On Fri, 2008-02-15 at 07:49 +0900, Tejun Heo wrote: > James Bottomley wrote: > > On Thu, 2008-02-14 at 18:48 +0900, Tejun Heo wrote: > >> shost->hostdata can contain arbitrary data including DMA target > >> buffers. Align it to cacheline. > >> > >> Signed-off-by: Tejun Heo <htejun@xxxxxxxxx> > >> --- > >> James, what do you think? > > > > Hmm, it will blow out the host size ... although that's not such a huge > > problem since there are relatively few of them in most running kernels. > > What's the actual use case for this, though? The host structure is > > allocated in ordinary memory ... we don't make sure it's DMAable, and > > most HBAs that want to use memory for mailboxes need coherent memory > > anyway. > > "As it can contain arbitrary structure, it should follow the largest > meaningful alignment to allow the contained structure proper alignment." > is the logic. I think it's generally RTTD for inline private data but > feel free to disagree. Well, the way we usually do that is to have the host float the alignment if necessary. The problem with relying on __cacheline_aligned for an allocated structure is that it only works if the allocated structure actually begins on a cacheline. Kmalloc (which is where we get the host from) doesn't necessarily obey this if certain slab debugging flags are present. James - To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
