On Thu, 7 May 2009 15:16:17 -0700 (PDT) David Rientjes <rientjes@xxxxxxxxxx> wrote: > On Thu, 7 May 2009, Andrew Morton wrote: > > > - 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. > > > > The standard way of controlling the oom killer behavior for a zone is via > the ZONE_OOM_LOCKED bit. oop, I didn't remember/realise that ZONE_OOM_LOCKED already exists. > > - 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. > > > > There's two separate issues here: the use of ZONE_OOM_LOCKED to control > whether or not to invoke the oom killer for a specific zone (which is > already its only function), and the fact that in this case we're doing it > for all zones. It seems like you're concerned with the latter, but the > distinction in the hibernation case is that no memory freeing would be > possible as the result of the oom killer for _all_ zones, so it makes > sense to lock them all out. OK. > > > 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. > > > > I'm not arguing that the only way we can ever implement __GFP_NO_OOM_KILL > is for the entire system: we can set ZONE_OOM_LOCKED for only the zones in > the zonelist that are passed to the page allocator. For this particular > purpose, that is naturally all zones; for other future use cases it may be > chosen only to lock out the zones we're allowed to allocate from in that > context. OK. > > It might well end up that stopping userspace (beforehand or before > > oom-killing) is a hard requirement for reliably disabling the > > oom-killer. > > Yes, globally, but future use cases may disable only specific zones such > as with memory hot-remove. <goes off to find out what ZONE_OOM_LOCKED does> That took remarkably longer than one would have expected.. Yes, OK, I agree, globally setting ZONE_OOM_LOCKED would produce a decent result. The setting and clearing of that thing looks gruesomely racy.. -- 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
