linux-kernel - Re: [mm PATCH v5 7/7] mm: Use common iterator for deferred_init_pages and deferred_free

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Message-ID: <20181110041338.7ttram7po7a2ssz7@xakep.localdomain>
Date:   Fri, 9 Nov 2018 23:13:38 -0500
From:   Pavel Tatashin <pasha.tatashin@...een.com>
To:     Alexander Duyck <alexander.h.duyck@...ux.intel.com>
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        sparclinux@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nvdimm@...ts.01.org, davem@...emloft.net,
        pavel.tatashin@...rosoft.com, mhocko@...e.com, mingo@...nel.org,
        kirill.shutemov@...ux.intel.com, dan.j.williams@...el.com,
        dave.jiang@...el.com, rppt@...ux.vnet.ibm.com, willy@...radead.org,
        vbabka@...e.cz, khalid.aziz@...cle.com, ldufour@...ux.vnet.ibm.com,
        mgorman@...hsingularity.net, yi.z.zhang@...ux.intel.com
Subject: Re: [mm PATCH v5 7/7] mm: Use common iterator for
 deferred_init_pages and deferred_free_pages

On 18-11-05 13:20:01, Alexander Duyck wrote:
> +static unsigned long __next_pfn_valid_range(unsigned long *i,
> +					    unsigned long end_pfn)
>  {
> -	if (!pfn_valid_within(pfn))
> -		return false;
> -	if (!(pfn & (pageblock_nr_pages - 1)) && !pfn_valid(pfn))
> -		return false;
> -	return true;
> +	unsigned long pfn = *i;
> +	unsigned long count;
> +
> +	while (pfn < end_pfn) {
> +		unsigned long t = ALIGN(pfn + 1, pageblock_nr_pages);
> +		unsigned long pageblock_pfn = min(t, end_pfn);
> +
> +#ifndef CONFIG_HOLES_IN_ZONE
> +		count = pageblock_pfn - pfn;
> +		pfn = pageblock_pfn;
> +		if (!pfn_valid(pfn))
> +			continue;
> +#else
> +		for (count = 0; pfn < pageblock_pfn; pfn++) {
> +			if (pfn_valid_within(pfn)) {
> +				count++;
> +				continue;
> +			}
> +
> +			if (count)
> +				break;
> +		}
> +
> +		if (!count)
> +			continue;
> +#endif
> +		*i = pfn;
> +		return count;
> +	}
> +
> +	return 0;
>  }
>  
> +#define for_each_deferred_pfn_valid_range(i, start_pfn, end_pfn, pfn, count) \
> +	for (i = (start_pfn),						     \
> +	     count = __next_pfn_valid_range(&i, (end_pfn));		     \
> +	     count && ({ pfn = i - count; 1; });			     \
> +	     count = __next_pfn_valid_range(&i, (end_pfn)))

Can this be improved somehow? It took me a while to understand this
piece of code. i is actually end of block, and not an index by PFN, ({pfn = i - count; 1;}) is
simply hard to parse. Why can't we make __next_pfn_valid_range() to
return both end and a start of a block?

The rest is good:

Reviewed-by: Pavel Tatashin <pasha.tatashin@...een.com>

Thank you,
Pasha