linux-kernel - Re: [PATCH v2 03/11] mm/gup: Applies counting method to monitor gup_pgd

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Date:   Mon, 23 Sep 2019 18:01:54 -0300
From:   Leonardo Bras <leonardo@...ux.ibm.com>
To:     John Hubbard <jhubbard@...dia.com>, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, Linux-MM <linux-mm@...ck.org>
Cc:     Jason Gunthorpe <jgg@...pe.ca>,
        Thomas Gleixner <tglx@...utronix.de>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        YueHaibing <yuehaibing@...wei.com>,
        Keith Busch <keith.busch@...el.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Mahesh Salgaonkar <mahesh@...ux.vnet.ibm.com>,
        Richard Fontana <rfontana@...hat.com>,
        Paul Mackerras <paulus@...ba.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Ganesh Goudar <ganeshgr@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ira Weiny <ira.weiny@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Allison Randal <allison@...utok.net>
Subject: Re: [PATCH v2 03/11] mm/gup: Applies counting method to monitor
 gup_pgd_range

On Mon, 2019-09-23 at 13:27 -0700, John Hubbard wrote:
> I'd also like a second opinion from the "core" -mm maintainers, but it seems like
> there is now too much code around the gup_pgd_range() call. Especially since there
> are two places where it's called--did you forget the other one in 
> __get_user_pages_fast(), btw??
> 
Oh, sorry, I missed this one. I will put it on v3.
(Also I will make sure to include linux-mm on v3.)

> Maybe the irq handling and atomic counting should be moved into start/finish
> calls, like this:
> 
>      start_gup_fast_walk()
>      gup_pgd_range()
>      finish_gup_fast_walk()

There are cases where interrupt disable/enable is not done around the
lockless pagetable walk.
It may come from functions called above on stack, that's why I opted it
to be only the atomic operation.

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