On Thu, 7 May 2009 14:25:23 -0700 (PDT) David Rientjes <rientjes@xxxxxxxxxx> wrote: > On Thu, 7 May 2009, Andrew Morton wrote: > > > > > All of your tasks are in D state other than kthreads, right? That means > > > > they won't be in the oom killer (thus no zones are oom locked), so you can > > > > easily do this > > > > > > > > struct zone *z; > > > > for_each_populated_zone(z) > > > > zone_set_flag(z, ZONE_OOM_LOCKED); > > > > > > > > and then > > > > > > > > for_each_populated_zone(z) > > > > zone_clear_flag(z, ZONE_OOM_LOCKED); > > > > > > > > The serialization is done with trylocks so this will never invoke the oom > > > > killer because all zones in the allocator's zonelist will be oom locked. > > > > > > > > Why does this not work for you? > > > > > > Well, it might work too, but why are you insisting? How's it better than > > > __GFP_NO_OOM_KILL, actually? > > > > > > Andrew, what do you think about this? > > > > I don't think I understand the proposal. Is it to provide a means by > > which PM can go in and set a state bit against each and every zone? If > > so, that's still a global boolean, only messier. > > > > Why can't it be global while preallocating memory for hibernation since > nothing but kthreads could allocate at this point and if the system is oom > then the oom killer wouldn't be able to do anything anyway since it can't > kill them? - globals are bad - the standard way of controlling memory allocator behaviour is via the gfp_t. Bypassing that is an unusual step and needs a higher level of justification, which I'm not seeing here. - if we do this via an unusual global, we reduce the chances that another subsytem could use the new feature. I don't know what subsytem that might be, but I bet they're out there. checkpoint-restart, virtual machines, ballooning memory drivers, kexec loading, etc. > The fact is that _all_ allocations here are implicitly __GFP_NO_OOM_KILL > whether it specifies it or not since the oom killer would simply kill a > task in D state which can't exit or free memory and subsequent allocations > would make the oom killer a no-op because there's an eligible task with > TIF_MEMDIE set. The only thing you're saving with __GFP_NO_OOM_KILL is > calling the oom killer in a first place and killing an unresponsive task > but that would have to happen anyway when thawed since the system is oom > (or otherwise lockup for GFP_KERNEL with order < PAGE_ALLOC_COSTLY_ORDER). All the above is specific to the PM application only, when userspace tasks are stopped. It might well end up that stopping userspace (beforehand or before oom-killing) is a hard requirement for reliably disabling the oom-killer. Because the __GFP_NO_OOM_KILL user will be safe, but random other allocations from other tasks will not be. So perhaps we _do_ need a global, and random userspace processes should test and sleep upon that global if they're heading in the direction of the oom-killer. -- To unsubscribe from this list: send the line "unsubscribe kernel-testers" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
