On 28/02/2019 19:00, Dave Hansen wrote:
> On 2/28/19 3:28 AM, Steven Price wrote:
>> static int get_level(unsigned long addr, unsigned long end)
>> {
>> /* Add 1 to account for ~0ULL */
>> unsigned long size = (end - addr) + 1;
>> if (size < PMD_SIZE)
>> return 4;
>> else if (size < PUD_SIZE)
>> return 3;
>> else if (size < P4D_SIZE)
>> return 2;
>> else if (size < PGD_SIZE)
>> return 1;
>> return 0;
>> }
>>
>> There are two immediate problems with that:
>>
>> * The "+1" to deal with ~0ULL is fragile
>>
>> * PGD_SIZE isn't what you might expect, it's not defined for most
>> architectures and arm64/x86 use it as the size of the PGD table.
>> Although that's easy enough to fix up.
>>
>> Do you think a function like above would be preferable?
>
> The question still stands of why we *need* the depth/level in the first
> place. As I said, we obviously need it for printing out the "name" of
> the level. Is that it?
That is the only use I'm currently aware of.
>> The other option would of course be to just drop the information from
>> the debugfs file about at which level the holes are. But it can be
>> useful information to see whether there are empty levels in the page
>> table structure. Although this is an area where x86 and arm64 differ
>> currently (x86 explicitly shows the gaps, arm64 doesn't), so if x86
>> doesn't mind losing that functionality that would certainly simplify things!
>
> I think I'd actually be OK with the holes just not showing up. I
> actually find it kinda hard to read sometimes with the holes in there.
> I'd be curious what others think though.
If no-one has any objections to dropping the holes in the output, then I
can rebase on something like below and drop this 'depth' patch.
Steve
----8<----
>From a9eabadfc212389068ec5cc60265c7a55585bb76 Mon Sep 17 00:00:00 2001
From: Steven Price <steven.price@xxxxxxx>
Date: Fri, 1 Mar 2019 10:06:33 +0000
Subject: [PATCH] x86: mm: Hide page table holes in debugfs
For the /sys/kernel/debug/page_tables/ files, rather than outputing a
mostly empty line when a block of memory isn't present just skip the
line. This keeps the output shorter and will help with a future change
switching to using the generic page walk code as we no longer care about
the 'level' that the page table holes are at.
Signed-off-by: Steven Price <steven.price@xxxxxxx>
---
arch/x86/mm/dump_pagetables.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/arch/x86/mm/dump_pagetables.c b/arch/x86/mm/dump_pagetables.c
index e3cdc85ce5b6..a0f4139631dd 100644
--- a/arch/x86/mm/dump_pagetables.c
+++ b/arch/x86/mm/dump_pagetables.c
@@ -304,8 +304,8 @@ static void note_page(struct seq_file *m, struct
pg_state *st,
/*
* Now print the actual finished series
*/
- if (!st->marker->max_lines ||
- st->lines < st->marker->max_lines) {
+ if ((cur & _PAGE_PRESENT) && (!st->marker->max_lines ||
+ st->lines < st->marker->max_lines)) {
pt_dump_seq_printf(m, st->to_dmesg,
"0x%0*lx-0x%0*lx ",
width, st->start_address,
@@ -321,7 +321,9 @@ static void note_page(struct seq_file *m, struct
pg_state *st,
printk_prot(m, st->current_prot, st->level,
st->to_dmesg);
}
- st->lines++;
+ if (cur & _PAGE_PRESENT) {
+ st->lines++;
+ }
/*
* We print markers for special areas of address space,
--
2.20.1
