linux-kernel - Re: [mm PATCH v5 4/7] mm: Initialize MAX_ORDER_NR_PAGES at a time instead of doing larger sections

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Date:   Fri, 9 Nov 2018 20:02:38 -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 4/7] mm: Initialize MAX_ORDER_NR_PAGES at a time
 instead of doing larger sections

On 18-11-05 13:19:45, Alexander Duyck wrote:
>  	}
> -	first_init_pfn = max(zone->zone_start_pfn, first_init_pfn);
> +
> +	/* If the zone is empty somebody else may have cleared out the zone */
> +	if (!deferred_init_mem_pfn_range_in_zone(&i, zone, &spfn, &epfn,
> +						 first_init_pfn)) {
> +		pgdat_resize_unlock(pgdat, &flags);
> +		pgdat_init_report_one_done();
> +		return 0;

It would make more sense to add goto to the end of this function and report
that in Node X had 0 pages initialized. Otherwise, it will be confusing
why some nodes are not initialized during boot. It is simply because
they do not have deferred pages left to be initialized.


> +	}
>  
>  	/*
> -	 * Initialize and free pages. We do it in two loops: first we initialize
> -	 * struct page, than free to buddy allocator, because while we are
> -	 * freeing pages we can access pages that are ahead (computing buddy
> -	 * page in __free_one_page()).
> +	 * Initialize and free pages in MAX_ORDER sized increments so
> +	 * that we can avoid introducing any issues with the buddy
> +	 * allocator.
>  	 */
> -	for_each_free_mem_pfn_range_in_zone(i, zone, &spfn, &epfn) {
> -		spfn = max_t(unsigned long, first_init_pfn, spfn);
> -		nr_pages += deferred_init_pages(zone, spfn, epfn);
> -	}
> -	for_each_free_mem_pfn_range_in_zone(i, zone, &spfn, &epfn) {
> -		spfn = max_t(unsigned long, first_init_pfn, spfn);
> -		deferred_free_pages(spfn, epfn);
> -	}
> +	while (spfn < epfn)
> +		nr_pages += deferred_init_maxorder(&i, zone, &spfn, &epfn);
> +
>  	pgdat_resize_unlock(pgdat, &flags);
>  
>  	/* Sanity check that the next zone really is unpopulated */
> @@ -1602,9 +1689,9 @@ deferred_grow_zone(struct zone *zone, unsigned int order)
>  {

How about order = max(order, max_order)?

>  	unsigned long nr_pages_needed = ALIGN(1 << order, PAGES_PER_SECTION);


> -	first_init_pfn = max(zone->zone_start_pfn, first_deferred_pfn);
> -
> -	if (first_init_pfn >= pgdat_end_pfn(pgdat)) {
> +	/* If the zone is empty somebody else may have cleared out the zone */
> +	if (!deferred_init_mem_pfn_range_in_zone(&i, zone, &spfn, &epfn,
> +						 first_deferred_pfn)) {
>  		pgdat_resize_unlock(pgdat, &flags);
> -		return false;
> +		return true;

I am OK to change to true here, please also set
pgdat->first_deferred_pfn to ULONG_MAX to indicate that there are no
more deferred pages in this node.


Overall, I like this patch, makes things a lot easier, assuming the
above is addressed:

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

Thank you,
Pasha