On Thu, 2010-08-19 at 10:37 -0400, Christoph Hellwig wrote: > On Thu, Aug 19, 2010 at 10:15:25AM -0400, Jeff Layton wrote: > > I'm looking at backporting some upstream changes to earlier kernels, > > and ran across something I don't quite understand... > > > > In nfs_commit_unstable_pages, we set the flags to FLUSH_SYNC. We then > > zero out the flags if wbc->nonblocking or wbc->for_background is set. > > > > Shouldn't we also clear it out if wbc->sync_mode == WB_SYNC_NONE ? > > WB_SYNC_NONE means "don't wait on anything", so shouldn't that include > > not waiting on the COMMIT to complete? > > I've been trying to figure out what the nonblocking flag is supposed > to mean for a while now. > > It basically disappeared in commit 0d99519efef15fd0cf84a849492c7b1deee1e4b7 > > "writeback: remove unused nonblocking and congestion checks" > > from Wu. What's left these days is a couple of places in local copies > of write_cache_pages (afs, cifs), and a couple of checks in random > writepages instances (afs, block_write_full_page, ceph, nfs, reiserfs, xfs) > and the use in nfs_write_inode. It's only actually set for memory > migration and pageout, that is VM writeback. > > To me it really doesn't make much sense, but maybe someone has a better > idea what it is for. > > > + if (wbc->nonblocking || wbc->for_background || > > + wbc->sync_mode == WB_SYNC_NONE) > > You could remove the nonblocking and for_background checks as > these impliy WB_SYNC_NONE. To me that sounds fine. I've also been trying to wrap my head around the differences between 'nonblocking', 'for_background', 'for_reclaim' and 'for_kupdate' and how the filesystem is supposed to treat them. Aside from the above, I've used 'for_reclaim', 'for_kupdate' and 'for_background' in order to adjust the RPC request's queuing priority (high in the case of 'for_reclaim' and low for the other two). Cheers Trond -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
