Hi folks, This patchset is the first small step to removing bufferheads from the ->writepage path. The first step to doing this is to simplify the ->writepage path such that we only look up pages once in the radix tree for writeback. This means we only operate on a single page at a time, but a simple conversion loses the mapping efficiency that xfs_cluster_write() gives us. To do this without losing any efficiency we need to retain the active bmbt mapping and ioend chains we build across multiple calls to ->writepage. In general, those multiple sequential page calls come from ->writepages, so we can create a context structure at xfs_vm_writepages() and pass that all the way through to every xfs_vm_writepage() call that occurs from a single writepages context. This allows us to cache the current bmbt mapping as well as keep the ioend chain connected and not have to continually remap the same extent or submit page sized bios and rely on block layer merging to build large IOs. This patch series introduces the struct xfs_writepage_context to act as the holding container for this state, converts the code to use it and removes xfs_cluster_write() as it is no longer needed to efficiently build large IOs. Indeed, the new code is more efficient than the existing code as it does not have arbitrary write clustering limits, and it only does one radix tree lookup per page instead of two. Hence the new code has less CPU overhead, builds larger IOs where appropriate and removes more code than it adds. The last patch of the series (patch 8) is not really a patch - I've included it as information/documentation for the next series of changes that will follow this series that begin one the path of removing bufferheads - mapping pages direct to bios and chaining bios to ioends rather than using bufferheads for this purpose. Once the writepage path is not dependent on bufferheads, we can move to working on the VFS read/write paths that use bufferheads. This will be based on the multipage-write pages that have been floating around for years to - again - map pages directly and operate on them according to the mapping state rather than bufferhead state. This needs to be done to make the COW operations for reflink sane, so that's what is driving this patchset even if it doesn't appear to be connected yet. Comments, flames, thoughts and testing appreciated! -Dave. _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
