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Date:   Tue, 2 Feb 2021 12:44:20 -0400
From:   Jason Gunthorpe <jgg@ziepe.ca>
To:     Peter Xu <peterx@redhat.com>
Cc:     20200918161902.GX8409@ziepe.ca,
        Linus Torvalds <torvalds@linux-foundation.org>,
        John Hubbard <jhubbard@nvidia.com>,
        Leon Romanovsky <leonro@nvidia.com>,
        Linux-MM <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "Maya B . Gokhale" <gokhale2@llnl.gov>,
        Yang Shi <yang.shi@linux.alibaba.com>,
        Marty Mcfadden <mcfadden8@llnl.gov>,
        Kirill Shutemov <kirill@shutemov.name>,
        Oleg Nesterov <oleg@redhat.com>, Jann Horn <jannh@google.com>,
        Jan Kara <jack@suse.cz>, Kirill Tkhai <ktkhai@virtuozzo.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Christoph Hellwig <hch@lst.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Zhang, Wei" <wzam@amazon.com>
Subject: Re: [PATCH 1/4] mm: Trial do_wp_page() simplification
Message-ID: <20210202164420.GL4718@ziepe.ca>
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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