linux-kernel - Re: [PATCH] mm: remove useless code

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Message-ID: <d8228c02-b5c0-47cd-927f-9054d412c7ea@redhat.com>
Date: Mon, 28 Apr 2025 09:17:03 +0200
From: David Hildenbrand <david@...hat.com>
To: Barry Song <21cnbao@...il.com>, Feng Lee <379943137@...com>
Cc: akpm@...ux-foundation.org, ryan.roberts@....com, libang.li@...group.com,
 peterx@...hat.com, maobibo@...ngson.cn, lance.yang@...ux.dev,
 anshuman.khandual@....com, trivial@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: remove useless code

On 27.04.25 10:22, Barry Song wrote:
> On Sun, Apr 27, 2025 at 2:16 PM Feng Lee <379943137@...com> wrote:
>>
>> Remove unused conditional macros.
>>
>> Signed-off-by: Feng Lee <379943137@...com>
>> ---
>>   include/linux/pgtable.h | 2 --
>>   1 file changed, 2 deletions(-)
>>
>> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
>> index b50447ef1c92..47c5a54b7551 100644
>> --- a/include/linux/pgtable.h
>> +++ b/include/linux/pgtable.h
>> @@ -1164,9 +1164,7 @@ static inline void arch_swap_restore(swp_entry_t entry, struct folio *folio)
>>   }
>>   #endif
>>
>> -#ifndef __HAVE_ARCH_PGD_OFFSET_GATE
>>   #define pgd_offset_gate(mm, addr)      pgd_offset(mm, addr)
>> -#endif
> 
> Do you know who else had pgd_offset_gate() before except ia64?
> 
> /* Look up a pgd entry in the gate area.  On IA-64, the gate-area
>     resides in the kernel-mapped segment, hence we use pgd_offset_k()
>     here.  */
> #define pgd_offset_gate(mm, addr) pgd_offset_k(addr)
> 
> btw, do we still
> need pgd_offset_gate() given that nobody needs it now?
> 
>     1   1168  include/linux/pgtable.h <<GLOBAL>>
>               #define pgd_offset_gate(mm, addr) pgd_offset(mm, addr)
> 
>     2   1112  mm/gup.c <<get_gate_page>>
>               pgd = pgd_offset_gate(mm, address);
> 

Right, we should just remove pgd_offset_gate() completely in this patch 
and simply make the single caller use pgd_offset().

I think we can even do:

diff --git a/mm/gup.c b/mm/gup.c
index 84461d384ae2b..05dd87ccce155 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1106,10 +1106,7 @@ static int get_gate_page(struct mm_struct *mm, 
unsigned long address,
         /* user gate pages are read-only */
         if (gup_flags & FOLL_WRITE)
                 return -EFAULT;
-       if (address > TASK_SIZE)
-               pgd = pgd_offset_k(address);
-       else
-               pgd = pgd_offset_gate(mm, address);
+       pgd = pgd_offset(address);
         if (pgd_none(*pgd))
                 return -EFAULT;
         p4d = p4d_offset(pgd, address);

Unless I am missing something important :)

-- 
Cheers,

David / dhildenb