One of the things that exacerbates write amplification on flash based devices is that fact that data with different lifetimes get grouped together on media. Currently we have no interface that applications can use to separate different types of writes. This patch set adds support for that. The kernel has no knowledge of what stream ID is what. The idea is that writes with identical stream IDs have similar life times, not that stream ID 'X' has a shorter lifetime than stream ID 'X+1'. There are basically two interfaces that could be used for this. One is fcntl, the other is fadvise. This patchset uses fadvise, with a new POSIX_FADV_STREAMID hint. The 'offset' field is used to pass the relevant stream ID. Switching to fcntl (with a SET/GET_STREAMID) would be trivial. The patchset wires up the block parts, adds buffered and O_DIRECT support, and modifies btrfs/xfs too. It should be trivial to extend this to all other file systems, I just used xfs and btrfs for testing. No block drivers are wired up yet. Patches are against current -git. Changes since v1: - Don't add streamid to struct writeback_control, always use the one in the inode for buffered writeback - Add file_streamid() helper. Returns file streamid, if set, otherwise it returns the inode streamid. - Update btrfs/xfs for wbc->streamid change. - Add streamid to ext4. - Bump stream bits from 3 to 8, 255 streams are now supported. -- 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
