linux-kernel - Re: [PATCH v1 3/5] mm: ptdump: Provide page size to notepage()

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Date:   Fri, 16 Apr 2021 09:12:34 +1000
From:   Daniel Axtens <dja@...ens.net>
To:     Christophe Leroy <christophe.leroy@...roup.eu>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Steven Price <steven.price@....com>, akpm@...ux-foundation.org
Cc:     linux-arch@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-riscv@...ts.infradead.org, x86@...nel.org, linux-mm@...ck.org
Subject: Re: [PATCH v1 3/5] mm: ptdump: Provide page size to notepage()

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