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

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Message-Id: <20190212144052.GB20902@rapoport-lnx>
Date:   Tue, 12 Feb 2019 16:40:52 +0200
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     Matthew Wilcox <willy@...radead.org>
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 06:14:18AM -0800, Matthew Wilcox wrote:
> 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.
 
Right, I've completely missed the alignment. Will fix.

-- 
Sincerely yours,
Mike.