linux-kernel - Re: [RFC PATCH] page_ext: create page extension for all memblock memory regions

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Date:   Tue, 17 May 2022 11:25:40 +0300
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Jaewon Kim <jaewon31.kim@...sung.com>, vbabka@...e.cz,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        jaewon31.kim@...il.com, Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [RFC PATCH] page_ext: create page extension for all memblock
 memory regions

On Mon, May 16, 2022 at 05:33:21PM -0700, Andrew Morton wrote:
> On Mon,  9 May 2022 16:43:30 +0900 Jaewon Kim <jaewon31.kim@...sung.com> wrote:
> 
> > The page extension can be prepared for each section. But if the first
> > page is not valid, the page extension for the section was not
> > initialized though there were many other valid pages within the section.

What do you mean by "first page [in a section] is not valid"?
In recent kernels all struct pages in any section should be valid and
properly initialized.
 
> > To support the page extension for all sections, refer to memblock memory
> > regions. If the page is valid use the nid from pfn_to_nid, otherwise use
> > the previous nid.
> > 
> > Also this pagech changed log to include total sections and a section
> > size.
> > 
> > i.e.
> > allocated 100663296 bytes of page_ext for 64 sections (1 section : 0x8000000)
> 
> Cc Joonsoo, who wrote this code.
> Cc Mike, for memblock.
> 
> Thanks.
> 
> > 
> > diff --git a/mm/page_ext.c b/mm/page_ext.c
> > index 2e66d934d63f..506d58b36a1d 100644
> > --- a/mm/page_ext.c
> > +++ b/mm/page_ext.c
> > @@ -381,41 +381,43 @@ static int __meminit page_ext_callback(struct notifier_block *self,
> >  void __init page_ext_init(void)
> >  {
> >  	unsigned long pfn;
> > -	int nid;
> > +	int nid = 0;
> > +	struct memblock_region *rgn;
> > +	int nr_section = 0;
> > +	unsigned long next_section_pfn = 0;
> >  
> >  	if (!invoke_need_callbacks())
> >  		return;
> >  
> > -	for_each_node_state(nid, N_MEMORY) {
> > +	/*
> > +	 * iterate each memblock memory region and do not skip a section having
> > +	 * !pfn_valid(pfn)
> > +	 */
> > +	for_each_mem_region(rgn) {
> >  		unsigned long start_pfn, end_pfn;
> >  
> > -		start_pfn = node_start_pfn(nid);
> > -		end_pfn = node_end_pfn(nid);
> > -		/*
> > -		 * start_pfn and end_pfn may not be aligned to SECTION and the
> > -		 * page->flags of out of node pages are not initialized.  So we
> > -		 * scan [start_pfn, the biggest section's pfn < end_pfn) here.
> > -		 */
> > +		start_pfn = (unsigned long)(rgn->base >> PAGE_SHIFT);
> > +		end_pfn = start_pfn + (unsigned long)(rgn->size >> PAGE_SHIFT);
> > +
> > +		if (start_pfn < next_section_pfn)
> > +			start_pfn = next_section_pfn;
> > +
> >  		for (pfn = start_pfn; pfn < end_pfn;
> >  			pfn = ALIGN(pfn + 1, PAGES_PER_SECTION)) {
> >  
> > -			if (!pfn_valid(pfn))
> > -				continue;
> > -			/*
> > -			 * Nodes's pfns can be overlapping.
> > -			 * We know some arch can have a nodes layout such as
> > -			 * -------------pfn-------------->
> > -			 * N0 | N1 | N2 | N0 | N1 | N2|....
> > -			 */
> > -			if (pfn_to_nid(pfn) != nid)
> > -				continue;
> > +			if (pfn_valid(pfn))
> > +				nid = pfn_to_nid(pfn);
> > +			nr_section++;
> >  			if (init_section_page_ext(pfn, nid))
> >  				goto oom;
> >  			cond_resched();
> >  		}
> > +		next_section_pfn = pfn;
> >  	}
> > +
> >  	hotplug_memory_notifier(page_ext_callback, 0);
> > -	pr_info("allocated %ld bytes of page_ext\n", total_usage);
> > +	pr_info("allocated %ld bytes of page_ext for %d sections (1 section : 0x%x)\n",
> > +		total_usage, nr_section, (1 << SECTION_SIZE_BITS));
> >  	invoke_init_callbacks();
> >  	return;
> >  
> > -- 
> > 2.17.1
> > 

-- 
Sincerely yours,
Mike.