Messages in this thread | | | Date | Thu, 15 Dec 2005 17:26:01 +0100 | From | Pavel Machek <> | Subject | Re: [RFC][PATCH 0/6] Critical Page Pool |
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Hi!
> > I don't see how this can ever work. > > > > How can _userspace_ know about what allocations are critical to the > > kernel?! > > Well, it isn't userspace that is determining *which* allocations are > critical to the kernel. That is statically determined at compile time by > using the flag __GFP_CRITICAL on specific *kernel* allocations. Sridhar, > cc'd on this mail, has a set of patches that sprinkle the __GFP_CRITICAL > flag throughout the networking code to take advantage of this pool. > Userspace is in charge of determining *when* we're in an emergency > situation, and should thus use the critical pool, but not *which*
It still is not too reliable. If you userspace tool is swapped out (etc), it may not get chance to wake up.
> > And as you noticed, it does not work for your original usage case, > > because reserved memory pool would have to be "sum of all network > > interface bandwidths * ammount of time expected to survive without > > network" which is way too much. > > Well, I never suggested it didn't work for my original usage case. The > discussion we had is that it would be incredibly difficult to 100% > iron-clad guarantee that the pool would NEVER run out of pages. But we can > size the pool, especially given a decent workload approximation, so as to > make failure far less likely.
Perhaps you should add file in Documentation/ explaining it is not reliable?
> > If you want few emergency pages for some strange hack you are doing > > (swapping over network?), just put swap into ramdisk and swapon() it > > when you are in emergency, or use memory hotplug and plug few more > > gigabytes into your machine. But don't go introducing infrastructure > > that _can't_ be used right. > > Well, that's basically the point of posting these patches as an RFC. I'm > not quite so delusional as to think they're going to get picked up right > now. I was, however, hoping for feedback to figure out how to design > infrastructure that *can* be used right, as well as trying to find other > potential users of such a feature.
Well, we don't usually take infrastructure that has no in-kernel users, and example user would indeed be nice. Pavel -- Thanks, Sharp! - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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