On 05/03/2009 06:42 PM, Matthew Wilcox wrote: > On Sun, May 03, 2009 at 06:02:51PM +0300, Boaz Harrosh wrote: >> I agree with Hugh. The allocation is done at, too-low in the food chain. >> (And that free of buffer at upper layer allocated by lower layer). >> >> I think you need to separate the: "does lld need buffer, what size" >> from the "here is buffer prepare", so upper layer that can sleep does >> sleep. > > So you want two function pointers in the request queue relating to discard? > OK I don't know what I want, I guess. ;-) I'm not a block-device export but from the small osdblk device I maintain it looks like osdblk_prepare_flush which is set into: blk_queue_ordered(q, QUEUE_ORDERED_DRAIN_FLUSH, osdblk_prepare_flush); does some internal structure setup, but the actual flush command is only executed later in the global osdblk_rq_fn which is set into: blk_init_queue(osdblk_rq_fn, &osdev->lock); But I'm not even sure that prepare_flush is called in a better context then queue_fn, and what does it means to let block devices take care of another new command type at queue_fn. I guess it comes back to Jeff Garzik's comment about not having a central place to ask the request what we need to do. But I do hate that allocation is done by driver and free by mid-layer, so yes two vectors, request_queue is allocated once per device it's not that bad. And later when Jeff's comment is addressed it can be removed. >> In all other buffer needing operations the allocation is done before >> submission of request, No? > > It's not true for the flush request (the example I quoted). Obviously, > the solution adopted here by IDE is Bad and Wrong ... > So now I don't understand, is flush executed by the queue_fn or by the prepare_flush, or am I seeing two type of flushes? Thanks Boaz -- 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