Hi, Considering the current interfaces of F2FS and EXT4, my thought is that we can define a generic user-modifiable flag FS_DAX_FL, which can be included in the i_flags field of [f2fs | ext4]_inode_info. Thus, DAX can be enabled in either of the two ways below: 1) mount the FS with a "dax" option, so that all files created will have the flag S_DAX set in the VFS inode, and the flag FS_DAX_FL set in [f2fs | ext4]_inode_info, by default. 2) mount the FS without "dax", and enable DAX per-inode from f2fs_ioctl_setflags() => f2fs_set_inode_flags() Thanks, ________________________________________ From: Jaegeuk Kim [jaegeuk@xxxxxxxxxx] Sent: Wednesday, July 26, 2017 10:16 To: Dan Williams Cc: sunqiuyang; Linux Kernel Mailing List; linux-fsdevel; linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx; linux-nvdimm@xxxxxxxxxxxx Subject: Re: [PATCH v8 1/1] f2fs: dax: implement direct access Hi Dan, On 07/25, Dan Williams wrote: > [ adding linux-nvdimm ] > > On Thu, Jul 20, 2017 at 5:10 AM, sunqiuyang <sunqiuyang@xxxxxxxxxx> wrote: > > From: Qiuyang Sun <sunqiuyang@xxxxxxxxxx> > > > > This patch implements Direct Access (DAX) in F2FS, including: > > - a mount option to choose whether to enable DAX or not > > We're in the process of walking back and potentially deprecating the > use of the dax mount option for xfs and ext4 since dax can have > negative performance implications if page cache memory happens to be > faster than pmem. It should be limited to applications that > specifically want the semantic, not globally enabled for the entire > mount. xfs has went ahead and added the XFS_DIFLAG2_DAX indoe flag for > per-inode enabling of dax. Thank you so much for pointing this out. So, is there a plan to define a generic inode flag to enable dax via inode_set_flag? Or, does each filesystem need to handle it individually likewise xfs? > > I'm wondering if any new filesystem that adds dax support at this > point should do so with inode flags and not a mount option? Anyway, in such the case, I have to postpone merging this patch for a while. Thanks,
