linux-kernel - Re: [PATCH 1/4] mm: Trial do_wp

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Date:   Tue, 2 Feb 2021 12:44:20 -0400
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Peter Xu <peterx@...hat.com>
Cc:     20200918161902.GX8409@...pe.ca,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        John Hubbard <jhubbard@...dia.com>,
        Leon Romanovsky <leonro@...dia.com>,
        Linux-MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Maya B . Gokhale" <gokhale2@...l.gov>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        Marty Mcfadden <mcfadden8@...l.gov>,
        Kirill Shutemov <kirill@...temov.name>,
        Oleg Nesterov <oleg@...hat.com>, Jann Horn <jannh@...gle.com>,
        Jan Kara <jack@...e.cz>, Kirill Tkhai <ktkhai@...tuozzo.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Christoph Hellwig <hch@....de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Zhang, Wei" <wzam@...zon.com>
Subject: Re: [PATCH 1/4] mm: Trial do_wp_page() simplification

On Tue, Feb 02, 2021 at 11:31:27AM -0500, Peter Xu wrote:
> On Tue, Feb 02, 2021 at 04:40:33PM +0200, Gal Pressman wrote:
> > Hi Peter & Jason,
> 
> Hi, Gal, Jason,
> 
> > 
> > It seems the hugetlb part was overlooked?
> > We're testing if the RDMA fork MADV_DONTFORK stuff can be removed on appropriate
> > kernels, but our tests still fail due to lacking explicit huge pages support [1].
> 
> I didn't think it high priority only because I think most hugetlbfs users
> should be using it shared, but maybe I'm wrong..  Then it got lost indeed.

It turns out people are doing this:

mmap(NULL, SEND_BUFF_SIZE, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB, -1, 0)

Which makes some sense...

Gal, you could also MADV_DONTFORK this range if you are explicitly
allocating them via special mmap.

Jason