On 28/02/13 11:58, Jan Beulich wrote: >>>> On 28.02.13 at 11:28, Roger Pau Monne <roger....@citrix.com> wrote: >> dev_bus_addr returned in the grant ref map operation is the mfn of the >> passed page, there's no need to store it in the persistent grant >> entry, since we can always get it provided that we have the page. > > Interesting that you come up with this, as I have a similar patch > pending (not posted yet), aiming at reducing the stack usage in > dispatch_rw_block_io(): seg[].buf is really unnecessary with the > dev_bus_addr storing removed, as the only reader of that field > can equally well use req->u.rw.seg[i].first_sect.
Well, it can if we are not using indirect descriptors, because once we start using indirect descriptors segments are inside a gref frame, so it's quite comfortable to store first_sect inside a separate array, this way we can map indirect segments, copy whatever data we need from them and unmap them, without having them around for the whole lifetime of the request. > > And then the biolist[] array really can be folded into a union > with the remaining seg[] one, as their usage scopes are easily > separable. Could we leave that for a further patch? I would like to avoid messing any more with blkback, as I'm already touching a lot of bits with this patch series. > >> --- a/drivers/block/xen-blkback/blkback.c >> +++ b/drivers/block/xen-blkback/blkback.c >> @@ -621,9 +621,7 @@ static int xen_blkbk_map(struct blkif_request *req, >> * If this is a new persistent grant >> * save the handler >> */ >> - persistent_gnts[i]->handle = map[j].handle; >> - persistent_gnts[i]->dev_bus_addr = >> - map[j++].dev_bus_addr; >> + persistent_gnts[i]->handle = map[j++].handle; >> } >> pending_handle(pending_req, i) = >> persistent_gnts[i]->handle; >> @@ -631,7 +629,8 @@ static int xen_blkbk_map(struct blkif_request *req, >> if (ret) >> continue; >> >> - seg[i].buf = persistent_gnts[i]->dev_bus_addr | >> + seg[i].buf = pfn_to_mfn(page_to_pfn( >> + persistent_gnts[i]->page)) << PAGE_SHIFT | > > So why do you do this? The only reader masks the field with > ~PAGE_MASK anyway. Yes, I only need to store first_sect. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
