linux-kernel - Re: [PATCH] mm: sparse: Skip no-map regions in memblocks

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Message-ID: <20190723070642.GC4552@dhcp22.suse.cz>
Date:   Tue, 23 Jul 2019 09:06:42 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     KarimAllah Ahmed <karahmed@...zon.de>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Pavel Tatashin <pasha.tatashin@...cle.com>,
        Oscar Salvador <osalvador@...e.de>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Baoquan He <bhe@...hat.com>, Qian Cai <cai@....pw>,
        Wei Yang <richard.weiyang@...il.com>,
        Logan Gunthorpe <logang@...tatee.com>
Subject: Re: [PATCH] mm: sparse: Skip no-map regions in memblocks_present

On Fri 12-07-19 10:51:31, KarimAllah Ahmed wrote:
> Do not mark regions that are marked with nomap to be present, otherwise
> these memblock cause unnecessarily allocation of metadata.

This begs for much more information. How come nomap regions are in
usable memblocks? What if memblock allocator used that memory?
In other words, shouldn't nomap (an unusable memory iirc) be in reserved
memblocks or removed altogethher?

> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Pavel Tatashin <pasha.tatashin@...cle.com>
> Cc: Oscar Salvador <osalvador@...e.de>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Mike Rapoport <rppt@...ux.ibm.com>
> Cc: Baoquan He <bhe@...hat.com>
> Cc: Qian Cai <cai@....pw>
> Cc: Wei Yang <richard.weiyang@...il.com>
> Cc: Logan Gunthorpe <logang@...tatee.com>
> Cc: linux-mm@...ck.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: KarimAllah Ahmed <karahmed@...zon.de>
> ---
>  mm/sparse.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/mm/sparse.c b/mm/sparse.c
> index fd13166..33810b6 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -256,6 +256,10 @@ void __init memblocks_present(void)
>  	struct memblock_region *reg;
>  
>  	for_each_memblock(memory, reg) {
> +
> +		if (memblock_is_nomap(reg))
> +			continue;
> +
>  		memory_present(memblock_get_region_node(reg),
>  			       memblock_region_memory_base_pfn(reg),
>  			       memblock_region_memory_end_pfn(reg));
> -- 
> 2.7.4

-- 
Michal Hocko
SUSE Labs