On 13:57 07/07, Matthew Wilcox wrote: > On Tue, Jul 07, 2020 at 07:43:46AM -0500, Goldwyn Rodrigues wrote: > > On 9:53 01/07, Christoph Hellwig wrote: > > > On Mon, Jun 29, 2020 at 02:23:49PM -0500, Goldwyn Rodrigues wrote: > > > > From: Goldwyn Rodrigues <rgold...@suse.com> > > > > > > > > For direct I/O, add the flag IOMAP_DIO_RWF_NO_STALE_PAGECACHE to > > > > indicate > > > > that if the page invalidation fails, return back control to the > > > > filesystem so it may fallback to buffered mode. > > > > > > > > Reviewed-by: Darrick J. Wong <darrick.w...@oracle.com> > > > > Signed-off-by: Goldwyn Rodrigues <rgold...@suse.com> > > > > > > I'd like to start a discussion of this shouldn't really be the > > > default behavior. If we have page cache that can't be invalidated it > > > actually makes a whole lot of sense to not do direct I/O, avoid the > > > warnings, etc. > > > > > > Adding all the relevant lists. > > > > Since no one responded so far, let me see if I can stir the cauldron :) > > > > What error should be returned in case of such an error? I think the > > Christoph's message is ambiguous. I don't know if he means "fail the > I/O with an error" or "satisfy the I/O through the page cache". I'm > strongly in favour of the latter. Indeed, I'm in favour of not invalidating > the page cache at all for direct I/O. For reads, I think the page cache > should be used to satisfy any portion of the read which is currently
That indeed would make reads faster. How about if the pages are dirty during DIO reads? Should a direct I/O read be responsible for making sure that the dirty pages are written back. Technically direct I/O reads is that we are reading from the device. > cached. For writes, I think we should write into the page cache pages > which currently exist, and then force those pages to be written back, > but left in cache. Yes, that makes sense. If this is implemented, what would be the difference between O_DIRECT and O_DSYNC, if any? -- Goldwyn
