linux-kernel - Re: [PATCH 2/2] LoongArch: Use static defined zero page rather than allocated

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Message-ID: <c8339828-daa8-2426-49cb-dd59aa1487bb@loongson.cn>
Date:   Tue, 5 Sep 2023 19:05:40 +0800
From:   bibo mao <maobibo@...ngson.cn>
To:     Huacai Chen <chenhuacai@...nel.org>
Cc:     WANG Xuerui <kernel@...0n.name>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] LoongArch: Use static defined zero page rather than
 allocated



在 2023/9/5 18:59, Huacai Chen 写道:
> Hi, Bibo,
> 
> On Tue, Sep 5, 2023 at 4:01 PM Bibo Mao <maobibo@...ngson.cn> wrote:
>>
>> Like other popular architectures, zero page is defined in kernel
>> BSS code segment, rather than dynamically alloted page. It is
>> simpler.
>>
>> Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
>> ---
>>  arch/loongarch/include/asm/mmzone.h  |  2 --
>>  arch/loongarch/include/asm/pgtable.h |  6 ++----
>>  arch/loongarch/kernel/numa.c         |  1 -
>>  arch/loongarch/mm/init.c             | 21 +--------------------
>>  4 files changed, 3 insertions(+), 27 deletions(-)
>>
>> diff --git a/arch/loongarch/include/asm/mmzone.h b/arch/loongarch/include/asm/mmzone.h
>> index fe67d0b4b33d..2b9a90727e19 100644
>> --- a/arch/loongarch/include/asm/mmzone.h
>> +++ b/arch/loongarch/include/asm/mmzone.h
>> @@ -13,6 +13,4 @@ extern struct pglist_data *node_data[];
>>
>>  #define NODE_DATA(nid) (node_data[(nid)])
>>
>> -extern void setup_zero_pages(void);
>> -
>>  #endif /* _ASM_MMZONE_H_ */
>> diff --git a/arch/loongarch/include/asm/pgtable.h b/arch/loongarch/include/asm/pgtable.h
>> index 342c5f9c25d2..70bd57daf42a 100644
>> --- a/arch/loongarch/include/asm/pgtable.h
>> +++ b/arch/loongarch/include/asm/pgtable.h
>> @@ -70,10 +70,8 @@ struct vm_area_struct;
>>   * for zero-mapped memory areas etc..
>>   */
>>
>> -extern unsigned long empty_zero_page;
>> -
>> -#define ZERO_PAGE(vaddr) \
>> -       (virt_to_page((void *)(empty_zero_page)))
>> +extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];
>> +#define ZERO_PAGE(vaddr)       ((void)(vaddr), virt_to_page(empty_zero_page))
> Can we simply use virt_to_page(empty_zero_page) here? Only x86 does it
> like this now.
will do in next patch.

Regards
Bibo Mao
> 
> Huacai
>>
>>  /*
>>   * TLB refill handlers may also map the vmalloc area into xkvrange.
>> diff --git a/arch/loongarch/kernel/numa.c b/arch/loongarch/kernel/numa.c
>> index 708665895b47..6f464d49f0c2 100644
>> --- a/arch/loongarch/kernel/numa.c
>> +++ b/arch/loongarch/kernel/numa.c
>> @@ -470,7 +470,6 @@ void __init mem_init(void)
>>  {
>>         high_memory = (void *) __va(get_num_physpages() << PAGE_SHIFT);
>>         memblock_free_all();
>> -       setup_zero_pages();     /* This comes from node 0 */
>>  }
>>
>>  int pcibus_to_node(struct pci_bus *bus)
>> diff --git a/arch/loongarch/mm/init.c b/arch/loongarch/mm/init.c
>> index 8ec668f97b00..628ebe42b519 100644
>> --- a/arch/loongarch/mm/init.c
>> +++ b/arch/loongarch/mm/init.c
>> @@ -35,27 +35,9 @@
>>  #include <asm/pgalloc.h>
>>  #include <asm/tlb.h>
>>
>> -unsigned long empty_zero_page;
>> +unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)] __page_aligned_bss;
>>  EXPORT_SYMBOL(empty_zero_page);
>>
>> -void setup_zero_pages(void)
>> -{
>> -       unsigned int order, i;
>> -       struct page *page;
>> -
>> -       order = 0;
>> -
>> -       empty_zero_page = __get_free_pages(GFP_KERNEL | __GFP_ZERO, order);
>> -       if (!empty_zero_page)
>> -               panic("Oh boy, that early out of memory?");
>> -
>> -       page = virt_to_page((void *)empty_zero_page);
>> -       split_page(page, order);
>> -       for (i = 0; i < (1 << order); i++, page++)
>> -               mark_page_reserved(page);
>> -
>> -}
>> -
>>  void copy_user_highpage(struct page *to, struct page *from,
>>         unsigned long vaddr, struct vm_area_struct *vma)
>>  {
>> @@ -99,7 +81,6 @@ void __init mem_init(void)
>>         high_memory = (void *) __va(max_low_pfn << PAGE_SHIFT);
>>
>>         memblock_free_all();
>> -       setup_zero_pages();     /* Setup zeroed pages.  */
>>  }
>>  #endif /* !CONFIG_NUMA */
>>
>> --
>> 2.27.0
>>
>>