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Date: Thu, 27 Feb 2014 13:27:15 -0800 From: Kent Overstreet <kmo@...erainc.com> To: Matthew Wilcox <willy@...ux.intel.com> Cc: axboe@...nel.dk, linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org, Neil Brown <neilb@...e.de>, Alasdair Kergon <agk@...hat.com>, dm-devel@...hat.com, Lars Ellenberg <drbd-dev@...ts.linbit.com>, drbd-user@...ts.linbit.com, Asai Thambi S P <asamymuthupa@...ron.com>, Sam Bradshaw <sbradshaw@...ron.com>, linux-nvme@...ts.infradead.org, Jiri Kosina <jkosina@...e.cz>, Geoff Levand <geoff@...radead.org>, Jim Paris <jim@...n.com>, Joshua Morris <josh.h.morris@...ibm.com>, Philip Kelleher <pjk1939@...ux.vnet.ibm.com>, Minchan Kim <minchan@...nel.org>, Nitin Gupta <ngupta@...are.org>, Martin Schwidefsky <schwidefsky@...ibm.com>, Heiko Carstens <heiko.carstens@...ibm.com>, Peng Tao <bergwolf@...il.com> Subject: Re: [PATCH 1/9] block: Make generic_make_request handle arbitrary sized bios On Thu, Feb 27, 2014 at 12:22:54PM -0500, Matthew Wilcox wrote: > On Wed, Feb 26, 2014 at 03:39:49PM -0800, Kent Overstreet wrote: > > We do this by adding calls to blk_queue_split() to the various > > make_request functions that need it - a few can already handle arbitrary > > size bios. Note that we add the call _after_ any call to blk_queue_bounce(); > > this means that blk_queue_split() and blk_recalc_rq_segments() don't need to > > be concerned with bouncing affecting segment merging. > > > diff --git a/drivers/block/nvme-core.c b/drivers/block/nvme-core.c > > index 51824d1f23..e4376b9613 100644 > > --- a/drivers/block/nvme-core.c > > +++ b/drivers/block/nvme-core.c > > @@ -737,6 +737,8 @@ static void nvme_make_request(struct request_queue *q, struct bio *bio) > > struct nvme_queue *nvmeq = get_nvmeq(ns->dev); > > int result = -EBUSY; > > > > + blk_queue_split(q, &bio, q->bio_split); > > + > > if (!nvmeq) { > > put_nvmeq(NULL); > > bio_endio(bio, -EIO); > > I'd suggest that we do: > > - struct nvme_queue *nvmeq = get_nvmeq(ns->dev); > + struct nvme_queue *nvmeq; > int result = -EBUSY; > > + blk_queue_split(q, &bio, q->bio_split); > + > + nvmeq = get_nvmeq(ns->dev); > if (!nvmeq) { > > so that we're running the blk_queue_split() code outside the get_cpu() > call. Whoops, that's definitely a bug. > Now, the NVMe driver has its own rules about when BIOs have to be split. > Right now, that's way down inside the nvme_map_bio() call when we're > walking the bio to compose the scatterlist. Should we instead have an > nvme_bio_split() routine that is called instead of blk_queue_split(), > and we can simplify nvme_map_bio() since it'll know that it's working > with bios that don't have to be split. > > In fact, I think it would have little NVMe-specific in it at that point, > so we could name __blk_bios_map_sg() better, export it to drivers and > call it from nvme_map_bio(), which I think would make everybody happier. Yes, definitely - and by doing it there we shoudn't even have to split the bios, we can just process them incrementally. I can write a patch for it later if you want to test it. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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