linux-kernel - Re: [PATCH v5 00/11] Introduces new count-based method for tracking lockless pagetable walks

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Date:   Thu, 03 Oct 2019 18:38:40 -0300
From:   Leonardo Bras <leonardo@...ux.ibm.com>
To:     John Hubbard <jhubbard@...dia.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Song Liu <songliubraving@...com>, Michal Hocko <mhocko@...e.com>,
        "Dmitry V. Levin" <ldv@...linux.org>,
        Keith Busch <keith.busch@...el.com>, linux-mm@...ck.org,
        Paul Mackerras <paulus@...ba.org>,
        Christoph Lameter <cl@...ux.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Elena Reshetova <elena.reshetova@...el.com>,
        linux-arch@...r.kernel.org, Santosh Sivaraj <santosh@...six.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Vlastimil Babka <vbabka@...e.cz>,
        Mahesh Salgaonkar <mahesh@...ux.vnet.ibm.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        Arnd Bergmann <arnd@...db.de>, Jann Horn <jannh@...gle.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        kvm-ppc@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Reza Arbab <arbab@...ux.ibm.com>,
        Allison Randal <allison@...utok.net>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org,
        Logan Gunthorpe <logang@...tatee.com>,
        Souptick Joarder <jrdr.linux@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linuxppc-dev@...ts.ozlabs.org, Roman Gushchin <guro@...com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH v5 00/11] Introduces new count-based method for tracking
 lockless pagetable walks

On Thu, 2019-10-03 at 13:49 -0700, John Hubbard wrote:
> Yes. And to clarify, I was assuming that the changes to mm/gup.c were 
> required in order to accomplish your goals. Given that assumption, I 
> wanted the generic code to be "proper", and that's what that feedback
> is about.

You assumed right. On my counting approach it's necessary count all
'lockless pagetable walks', including the ones in generic code.

And, I think even without the counting approach, it was a good way
focus this 'lockless pagetable walk' routine in a single place.

> 
> Although the other questions about file-backed THP
> make it sound like some rethinking across the board is required now.

Yeap, I need to better understand how the file-backed THP problem
works.

Thanks,

Leonardo Brás

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