On Fri, Dec 18, 2009 at 10:00:21AM +0900, FUJITA Tomonori wrote: > On Fri, 18 Dec 2009 00:57:00 +0100 > James Bottomley <James.Bottomley@xxxxxxx> wrote: > > > On Thu, 2009-12-17 at 20:36 +0100, Jens Axboe wrote: > > > On Thu, Dec 17 2009, Linus Torvalds wrote: > > > > > > > > > > > > On Thu, 17 Dec 2009, tytso@xxxxxxx wrote: > > > > > > > > > > Sure, but there's some rumors/oral traditions going around that some > > > > > block devices want bio address which are page aligned, because they > > > > > want to play some kind of refcounting game, > > > > > > > > Yeah, you might be right at that. > > > > > > > > > And it's Weird Shit(tm) (aka iSCSI, AoE) type drivers, that most of us > > > > > don't have access to, so just because it works Just Fine on SATA doesn't > > > > > mean anything. > > > > > > > > > > And none of this is documented anywhere, which is frustrating as hell. > > > > > Just rumors that "if you do this, AoE/iSCSI will corrupt your file > > > > > systems". > > > > > > > > ACK. Jens? > > > > > > I've heard those rumours too, and I don't even know if they are true. > > > Who has a pointer to such a bug report and/or issue? The block layer > > > itself doesn't not have any such requirements, and the only places where > > > we play page games is for bio's that were explicitly mapped with pages > > > by itself (like mapping user data).o > > > > OK, so what happened is that prior to the map single fix > > > > commit df46b9a44ceb5af2ea2351ce8e28ae7bd840b00f > > Author: Mike Christie <michaelc@xxxxxxxxxxx> > > Date: Mon Jun 20 14:04:44 2005 +0200 > > > > [PATCH] Add blk_rq_map_kern() > > > > > > bio could only accept user space buffers, so we had a special path for > > kernel allocated buffers. That commit unified the path (with a separate > > block API) so we could now submit kmalloc'd buffers via block APIs. > > > > So the rule now is we can accept any user mapped area via > > blk_rq_map_user and any kmalloc'd area via blk_rq_map_kern(). We might > > not be able to do a stack area (depending on how the arch maps the > > stack) and we definitely cannot do a vmalloc'd area. > > > > So it sounds like we only need a blk_rq_map_vmalloc() using the same > > techniques as the patch set and we're good to go. > > I'm not sure about it. > > As I said before (when I was against this 'adding vmalloc support to > the block layer' stuff), are there potential users of this except for > XFS? Are there anyone who does such a thing now? As Christoph already mentioned, XFS is not passing the vmalloc'd range to the block layer - it passes the underlying pages to the block layer. Hence I'm not sure there actually is anyone who is passing vmalloc'd addresses to the block layer. Perhaps we should put a WARN_ON() in the block layer to catch anyone doing such a thing before considering supporting vmalloc'd addresses in the block layer? > This API might be useful for only journaling file systems using log > formats that need large contiguous buffer. Sound like only XFS? FWIW, mapped buffers larger than PAGE_SIZE are used for more than just log recovery in XFS. e.g. filesystems with directory block size larger than page size uses mapped buffers. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-parisc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
