On Mon, 14 Mar 2011 17:11:19 -0400 "Ted Ts'o" <tytso@xxxxxxx> wrote: > On Mon, Mar 14, 2011 at 01:10:42PM -0700, Andrew Morton wrote: > > > > There might one day be a requirement to be able to initiate a > > resource-management-style writeback against a whole filesystem. When > > that happens, we'll regret not having added a "mode" argument to > > sys_syncfs(). > > I'm a bit nervous about exposing WB_SYNC_NONE to userspace, because > its semantics are *definitely* hard to describe. For example, at the > moment if you do a WB_SYNC_NONE writeback, the writeback code will > clamp the amount of data written back for each inode to > MAX_WRITEBACK_PAGES (1024) pages. Wha? It does? When did that get broken? > Do we want to document that? > Probably not! But if we don't document it, what can userspace expect? > > If you just issue a writeback_inodes_sb(), it's not the case that it > will start a process that will eventually write out everything (i.e., > it's not the equivalent of a non-blocking data integrity sync). It > just means, "write out some stuff". > > I could imagine userspace wanting to start a non-blocking writeout of > all data blocking pages, and which doesn't cause queue flush / barrier > requests. (i.e., a non-blocking-non-barrier-issuing-but-otherwise-a- > data-integrity writeback) But that's not something that the current > writeback machinery can do easily, at least not today. Well. Current implementation shortcomings don't carry a lot of weight when designing a permanent interface. > It wouldn't hurt to have a "flags" field which we could expand later > --- but that can lead to portability headaches for userspace programs > that don't know whether a particular kernel is going to support a > particular flag or not. So it's certainly not a panacea. I don't see a need to add an arg to syncfs() really. But we should demonstrate that we've thought about it ;) -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
