linux-kernel - Re: [PATCH] parisc: use memblock_alloc() instead of custom get

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Date:   Tue, 12 Feb 2019 06:14:18 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Mike Rapoport <rppt@...ux.ibm.com>
Cc:     "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>,
        Helge Deller <deller@....de>, linux-parisc@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] parisc: use memblock_alloc() instead of custom
 get_memblock()

On Tue, Feb 12, 2019 at 03:59:50PM +0200, Mike Rapoport wrote:
> -static void * __init get_memblock(unsigned long size)
> -{
> -	static phys_addr_t search_addr __initdata;
> -	phys_addr_t phys;
> -
> -	if (!search_addr)
> -		search_addr = PAGE_ALIGN(__pa((unsigned long) &_end));
> -	search_addr = ALIGN(search_addr, size);
> -	while (!memblock_is_region_memory(search_addr, size) ||
> -		memblock_is_region_reserved(search_addr, size)) {
> -		search_addr += size;
> -	}
> -	phys = search_addr;

This implies to me that the allocation will be 'size' aligned.

>  		if (!pmd) {
> -			pmd = (pmd_t *) get_memblock(PAGE_SIZE << PMD_ORDER);
> +			pmd = memblock_alloc(PAGE_SIZE << PMD_ORDER,
> +					     SMP_CACHE_BYTES);

So why would this only need to be cacheline aligned?  It's pretty common
for hardware to require that pgd/pud/pmd/pte tables be naturally aligned.

> @@ -700,7 +683,10 @@ static void __init pagetable_init(void)
>  	}
>  #endif
>  
> -	empty_zero_page = get_memblock(PAGE_SIZE);
> +	empty_zero_page = memblock_alloc(PAGE_SIZE, SMP_CACHE_BYTES);

... and surely the zero page also needs to be page aligned, by definition.