On Tue, 2009-09-01 at 13:19 +0200, Jens Axboe wrote: > Originally, MAX_WRITEBACK_PAGES was hard-coded to 1024 because of a > concern of not holding I_SYNC for too long. (At least, that was the > comment previously.) This doesn't make sense now because the only > time we wait for I_SYNC is if we are calling sync or fsync, and in > that case we need to write out all of the data anyway. Previously > there may have been other code paths that waited on I_SYNC, but not > any more. > > According to Christoph, the current writeback size is way too small, > and XFS had a hack that bumped out nr_to_write to four times the value > sent by the VM to be able to saturate medium-sized RAID arrays. This > value was also problematic for ext4 as well, as it caused large files > to be come interleaved on disk by in 8 megabyte chunks (we bumped up > the nr_to_write by a factor of two). > > So, in this patch, we make the MAX_WRITEBACK_PAGES a tunable, and > change the default to be 32768 blocks. Do we really need a tunable for this? I guess we need a limit to avoid it writing out everything, but can't we have something automagic? -- 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
