On Fri 04-06-10 12:30:09, J. Bruce Fields wrote: > On Fri, Jun 04, 2010 at 06:23:32PM +0200, 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. > > Will the same work for the NFS server checksumming page data in read > replies? Currently it won't. The above relies on the fact that when we clear dirty page flag in clear_page_dirty_for_io we also write-protect the page. Moreover I suppose you don't set PageWriteback when serving a content from a page... But an elegant way to solve this would IMHO be to do: lock_page(page); if (page_mkclean(page)) set_page_dirty(page); and now you can be sure that until you unlock the page it cannot be modified because both ->page_mkwrite and ->write_begin need page lock before they can go and modify a page... 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
