Re: [RFC] mmap(MAP_CONTIG)

From: Mike Kravetz
Date: Wed Oct 04 2017 - 13:39:20 EST

On 10/04/2017 09:05 AM, Christopher Lameter wrote:
> On Wed, 4 Oct 2017, Anshuman Khandual wrote:
>>> - Using 'pre-allocated' pages in the fault paths may be intrusive.
>> But we have already faulted in all of them for the mapping and they
>> are also locked. Hence there should not be any page faults any more
>> for the VMA. Am I missing something here ?
> The PTEs may be torn down and have to reestablished through a page faults.
> Page faults would not allocate memory.
>> I am still wondering why wait till fault time not pre fault all of them
>> and populate the page tables.
> They are populated but some processes (swap and migration) may tear them
> down.

As mentioned in my reply to Anshuman, the mention of fault paths here
may be a source of confusion. I would expect the entire mapping to be
populated at mmap time, and the pages locked. Therefore, there should
be no swap or migration.

Mike Kravetz