On Tue, Feb 21 2012 at 7:31am -0500, Martin K. Petersen <martin.petersen@xxxxxxxxxx> wrote: > >>>>> "Mike" == Mike Snitzer <snitzer@xxxxxxxxxx> writes: > > Mike> This patch fixed the issue for me (though I'm still missing why > Mike> bio->bi_phys_segments was 0 given blkdev_issue_write_same() sets > Mike> it): > > Ok, I see what's going on. You have your own dm-specific make request > function. When cloning the original bio phys_segments isn't carried > over. And that's why we see 0 in sd. Ah, yes indeed. I was just setting out to answer the why on it so you've saved me some time, thanks! > For discard this is not a problem because we hardwire things in sd.c > regardless of what was passed down. And besides you have special > handling for mapping discards in DM. sd allocating the page used for discard was what enabled DM to have discard support; otherwise cloning a discard required allocation of the page and it all got _really_ ugly. > I was trying to avoid perpetuating Christoph's horrible hack (his words, > not mine). But maybe it's better to do it the same way as for discard so > we only have to have to deal with pure evil in one place. Which hack are you referring to? sd allocates the page used for discard (I had a hand in that work, along with tomo, and don't hold it to be too big a hack really). But I'm not immediately seeing a clean way to do so for WRITE SAME because the user provided buffer would need to get down to sd somehow. > I'll contemplate a bit... > > > PS. The good news is that your async stuff works when I set phys_segs to > 1 in sd. Yeah, it worked with the patch I provided in my previous mail too. But ultimately the async stuff wasn't working for me due to merging. -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
