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Subject: Re: [PATCH 5/5] arch: simplify several early memory allocations
To:     Mike Rapoport <rppt@linux.ibm.com>, linux-kernel@vger.kernel.org
Cc:     Michal Hocko <mhocko@suse.com>, linux-sh@vger.kernel.org,
        linux-mm@kvack.org, Rich Felker <dalias@libc.org>,
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        Jonas Bonn <jonas@southpole.se>, linux-c6x-dev@linux-c6x.org,
        Yoshinori Sato <ysato@users.sourceforge.jp>,
        Russell King <linux@armlinux.org.uk>,
        Mark Salter <msalter@redhat.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>,
        openrisc@lists.librecores.org, Greentime Hu <green.hu@gmail.com>,
        Stafford Horne <shorne@gmail.com>,
        Guan Xuetao <gxt@pku.edu.cn>,
        linux-arm-kernel@lists.infradead.org,
        Michal Simek <monstr@monstr.eu>,
        Andrew Morton <akpm@linux-foundation.org>,
        linuxppc-dev@lists.ozlabs.org,
        "David S. Miller" <davem@davemloft.net>
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From:   Christophe LEROY <christophe.leroy@c-s.fr>
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Date:   Mon, 26 Nov 2018 08:03:55 +0100
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Le 25/11/2018 à 22:44, Mike Rapoport a écrit :
> There are several early memory allocations in arch/ code that use
> memblock_phys_alloc() to allocate memory, convert the returned physical
> address to the virtual address and then set the allocated memory to zero.
> 
> Exactly the same behaviour can be achieved simply by calling
> memblock_alloc(): it allocates the memory in the same way as
> memblock_phys_alloc(), then it performs the phys_to_virt() conversion and
> clears the allocated memory.
> 
> Replace the longer sequence with a simpler call to memblock_alloc().
> 
> Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
> ---
>   arch/arm/mm/mmu.c                     |  4 +---
>   arch/c6x/mm/dma-coherent.c            |  9 ++-------
>   arch/nds32/mm/init.c                  | 12 ++++--------
>   arch/powerpc/kernel/setup-common.c    |  4 ++--
>   arch/powerpc/mm/pgtable_32.c          |  4 +---
>   arch/powerpc/mm/ppc_mmu_32.c          |  3 +--
>   arch/powerpc/platforms/powernv/opal.c |  3 +--
>   arch/sparc/kernel/prom_64.c           |  7 ++-----
>   arch/sparc/mm/init_64.c               |  9 +++------
>   arch/unicore32/mm/mmu.c               |  4 +---
>   10 files changed, 18 insertions(+), 41 deletions(-)
> 
[...]

> diff --git a/arch/powerpc/mm/pgtable_32.c b/arch/powerpc/mm/pgtable_32.c
> index bda3c6f..9931e68 100644
> --- a/arch/powerpc/mm/pgtable_32.c
> +++ b/arch/powerpc/mm/pgtable_32.c
> @@ -50,9 +50,7 @@ __ref pte_t *pte_alloc_one_kernel(struct mm_struct *mm, unsigned long address)
>   	if (slab_is_available()) {
>   		pte = (pte_t *)__get_free_page(GFP_KERNEL|__GFP_ZERO);
>   	} else {
> -		pte = __va(memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE));
> -		if (pte)
> -			clear_page(pte);
> +		pte = memblock_alloc(PAGE_SIZE, PAGE_SIZE);

memblock_alloc() uses memset to zeroize the block.

clear_page() is more performant than memset().


Christophe

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