linux-kernel - Re: [PATCH 03/16] x86, memblock: Add memblock_x86_to

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Date:	Wed, 28 Jul 2010 15:00:36 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Miller <davem@...emloft.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH 03/16] x86, memblock: Add memblock_x86_to_bootmem()

On Thu, 2010-07-22 at 11:43 -0700, Yinghai Lu wrote:
> memblock_x86_to_bootmem() will reserve memblock.reserved.region in bootmem after bootmem is

> +#ifndef CONFIG_NO_BOOTMEM
> +void __init memblock_x86_to_bootmem(u64 start, u64 end)
> +{
> +	int count;
> +	u64 final_start, final_end;
> +	struct memblock_region *r;
> +
> +	/* Take out region array itself */
> +	if (memblock.reserved.regions != memblock_reserved_init_regions)
> +		memblock_free(__pa(memblock.reserved.regions), sizeof(struct memblock_region) * memblock.reserved.max);

So that's why you export memblock_reserved_init_regions...

I really -really- don't like it. First of all, it's really gross to
free the array then walk it. We know it won't race but still ...
especially since you re-do the above every time
memblock_x86_to_bootmem() is called. Is it called more than once ? If
yes, then it's bogus. If not, then why have start,end ?

If you really want to free it, maybe best is to stick something in
mm/memblock.c that kicks in at late init time and does the freeing ?

I'm going to keep the exporting out of my branch for now. If you really
want it, you can always add it to this specific patch, but it sucks.

Ben.

> +	count  = memblock.reserved.cnt;
> +	pr_info("(%d early reservations) ==> bootmem [%010llx-%010llx]\n", count, start, end - 1);
> +	for_each_memblock(reserved, r) {
> +		pr_info("  [%010llx-%010llx] ", (u64)r->base, (u64)r->base + r->size - 1);
> +		final_start = max(start, r->base);
> +		final_end = min(end, r->base + r->size);
> +		if (final_start >= final_end) {
> +			pr_cont("\n");
> +			continue;
> +		}
> +		pr_cont(" ==> [%010llx-%010llx]\n", final_start, final_end - 1);
> +		reserve_bootmem_generic(final_start, final_end - final_start, BOOTMEM_DEFAULT);
> +	}
> +
> +	/* Put region array back ? */
> +	if (memblock.reserved.regions != memblock_reserved_init_regions)
> +		memblock_reserve(__pa(memblock.reserved.regions), sizeof(struct memblock_region) * memblock.reserved.max);
> +}
> +#endif


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