On Mon, Dec 15, 2014 at 07:49:20AM -0500, Trond Myklebust wrote: > On Mon, Dec 15, 2014 at 12:26 AM, Omar Sandoval <osandov@xxxxxxxxxxx> wrote: > > The generic callers of direct_IO lock i_mutex before doing a write. NFS > > doesn't use the generic write code, so it doesn't follow this > > convention. This is now a problem because the interface introduced for > > swap-over-NFS calls direct_IO for a write without holding i_mutex, but > > other implementations of direct_IO will expect to have it locked. > > I really don't care much about swap-over-NFS performance; that's a > niche usage at best. I _do_ care about O_DIRECT performance, and the > ability to run multiple WRITE calls in parallel. > > IOW: Patch NACKed... Please find another solution. > > Trond So the patch formatting doesn't make it completely clear what's going on here, but here's what the original nfs_file_direct_write code did: - called with i_mutex unlocked - collects stats and does some generic checks - locks i_mutex - syncs the mapping, schedules the write - unlocks i_mutex - waits for the write to complete if synchronous After this patch, nfs_file_direct_write works like: - called with i_mutex locked - collects stats and does some generic checks - syncs the mapping, schedules the write - drops i_mutex - waits for the write to complete if synchronous - picks i_mutex back up There's an extra lock and unlock as a result and a slightly longer critical section, but we drop i_mutex to wait for the write, so multiple writes still work in parallel. -- Omar -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
