On Fri, May 21, 2010 at 11:21:11AM -0400, Christoph Hellwig wrote: > On Wed, May 19, 2010 at 04:24:51PM -0400, Josef Bacik wrote: > > Btrfs cannot handle having logically non-contiguous requests submitted. For > > example if you have > > > > Logical: [0-4095][HOLE][8192-12287] > > Physical: [0-4095] [4096-8191] > > > > Normally the DIO code would put these into the same BIO's. The problem is we > > need to know exactly what offset is associated with what BIO so we can do our > > checksumming and unlocking properly, so putting them in the same BIO doesn't > > work. So add another check where we submit the current BIO if the physical > > blocks are not contigous OR the logical blocks are not contiguous. > > This gets us slightly less optimal I/O patters for other filesystems in > this case. But it's probably corner case enough to not care and make it > the default. > > But please make the comment in the comment as verbose as the commit > message so that people understand why we're doing this when reading the > code in a few years. > So after I sent this I thought that maybe I could make that test _only_ if we provide submit_bio, that way it only affects btrfs and not everybody else, would you prefer I do something like that? I will make the commit log a bit more verbose. Thanks, Josef -- 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
