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    SubjectRe: [PATCH v6 0/4] ext4: Coordinate data-only flush requests sent by fsync
    FYI, here's an updated version of my patch to not run pure flushes
    that also works on SCSI/ATA and not just virtio. I suspect the patch
    alone might not be enough, but together with a variant of Neil's
    suggestion might do the trick, with my patch taking care of the
    highend-devices and Neil's scheme of taking care of stupid SATA disks.


    Index: linux-2.6/block/blk-flush.c
    ===================================================================
    --- linux-2.6.orig/block/blk-flush.c 2010-11-30 17:27:33.108254088 +0100
    +++ linux-2.6/block/blk-flush.c 2010-11-30 17:27:38.790004333 +0100
    @@ -143,6 +143,17 @@ struct request *blk_do_flush(struct requ
    unsigned skip = 0;

    /*
    + * Just issue pure flushes directly.
    + */
    + if (!blk_rq_sectors(rq)) {
    + if (!do_preflush) {
    + __blk_end_request_all(rq, 0);
    + return NULL;
    + }
    + return rq;
    + }
    +
    + /*
    * Special case. If there's data but flush is not necessary,
    * the request can be issued directly.
    *
    Index: linux-2.6/drivers/scsi/scsi_lib.c
    ===================================================================
    --- linux-2.6.orig/drivers/scsi/scsi_lib.c 2010-11-30 17:27:33.120254298 +0100
    +++ linux-2.6/drivers/scsi/scsi_lib.c 2010-11-30 17:27:38.791003634 +0100
    @@ -1060,7 +1060,7 @@ int scsi_setup_blk_pc_cmnd(struct scsi_d
    * that does not transfer data, in which case they may optionally
    * submit a request without an attached bio.
    */
    - if (req->bio) {
    + if (req->bio && !(req->cmd_flags & REQ_FLUSH)) {
    int ret;

    BUG_ON(!req->nr_phys_segments);

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