James Bottomley wrote: > 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. Hmmm... Right. That means libata either needs to create a separate slab for the sector buf or align it after allocating by itself. Eeeek. Thanks. -- tejun - 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
