linux-kernel - Re: [PATCH v4] mm: fix is_pinnable

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Message-ID: <4eea4f5a-0d29-75f3-b93c-fdcb57b4cb8f@nvidia.com>
Date:   Wed, 11 May 2022 21:47:13 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Minchan Kim <minchan@...nel.org>
Cc:     "Paul E. McKenney" <paulmck@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        John Dias <joaodias@...gle.com>,
        David Hildenbrand <david@...hat.com>
Subject: Re: [PATCH v4] mm: fix is_pinnable_page against on cma page

On 5/11/22 20:44, Minchan Kim wrote:
> Thanks for checking, John.
> 
> I don't want to have the READ_ONCE in __get_pfnblock_flags_mask
> atm even though it's an extra memory dereference for specific
> architecutre and specific compiler unless other callsites *do*
> need it.
> 
> We choose the choice(i.e., having __READ_ONCE in is_pinanble_
> page) for *potential* cases(e.g., aggressive LTO for future)
> and if it's an extra memory dereference atm, it would be multiple
> instructions *potentailly* as having more change or different
> compiler and/or arches now or later. It's out of scope in
> this patch.

Agreed!


thanks,
-- 
John Hubbard
NVIDIA