linux-kernel - Re: [PATCH] mm/sparse: Consistently do not zero memmap

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Message-ID: <20191031072555.GA13102@dhcp22.suse.cz>
Date:   Thu, 31 Oct 2019 08:25:55 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Vincent Whitchurch <vincent.whitchurch@...s.com>
Cc:     Pavel Tatashin <pasha.tatashin@...een.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "osalvador@...e.de" <osalvador@...e.de>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm/sparse: Consistently do not zero memmap

Vincent, could you give this a try please? It would be even better if
you could add some debugging to measure the overhead. Let me know if you
need any help with a debugging patch.

Thanks!

On Wed 30-10-19 18:31:23, Michal Hocko wrote:
[...]
> What about this? It still aligns to the size but that should be
> correctly done to the section size level.
> 
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 72f010d9bff5..ab1e6175ac9a 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -456,8 +456,7 @@ struct page __init *__populate_section_memmap(unsigned long pfn,
>  	if (map)
>  		return map;
>  
> -	map = memblock_alloc_try_nid(size,
> -					  PAGE_SIZE, addr,
> +	map = memblock_alloc_try_nid(size, size, addr,
>  					  MEMBLOCK_ALLOC_ACCESSIBLE, nid);
>  	if (!map)
>  		panic("%s: Failed to allocate %lu bytes align=0x%lx nid=%d from=%pa\n",
> @@ -474,8 +473,13 @@ static void __init sparse_buffer_init(unsigned long size, int nid)
>  {
>  	phys_addr_t addr = __pa(MAX_DMA_ADDRESS);
>  	WARN_ON(sparsemap_buf);	/* forgot to call sparse_buffer_fini()? */
> +	/*
> +	 * Pre-allocated buffer is mainly used by __populate_section_memmap
> +	 * and we want it to be properly aligned to the section size - this is
> +	 * especially the case for VMEMMAP which maps memmap to PMDs
> +	 */
>  	sparsemap_buf =
> -		memblock_alloc_try_nid_raw(size, PAGE_SIZE,
> +		memblock_alloc_try_nid_raw(size, section_map_size(),
>  						addr,
>  						MEMBLOCK_ALLOC_ACCESSIBLE, nid);
>  	sparsemap_buf_end = sparsemap_buf + size;
> 
> -- 
> Michal Hocko
> SUSE Labs

-- 
Michal Hocko
SUSE Labs