Re: [RFC 4/7] mm: add page consistency checker implementation

[David Hildenbrand (Arm)]

> +	/*
> +	 * Size bitmaps to cover the full PFN range including any holes.
> +	 * Holes waste a few bits but a flat bitmap keeps the indexing
> +	 * trivial (pfn - min_pfn) and avoids additional data structures
> +	 * that would themselves be subject to corruption.  This matches
> +	 * the approach used by pageblock_flags.
> +	 */
> +	pc_state.min_pfn = PHYS_PFN(memblock_start_of_DRAM());
> +	pc_state.max_pfn = PHYS_PFN(memblock_end_of_DRAM());
> +	spanned_pfns = pc_state.max_pfn - pc_state.min_pfn;
> +	if (!spanned_pfns || spanned_pfns > UINT_MAX) {
> +		pr_err("PFN span %lu cannot be represented by bitmap APIs, feature disabled\n",
> +		       spanned_pfns);
> +		return;
> +	}
> +
> +	pc_state.db.nbits = spanned_pfns;
> +
> +	bitmap_bytes = BITS_TO_LONGS(pc_state.db.nbits) * sizeof(unsigned long);
> +
> +	pr_info("Initializing: PFN range [%lu-%lu), %u bits (%zu KB per bitmap)\n",
> +		pc_state.min_pfn, pc_state.max_pfn, pc_state.db.nbits,
> +		bitmap_bytes / 1024);
> +
> +	/* Allocate primary bitmap (zeroed by memblock_alloc) */
> +	pc_state.db.bitmap[DUAL_BITMAP_PRIMARY] =
> +		memblock_alloc(bitmap_bytes, SMP_CACHE_BYTES);
> +	if (!pc_state.db.bitmap[DUAL_BITMAP_PRIMARY]) {
> +		pr_err("Failed to allocate primary bitmap, feature disabled\n");
> +		return;
> +	}
> 

One bitmap that covers all sparse memory available at boot.

Conclusion: Just horrible.

-- 
Cheers,

David