From: Steven Price <steven.price@arm.com>
To: Mark Rutland <Mark.Rutland@arm.com>
Cc: "x86@kernel.org" <x86@kernel.org>,
"Arnd Bergmann" <arnd@arndb.de>,
"Ard Biesheuvel" <ard.biesheuvel@linaro.org>,
"Peter Zijlstra" <peterz@infradead.org>,
"Catalin Marinas" <Catalin.Marinas@arm.com>,
"Dave Hansen" <dave.hansen@linux.intel.com>,
"Will Deacon" <Will.Deacon@arm.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"Jérôme Glisse" <jglisse@redhat.com>,
"Ingo Molnar" <mingo@redhat.com>,
"Borislav Petkov" <bp@alien8.de>,
"Andy Lutomirski" <luto@kernel.org>,
"H. Peter Anvin" <hpa@zytor.com>,
"James Morse" <James.Morse@arm.com>,
"Thomas Gleixner" <tglx@linutronix.de>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH 06/13] mm: pagewalk: Add 'depth' parameter to pte_hole
Date: Mon, 18 Feb 2019 15:23:22 +0000 [thread overview]
Message-ID: <7b0c6eed-102e-ff79-0f65-16bcec043a09@arm.com> (raw)
In-Reply-To: <20190218112350.GE8036@lakrids.cambridge.arm.com>
On 18/02/2019 11:23, Mark Rutland wrote:
> On Fri, Feb 15, 2019 at 05:02:27PM +0000, Steven Price wrote:
>> +/* If the p4ds are actually just pgds then we should report a depth
>> + * of 0 not 1 (as a missing entry is really a missing pgd
>> + */
>
> Nit: comment style violation. This should look like:
> should be:
>
> /*
> * If the p4ds are actually just pgds then we should report a depth
> * of 0 not 1 (as a missing entry is really a missing pgd
> */
>
>> +int depth = (PTRS_PER_P4D == 1)?0:1;
>
> Nit: the ternary should have spacing.
>
> We don't seem to do this at any other level that could be folded, so why
> does p4d need special care?
>
> For example, what happens on arm64 when using 64K pages and 3 level
> paging, where puds are folded into pgds?
>
> Thanks,
> Mark.
Yes, you are entirely correct I've missed the other potential foldings.
I somehow imagined that p4d was special and was folded the opposite
direction (I'm not sure why!).
The best solution I can come up with is a function which will convert
from the level the entry is found at, back to the 'real' level the entry
was missing at. This is needed to produce the correct output in the
debugfs file. Something like:
static int real_depth(int depth)
{
if (depth == 3 && PTRS_PER_PMD == 1)
depth = 2;
if (depth == 2 && PTRS_PER_PUD == 1)
depth = 1;
if (depth == 1 && PTRS_PER_P4D == 1)
depth = 0;
return depth;
}
This should of course get folded by the compiler and not actually
generate any code.
Thanks,
Steve
next prev parent reply other threads:[~2019-02-18 15:23 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-15 17:02 [PATCH 00/13] Convert x86 & arm64 to use generic page walk Steven Price
2019-02-15 17:02 ` [PATCH 01/13] arm64: mm: Add p?d_large() definitions Steven Price
2019-02-18 11:16 ` Mark Rutland
2019-02-18 11:29 ` Peter Zijlstra
2019-02-18 13:45 ` Mark Rutland
2019-02-18 14:11 ` Steven Price
2019-02-18 14:29 ` Mark Rutland
2019-02-18 15:06 ` Peter Zijlstra
2019-02-18 15:30 ` Steven Price
2019-02-18 17:04 ` Mark Rutland
2019-02-18 17:22 ` Steven Price
2019-02-15 17:02 ` [PATCH 02/13] x86/mm: " Steven Price
2019-02-15 17:02 ` [PATCH 03/13] mm: Add generic p?d_large() macros Steven Price
2019-02-18 11:14 ` Mark Rutland
2019-02-18 12:53 ` Peter Zijlstra
2019-02-18 14:20 ` Steven Price
2019-02-18 11:31 ` Peter Zijlstra
2019-02-18 14:19 ` Steven Price
2019-02-19 3:44 ` Liang, Kan
2019-02-20 13:56 ` Steven Price
2019-02-15 17:02 ` [PATCH 04/13] mm: pagewalk: Add p4d_entry() and pgd_entry() Steven Price
2019-02-15 17:02 ` [PATCH 05/13] mm: pagewalk: Allow walking without vma Steven Price
2019-02-15 17:02 ` [PATCH 06/13] mm: pagewalk: Add 'depth' parameter to pte_hole Steven Price
2019-02-18 11:23 ` Mark Rutland
2019-02-18 15:23 ` Steven Price [this message]
2019-02-20 11:35 ` William Kucharski
2019-02-20 14:10 ` Steven Price
2019-02-15 17:02 ` [PATCH 07/13] mm: pagewalk: Add test_p?d callbacks Steven Price
2019-02-15 17:02 ` [PATCH 08/13] arm64: mm: Convert mm/dump.c to use walk_page_range() Steven Price
2019-02-15 17:02 ` [PATCH 09/13] x86/mm: Point to struct seq_file from struct pg_state Steven Price
2019-02-15 17:02 ` [PATCH 10/13] x86/mm+efi: Convert ptdump_walk_pgd_level() to take a mm_struct Steven Price
2019-02-15 17:02 ` [PATCH 11/13] x86/mm: Convert ptdump_walk_pgd_level_debugfs() to take an mm_struct Steven Price
2019-02-15 17:02 ` [PATCH 12/13] x86/mm: Convert ptdump_walk_pgd_level_core() " Steven Price
2019-02-15 17:02 ` [PATCH 13/13] x86: mm: Convert dump_pagetables to use walk_page_range Steven Price
2019-02-15 17:16 ` Dave Hansen
2019-02-15 17:32 ` Steven Price
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