linux-kernel - Re: [PATCH 01/10] mm: page_ref_add_unless() does not trace 'u' argument

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Date:   Wed, 8 Dec 2021 20:25:22 -0500
From:   Pasha Tatashin <pasha.tatashin@...een.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>,
        linux-m68k@...ts.linux-m68k.org,
        Anshuman Khandual <anshuman.khandual@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        william.kucharski@...cle.com,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        schmitzmic@...il.com, Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Roman Gushchin <guro@...com>,
        Muchun Song <songmuchun@...edance.com>, weixugc@...gle.com,
        Greg Thelen <gthelen@...gle.com>,
        David Rientjes <rientjes@...gle.com>,
        Paul Turner <pjt@...gle.com>
Subject: Re: [PATCH 01/10] mm: page_ref_add_unless() does not trace 'u' argument

On Wed, Dec 8, 2021 at 3:55 PM Matthew Wilcox <willy@...radead.org> wrote:
>
> On Wed, Dec 08, 2021 at 08:35:35PM +0000, Pasha Tatashin wrote:
> > In other page_ref_* functions all arguments and returns are traced, but
> > in page_ref_add_unless the 'u' argument which stands for unless boolean
> > is not traced. However, what is more confusing is that in the tracing
> > routine:
> >       __page_ref_mod_unless(struct page *page, int v, int u);
> >
> > The 'u' argument present, but instead a return value is passed into
> > this argument.
> >
> > Add a new template specific for page_ref_add_unless(), and trace all
> > arguments and the return value.
>
> The special casing of '1' for device pages is going away, so NAK
> to this user-visible change.

I can drop this patch, as it really intended to fix existing oddities
and missing info. However, I do not really understand your NAK reason.
Can you please explain about the special casing of "1" for device
pages?

Pasha