On Mon, Feb 22, 2016 at 12:58:18PM -0500, Jeff Moyer wrote: > Sorry for being dense, but why, exactly? If the file system is making > changes without the application's involvement, then the file system > should be responsible for ensuring its own consistency, irrespective of > whether the application issues an fsync. Clearly I'm missing some key > point here. The simplest example is a copy on write file system (or simply a copy on write file, which can exist with ocfs2 and will with xfs very soon), where each write will allocate a new block, which will require metadata updates. We've built the whole I/O model around the concept that by default our I/O will required fsync/msync. For read/write-style I/O you can opt out using O_DSYNC. There currently is no way to opt out for memory mapped I/O, mostly because it's a) useless without something like DAX, and b) much harder to implement So a MAP_SYNC option might not be entirely off the table, but I think it would be a lot of hard work and I'm not even sure it's possible to handle it in the general case. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>