On Thu, Jul 03, 2014 at 03:39:11PM +1000, Dave Chinner wrote: > There's another regression with the optimisitic spinning in rwsems > as well: it increases the size of the struct rw_semaphore by 16 > bytes. That has increased the size of the struct xfs_inode by 32 > bytes. > > That's pretty damn significant - it's no uncommon to see machines > with tens of millions of cached XFS inodes, so increasing the size > of the inode by 4% is actually very significant. That's enough to go > from having a well balanced workload to not being able to fit the > working set of inodes in memory. > > Filesystem developers will do almost anything to remove a few bytes > from the struct inode because inode cache footprint is extremely > important for performance. We also tend to get upset and > unreasonable when other people undo that hard work by making changes > that bloat the generic structures embedded in the inode > structures....
Jason Low actually did a patch, yesterday, to shrink rwsem back to its old size (on 64bit).
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