linux-kernel - Re: [RESEND PATCH 0/7] Add FOLL_LONGTERM to GUP fast and use it

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Date:   Wed, 20 Feb 2019 07:19:30 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     ira.weiny@...el.com
Cc:     John Hubbard <jhubbard@...dia.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        "David S. Miller" <davem@...emloft.net>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Rich Felker <dalias@...c.org>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paul.burton@...s.com>,
        James Hogan <jhogan@...nel.org>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-mips@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
        linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
        kvm-ppc@...r.kernel.org, kvm@...r.kernel.org,
        linux-fpga@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-rdma@...r.kernel.org, linux-media@...r.kernel.org,
        linux-scsi@...r.kernel.org, devel@...verdev.osuosl.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
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        devel@...ts.orangefs.org, ceph-devel@...r.kernel.org,
        rds-devel@....oracle.com
Subject: Re: [RESEND PATCH 0/7] Add FOLL_LONGTERM to GUP fast and use it

On Tue, Feb 19, 2019 at 09:30:33PM -0800, ira.weiny@...el.com wrote:
> From: Ira Weiny <ira.weiny@...el.com>
> 
> Resending these as I had only 1 minor comment which I believe we have covered
> in this series.  I was anticipating these going through the mm tree as they
> depend on a cleanup patch there and the IB changes are very minor.  But they
> could just as well go through the IB tree.
> 
> NOTE: This series depends on my clean up patch to remove the write parameter
> from gup_fast_permitted()[1]
> 
> HFI1, qib, and mthca, use get_user_pages_fast() due to it performance
> advantages.  These pages can be held for a significant time.  But
> get_user_pages_fast() does not protect against mapping of FS DAX pages.

This I don't get - if you do lock down long term mappings performance
of the actual get_user_pages call shouldn't matter to start with.

What do I miss?