Hello, Peter. On Thu, Dec 03, 2015 at 10:09:11PM +0100, Peter Zijlstra wrote: > On Thu, Dec 03, 2015 at 03:56:32PM -0500, Tejun Heo wrote: > > So, if I'm not mistaken, those are all marking tasks which can be > > depended upon during memory reclaim and we do want to catch them all. > > Up to a point yes, these are things that want to be reliable during > reclaim, but lacking memory reserves and usage bounds (which we > discussed last at lsf/mm) these are just wanna-be.
Hmmm... even if buggy in that they can't guarantee forward-progress even with access to the emergency pool, I think it makes sense to warn them about creating an extra dependency which doesn't have access to the emergency pool. > > PF_MEMALLOC shouldn't depend on something which require memory to be > > reclaimed to guarantee forward progress. > > PF_MEMALLOC basically avoids reclaim for any memory allocation while its > set. So, the assumption is that they're already on the reclaim path and thus shouldn't recurse into it again. > The thing is, even if your workqueue has WQ_MEM_RECLAIM set, it will not > hit the mayday button until you're completely full flat out of memory. It's more trigger-happy than that. It's timer based. If new worker can't be created for a certain amount of time for whatever reason, it'll summon the rescuer. > At which point you're probably boned anyway, because, as per the above, > all that code assumes there's _some_ memory to be had. Not really. PF_MEMALLOC tasks have access to the emergency pool, creating new workers doesn't, so this really is creating a dependency which is qualitatively different. > One solution is to always fail maybe_create_worker() when PF_MEMALLOC is > set, thus always hitting the mayday button. I'm not following. When PF_MEMALLOC is set where? Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
