. So for instance an ext3 over RAID5 could turn this on > and eliminate the data copy? Yes, that would be useful. At least so that one can get real performance numbers... Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- 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
