netdev - Re: [RESEND 4/7] mm/gup: Add FOLL_LONGTERM capability to GUP fast

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Message-ID: <20190325145411.GI16366@iweiny-DESK2.sc.intel.com>
Date:   Mon, 25 Mar 2019 07:54:11 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Jason Gunthorpe <jgg@...pe.ca>,
        Andrew Morton <akpm@...ux-foundation.org>,
        John Hubbard <jhubbard@...dia.com>,
        Michal Hocko <mhocko@...e.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        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>,
        James Hogan <jhogan@...nel.org>, linux-mm <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mips@...r.kernel.org,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        Linux-sh <linux-sh@...r.kernel.org>, sparclinux@...r.kernel.org,
        linux-rdma <linux-rdma@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [RESEND 4/7] mm/gup: Add FOLL_LONGTERM capability to GUP fast

On Mon, Mar 25, 2019 at 03:36:28PM -0700, Dan Williams wrote:
> On Mon, Mar 25, 2019 at 3:22 PM Ira Weiny <ira.weiny@...el.com> wrote:
> [..]
> > FWIW this thread is making me think my original patch which simply implemented
> > get_user_pages_fast_longterm() would be more clear.  There is some evidence
> > that the GUP API was trending that way (see get_user_pages_remote).  That seems
> > wrong but I don't know how to ensure users don't specify the wrong flag.
> 
> What about just making the existing get_user_pages_longterm() have a
> fast path option?

That would work but was not the direction we agreed upon before.[1]

At this point I would rather see this patch set applied, focus on fixing the
filesystem issues, and once that is done determine if FOLL_LONGTERM is needed
in any GUP calls.

Ira

[1] https://lkml.org/lkml/2019/2/11/2038