On 10/28/2013 10:57 AM, Shaohua Li wrote: > > > > 2013/10/28 Jens Axboe <ax...@kernel.dk <mailto:ax...@kernel.dk>> > > On 10/28/2013 02:48 AM, Christoph Hellwig wrote: > > On Sun, Oct 27, 2013 at 10:29:25PM +0000, Jens Axboe wrote: > >> On Sat, Oct 26 2013, Christoph Hellwig wrote: > >>> I think this variant of the patch from Alexander should fix the > issue > >>> in a minimally invasive way. Longer term I'd prefer to use > q->flush_rq > >>> like in the non-mq case by copying over the context and tag > information. > >> > >> This one is pretty simple, we could definitely use it as a band > aid. I > >> too would greatly prefer using the static ->flush_rq instead. > Just have > >> it marked to bypass most of the free logic. > > > > We already bypass the free logical by setting and end_io callback for > > a while, similar to what the old code does. Maybe it's not all that > > hard to prealloc the request, let me give a sping. Using the static > > allocated one will be hard due to the driver-specific extra data, > > though. > > It's not that I think the existing patch is THAT bad, it fits in alright > with the reserved tagging and works regardless of whether a driver uses > reserved tags or not. And it does have the upside of not requiring > special checks or logic for this special non-tagged request that using > the preallocated would might need. > > >> I'll add this one. > > > > Gimme another day or so to figure this out. > > OK, holding off. > > > Another option: we could throttle flush-request allocation in > blk_mq_alloc_request(), for example, flush_req_nr >= max_tags - 1, make > the allocation wait.
That could work too. If we back off, then we could restart it once a request completes. That does, however, requiring checking that and potentially kicking all the queues on completion when that happens. -- Jens Axboe -- 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/
