linux-kernel - Re: [RFC] mmap(MAP

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Message-ID: <434a5870-0115-b8ab-bd6c-b7f4db847dc4@oracle.com>
Date:   Wed, 4 Oct 2017 10:38:57 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Christopher Lameter <cl@...ux.com>,
        Anshuman Khandual <khandual@...ux.vnet.ibm.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-api@...r.kernel.org,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Michal Nazarewicz <mina86@...a86.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Guy Shattah <sguy@...lanox.com>
Subject: Re: [RFC] mmap(MAP_CONTIG)

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