On Wed, Aug 22, 2007 at 08:42:01AM -0400, Chris Mason wrote: > > My vague idea is to > > - keep the s_io/s_more_io as a FIFO/cyclic writeback dispatching > > queue. > > - convert s_dirty to some radix-tree/rbtree based data structure. > > It would have dual functions: delayed-writeback and > > clustered-writeback. > > clustered-writeback: > > - Use inode number as clue of locality, hence the key for the sorted > > tree. > > - Drain some more s_dirty inodes into s_io on every kupdate wakeup, > > but do it in the ascending order of inode number instead of > > ->dirtied_when. > > > > delayed-writeback: > > - Make sure that a full scan of the s_dirty tree takes <=30s, i.e. > > dirty_expire_interval. > > I think we should assume a full scan of s_dirty is impossible in the > presence of concurrent writers. We want to be able to pick a start > time (right now) and find all the inodes older than that start time. > New things will come in while we're scanning. But perhaps that's what > you're saying... Yeah, I was thinking about elevators :) Or call it sweeping based on address-hint(inode number). > At any rate, we've got two types of lists now. One keeps track of age > and the other two keep track of what is currently being written. I > would try two things: > > 1) s_dirty stays a list for FIFO. s_io becomes a radix tree that > indexes by inode number (or some arbitrary field the FS can set in the > inode). Radix tree tags are used to indicate which things in s_io are > already in progress or are pending (hand waving because I'm not sure > exactly). > > inodes are pulled off s_dirty and the corresponding slot in s_io is > tagged to indicate IO has started. Any nearby inodes in s_io are also > sent down. > > 2) s_dirty and s_io both become radix trees. s_dirty is indexed by a > sequence number that corresponds to age. It is treated as a big > circular indexed list that can wrap around over time. Radix tree tags > are used both on s_dirty and s_io to flag which inodes are in progress. It's meaningless to convert s_io to radix tree. Because inodes on s_io will normally be sent to block layer elevators at the same time. Also s_dirty holds 30 seconds of inodes, while s_io only 5 seconds. The more inodes, the more chances of good clustering. That's the general rule. s_dirty is the right place to do address-clustering. As for the dirty_expire_interval parameter on dirty age, we can apply a simple rule: do one full scan/sweep over the fs-address-space in every 30s, syncing all inodes encountered, and sparing those newly dirtied in less than 5s. With that rule, any inode will get synced after being dirtied for 5-35 seconds. -fengguang - 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
