linux-kernel - Re: [RFC PATCH 00/16] 1GB THP support on x86

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Date:   Wed, 9 Sep 2020 10:14:49 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Zi Yan <ziy@...dia.com>, David Hildenbrand <david@...hat.com>,
        Roman Gushchin <guro@...com>,
        "Kirill A. Shutemov" <kirill@...temov.name>, linux-mm@...ck.org,
        Rik van Riel <riel@...riel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        David Nellans <dnellans@...dia.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 00/16] 1GB THP support on x86_64

On Wed, Sep 09, 2020 at 01:32:44PM +0100, Matthew Wilcox wrote:

> But here's the thing ... we already allow
> 	mmap(MAP_POPULATE | MAP_HUGETLB | MAP_HUGE_1GB)
> 
> So if we're not doing THP, what's the point of this thread?

I wondered that too..

> An madvise flag is a different beast; that's just letting the kernel
> know what the app thinks its behaviour will be.  The kernel can pay

But madvise is too late, the VMA already has an address, if it is not
1G aligned it cannot be 1G THP already.

Jason