linux-kernel - Re: [PATCHv5 2/3] mm/gup: fix omission of check on FOLL

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Message-ID: <CAFgQCTuK5nTrm_ijohhCJyvUmiVXueGrxbqqM381ViZyx0_MxA@mail.gmail.com>
Date:   Mon, 2 Mar 2020 10:28:45 +0800
From:   Pingfan Liu <kernelfans@...il.com>
To:     Ira Weiny <ira.weiny@...el.com>
Cc:     Linux-MM <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Matthew Wilcox <willy@...radead.org>,
        John Hubbard <jhubbard@...dia.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Christoph Hellwig <hch@...radead.org>,
        Shuah Khan <shuah@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv5 2/3] mm/gup: fix omission of check on FOLL_LONGTERM in
 gup fast path

On Sat, Feb 29, 2020 at 6:34 AM Ira Weiny <ira.weiny@...el.com> wrote:
>
> On Fri, Feb 28, 2020 at 07:32:29PM +0800, Pingfan Liu wrote:
> > FOLL_LONGTERM suggests a pin which is going to be given to hardware and
> > can't move. It would truncate CMA permanently and should be excluded.
>
> I don't understand what is 'truncated' here?
a pinned page will truncate a continuous area, and prevent CMA to
reclaim the continuous area.
>
> I generally agree with Jason that this is going to be confusing to the user.
Please see the reply in anothe mail.

Thanks,
Pingfan
[...]