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From:   Daniel Axtens <dja@axtens.net>
To:     Christophe Leroy <christophe.leroy@csgroup.eu>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Steven Price <steven.price@arm.com>, akpm@linux-foundation.org
Cc:     linux-arch@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linux-riscv@lists.infradead.org, x86@kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH v1 3/5] mm: ptdump: Provide page size to notepage()
In-Reply-To: <1ef6b954fb7b0f4dfc78820f1e612d2166c13227.1618506910.git.christophe.leroy@csgroup.eu>
References: <cover.1618506910.git.christophe.leroy@csgroup.eu> <1ef6b954fb7b0f4dfc78820f1e612d2166c13227.1618506910.git.christophe.leroy@csgroup.eu>
Date:   Fri, 16 Apr 2021 09:12:34 +1000
Message-ID: <8735vr16sd.fsf@dja-thinkpad.axtens.net>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

Hi Christophe,

>  static void note_page(struct ptdump_state *pt_st, unsigned long addr, int level,
> -		      u64 val)
> +		      u64 val, unsigned long page_size)

Compilers can warn about unused parameters at -Wextra level.  However,
reading scripts/Makefile.extrawarn it looks like the warning is
explicitly _disabled_ in the kernel at W=1 and not reenabled at W=2 or
W=3. So I guess this is fine...

> @@ -126,7 +126,7 @@ static int ptdump_hole(unsigned long addr, unsigned long next,
>  {
>  	struct ptdump_state *st = walk->private;
>  
> -	st->note_page(st, addr, depth, 0);
> +	st->note_page(st, addr, depth, 0, 0);

I know it doesn't matter at this point, but I'm not really thrilled by
the idea of passing 0 as the size here. Doesn't the hole have a known
page size?

>  
>  	return 0;
>  }
> @@ -153,5 +153,5 @@ void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm, pgd_t *pgd)
>  	mmap_read_unlock(mm);
>  
>  	/* Flush out the last page */
> -	st->note_page(st, 0, -1, 0);
> +	st->note_page(st, 0, -1, 0, 0);

I'm more OK with the idea of passing 0 as the size when the depth is -1
(don't know): if we don't know the depth we conceptually can't know the
page size.

Regards,
Daniel