On Fri, Aug 20, 2010 at 07:27:57AM -0400, Jeff Layton wrote: > On Fri, 20 Aug 2010 05:19:04 -0400 > Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > > > On Fri, Aug 20, 2010 at 07:55:53AM +0800, Wu Fengguang wrote: > > > Since migration and pageout still set nonblocking for ->writepage, we > > > may keep them in the near future, until VM does not start IO on itself. > > > > Why does pageout() and memory migration need to be even more > > non-blocking than the already non-blockig WB_SYNC_NONE writeout? > > > > Just an idle thought on this... > > I think a lot of the confusion here comes from the fact that we have > sync_mode and a bunch of flags, and it's not at all clear how > filesystems are supposed to treat the union of them. There are also > possible unions of flags/sync_modes that never happen in practice. It's > not always obvious though and as filesystem implementors we have to > consider the possibility that they might occur (consider WB_SYNC_ALL + > for_background). > > Perhaps a lot of this confusion could be lifted by getting rid of the > extra flags and adding new sync_mode's. Maybe something like: > > WB_SYNC_ALL /* wait on everything to complete */ > WB_SYNC_NONE /* don't wait on anything */ > WB_SYNC_FOR_RECLAIM /* sync for reclaim */ > WB_SYNC_FOR_KUPDATED /* sync by kupdate */ > ...etc... > > That does mean that all of the filesystem specific code may need to be > touched when new modes are added and removed. I think it would be > clearer though about what you're supposed to do in ->writepages. No, we are moving towards the other direction :) I just removed the definition of wbc->nonblocking and wbc->encountered_congestion and all of the references. Sorry for the confusion! Thanks, Fengguang -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>