On Wed, May 18, 2022 at 9:47 PM Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > > On Sat, May 07, 2022 at 12:10:33PM +0800, Liang Chen wrote: > > From: Liang Chen <liangchen.linux@xxxxxxxxx> > > > > As pointed out in commit 332391a, mixing buffered reads and asynchronous > > direct writes risks ending up with a situation where stale data is left > > in page cache while new data is already written to disk. The same problem > > hits block dev fs too. A similar approach needs to be taken here. > > What is the real issue here? If you mix direct and buffered I/O > you generally get what you pay for. Even more so on block devices that > don't even follow Posix file system semantics. Sorry, missed your reply. You are right. The problem was manifested when mixing direct and buffered I/O, and can be avoided by not doing so. I tried to bring block device direct IO onto one of the generic DIO paths, but it resulted in some noticeable performance degradation. So I would rather leave it as is, since as you mentioned block devices don't even follow Posix file system semantics. Thanks, Liang
