Re: [RFC 1/2] Protect larger order pages from breaking up

[Matthew Wilcox <willy@infradead.org>]

On Fri, Feb 16, 2018 at 01:08:11PM -0800, Dave Hansen wrote:
> On 02/16/2018 12:15 PM, Christopher Lameter wrote:
> >> This has the potential to be really confusing to apps.  If this memory
> >> is now not available to normal apps, they might plow into the invisible
> >> memory limits and get into nasty reclaim scenarios.
> >> Shouldn't this subtract the memory for MemFree and friends?
> > Ok certainly we could do that. But on the other hand the memory is
> > available if those subsystems ask for the right order. Its not clear to me
> > what the right way of handling this is. Right now it adds the reserved
> > pages to the watermarks. But then under some circumstances the memory is
> > available. What is the best solution here?
> 
> There's definitely no perfect solution.
> 
> But, in general, I think we should cater to the dumbest users.  Folks
> doing higher-order allocations are not that.  I say we make the picture
> the most clear for the traditional 4k users.

Your way might be confusing -- if there's a system which is under varying
amounts of jumboframe load and all the 16k pages get gobbled up by the
ethernet driver, MemFree won't change at all, for example.

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