From mboxrd@z Thu Jan  1 00:00:00 1970
From: Matthew Wilcox <willy@infradead.org>
Subject: Re: [RFC 1/2] Protect larger order pages from breaking up
Date: Fri, 16 Feb 2018 13:43:53 -0800
Message-ID: <20180216214353.GA32655@bombadil.infradead.org>
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To: Dave Hansen <dave.hansen@intel.com>
Cc: Christopher Lameter <cl@linux.com>, Mel Gorman <mel@skynet.ie>, linux-mm@kvack.org, linux-rdma@vger.kernel.org, akpm@linux-foundation.org, Thomas Schoebel-Theuer <tst@schoebel-theuer.de>, andi@firstfloor.org, Rik van Riel <riel@redhat.com>, Michal Hocko <mhocko@kernel.org>, Guy Shattah <sguy@mellanox.com>, Anshuman Khandual <khandual@linux.vnet.ibm.com>, Michal Nazarewicz <mina86@mina86.com>, Vlastimil Babka <vbabka@suse.cz>, David Nellans <dnellans@nvidia.com>, Laura Abbott <labbott@redhat.com>, Pavel Machek <pavel@ucw.cz>, Mike Kravetz <mike.kravetz@oracle.com>
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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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