This patchset adds support for write hints in MD driver. This is a new feature for NVMe drives compliant to 1.3 specification and introduced to Linux in kernel 4.13. Write hint has to be copied from bio containing user data to bios sent to RAID members. Additionally, write hint can be set for internal data like parity and PPL in RAID 5. Setting write hint for parity is done with simple classification algorithm which works for sequential IO workload. It tries to predict which parity request are going to be overwritten in a moment and sets write hint for them. This algorithm uses stripe cache to count updates of each parity chunk. Parity request will be predicted as "soon-overwritten" if nubmer of parity updates is smaller than number of data chunks in stripe. For PPL there is no special algorithm. It is updated very frequently so we can set write hint for each PPL write. We have performed our internal tests which prove that setting write hint for parity and PPL can significantly reduce write amplification. Mariusz Dabrowski (5): raid1: copy write hint from master bio to behind bio raid5: copy write hint from origin bio to stripe raid5: sysfs attribute for write hint policy raid5: set write hint for parity raid5: set write hint for PPL Documentation/admin-guide/md.rst | 16 +++++ drivers/md/raid1.c | 2 + drivers/md/raid5-ppl.c | 4 ++ drivers/md/raid5.c | 147 +++++++++++++++++++++++++++++++++++++-- drivers/md/raid5.h | 10 +++ 5 files changed, 175 insertions(+), 4 deletions(-) -- 2.16.1 -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
