linux-kernel - Re: Plumbers 2018 - Performance and Scalability Microconference

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Message-Id: <4d6a466c-6f77-b54e-fb30-9ad8e5bb4023@linux.vnet.ibm.com>
Date:   Thu, 6 Sep 2018 09:45:05 +0200
From:   Laurent Dufour <ldufour@...ux.vnet.ibm.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Christopher Lameter <cl@...ux.com>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        linux-kernel@...r.kernel.org,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Aaron Lu <aaron.lu@...el.com>, alex.kogan@...cle.com,
        akpm@...ux-foundation.org, boqun.feng@...il.com, brouer@...hat.com,
        dave@...olabs.net, dave.dice@...cle.com,
        Dhaval Giani <dhaval.giani@...cle.com>, ktkhai@...tuozzo.com,
        Pavel.Tatashin@...rosoft.com, paulmck@...ux.vnet.ibm.com,
        shady.issa@...cle.com, tariqt@...lanox.com, tim.c.chen@...el.com,
        vbabka@...e.cz, longman@...hat.com, yang.shi@...ux.alibaba.com,
        shy828301@...il.com, Huang Ying <ying.huang@...el.com>,
        subhra.mazumdar@...cle.com,
        Steven Sistare <steven.sistare@...cle.com>, jwadams@...gle.com,
        ashwinch@...gle.com, sqazi@...gle.com,
        Shakeel Butt <shakeelb@...gle.com>, walken@...gle.com,
        rientjes@...gle.com, junaids@...gle.com,
        Neha Agarwal <nehaagarwal@...gle.com>
Subject: Re: Plumbers 2018 - Performance and Scalability Microconference

On 06/09/2018 01:01, Thomas Gleixner wrote:
> On Wed, 5 Sep 2018, Laurent Dufour wrote:
>> On 05/09/2018 17:10, Christopher Lameter wrote:
>>> Large page sizes also reduce contention there.
>>
>> That's true for the page fault path, but for process's actions manipulating the
>> memory process's layout (mmap,munmap,madvise,mprotect) the impact is minimal
>> unless the code has to manipulate the page tables.
> 
> And how exactly are you going to do any of those operations _without_
> manipulating the page tables?

I agree, at one time the page tables would have to be manipulated, and this is
mostly done under the protection of the page table locks - should the mmap_sem
still being held then ?

I was thinking about all the processing done on the VMAs, accounting, etc.
That part, usually not manipulating the page tables, is less dependent of the
underlying page size.

But I agree at one time of the processing, the page table are manipulated and
dealing with larger pages is better then.

Thanks,
Laurent.