2021-04-26 10:11:51

by Vladimir Isaev

Subject: [PATCH] ARC: Use max_high_pfn as a HIGHMEM zone border

Commit 4af22ded0ecf ("arc: fix memory initialization for systems with two
memory banks") fixed highmem, but not for PAE case when highmem is
actually bigger than lowmem.

Signed-off-by: Vladimir Isaev <[email protected]>
Cc: Mike Rapoport <[email protected]>
---
arch/arc/mm/init.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arc/mm/init.c b/arch/arc/mm/init.c
index ce07e697916c..59bad6f94105 100644
--- a/arch/arc/mm/init.c
+++ b/arch/arc/mm/init.c
@@ -157,7 +157,7 @@ void __init setup_arch_memory(void)
min_high_pfn = PFN_DOWN(high_mem_start);
max_high_pfn = PFN_DOWN(high_mem_start + high_mem_sz);

- max_zone_pfn[ZONE_HIGHMEM] = min_low_pfn;
+ max_zone_pfn[ZONE_HIGHMEM] = max_high_pfn;

high_memory = (void *)(min_high_pfn << PAGE_SHIFT);

--
2.16.2

2021-04-26 11:30:16

by Mike Rapoport

Subject: Re: [PATCH] ARC: Use max_high_pfn as a HIGHMEM zone border

Hi,

On Mon, Apr 26, 2021 at 01:10:04PM +0300, Vladimir Isaev wrote:
> Commit 4af22ded0ecf ("arc: fix memory initialization for systems with two
> memory banks") fixed highmem, but not for PAE case when highmem is
> actually bigger than lowmem.
>
> Signed-off-by: Vladimir Isaev <[email protected]>
> Cc: Mike Rapoport <[email protected]>
> ---
> arch/arc/mm/init.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arc/mm/init.c b/arch/arc/mm/init.c
> index ce07e697916c..59bad6f94105 100644
> --- a/arch/arc/mm/init.c
> +++ b/arch/arc/mm/init.c
> @@ -157,7 +157,7 @@ void __init setup_arch_memory(void)
> min_high_pfn = PFN_DOWN(high_mem_start);
> max_high_pfn = PFN_DOWN(high_mem_start + high_mem_sz);
>
> - max_zone_pfn[ZONE_HIGHMEM] = min_low_pfn;
> + max_zone_pfn[ZONE_HIGHMEM] = max_high_pfn;

This is correct with PAE40, but it will break !PAE40 when "highmem" has
lower addresses than lowmem.

It rather should be something like:

if (IS_ENABLED(CONFIG_ARC_HAS_PAE40))
max_zone_pfn[ZONE_HIGHMEM] = max_high_pfn;
else
max_zone_pfn[ZONE_HIGHMEM] = min_low_pfn;


>
> high_memory = (void *)(min_high_pfn << PAGE_SHIFT);
>
> --
> 2.16.2
>

--
Sincerely yours,
Mike.

2021-04-26 11:57:53

by Vladimir Isaev

Subject: RE: [PATCH] ARC: Use max_high_pfn as a HIGHMEM zone border

Hi Mike,

On Mon, April 26, 2021 2:29 PM, Mike Rapoport wrote:
> On Mon, Apr 26, 2021 at 01:10:04PM +0300, Vladimir Isaev wrote:
> > - max_zone_pfn[ZONE_HIGHMEM] = min_low_pfn;
> > + max_zone_pfn[ZONE_HIGHMEM] = max_high_pfn;
>
> This is correct with PAE40, but it will break !PAE40 when "highmem" has lower
> addresses than lowmem.
>
> It rather should be something like:
>
> if (IS_ENABLED(CONFIG_ARC_HAS_PAE40))
> max_zone_pfn[ZONE_HIGHMEM] = max_high_pfn;
> else
> max_zone_pfn[ZONE_HIGHMEM] = min_low_pfn;
>

Not sure if I understand why we should have min_low_pfn here. In !PAE40 case max_high_pfn just will be smaller than min_low_pfn.

Thank you,
Vladimir Isaev

2021-04-26 16:17:09

by Mike Rapoport

Subject: Re: [PATCH] ARC: Use max_high_pfn as a HIGHMEM zone border

On Mon, Apr 26, 2021 at 11:55:00AM +0000, Vladimir Isaev wrote:
> Hi Mike,
>
> On Mon, April 26, 2021 2:29 PM, Mike Rapoport wrote:
> > On Mon, Apr 26, 2021 at 01:10:04PM +0300, Vladimir Isaev wrote:
> > > - max_zone_pfn[ZONE_HIGHMEM] = min_low_pfn;
> > > + max_zone_pfn[ZONE_HIGHMEM] = max_high_pfn;
> >
> > This is correct with PAE40, but it will break !PAE40 when "highmem" has lower
> > addresses than lowmem.
> >
> > It rather should be something like:
> >
> > if (IS_ENABLED(CONFIG_ARC_HAS_PAE40))
> > max_zone_pfn[ZONE_HIGHMEM] = max_high_pfn;
> > else
> > max_zone_pfn[ZONE_HIGHMEM] = min_low_pfn;
> >
>
> Not sure if I understand why we should have min_low_pfn here. In !PAE40
> case max_high_pfn just will be smaller than min_low_pfn.

Hmm, actually, you are right. This should be fine.

--
Sincerely yours,
Mike.

2021-04-26 16:35:07

by Vineet Gupta

Subject: Re: [PATCH] ARC: Use max_high_pfn as a HIGHMEM zone border

On 4/26/21 9:15 AM, Mike Rapoport wrote:
> On Mon, Apr 26, 2021 at 11:55:00AM +0000, Vladimir Isaev wrote:
>> Hi Mike,
>>
>> On Mon, April 26, 2021 2:29 PM, Mike Rapoport wrote:
>>> On Mon, Apr 26, 2021 at 01:10:04PM +0300, Vladimir Isaev wrote:
>>>> - max_zone_pfn[ZONE_HIGHMEM] = min_low_pfn;
>>>> + max_zone_pfn[ZONE_HIGHMEM] = max_high_pfn;
>>> This is correct with PAE40, but it will break !PAE40 when "highmem" has lower
>>> addresses than lowmem.
>>>
>>> It rather should be something like:
>>>
>>> if (IS_ENABLED(CONFIG_ARC_HAS_PAE40))
>>> max_zone_pfn[ZONE_HIGHMEM] = max_high_pfn;
>>> else
>>> max_zone_pfn[ZONE_HIGHMEM] = min_low_pfn;
>>>
>> Not sure if I understand why we should have min_low_pfn here. In !PAE40
>> case max_high_pfn just will be smaller than min_low_pfn.
> Hmm, actually, you are right. This should be fine.

But still worth adding a comment. If this could trip the person who did
the massive cross-arch rework then I don't know what mere mortals would
run into ;-)

-Vineet