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Subject: Re: [PATCH 09/22] mm, compaction: Use free lists to quickly locate a
 migration source
From:   Vlastimil Babka <vbabka@suse.cz>
To:     Mel Gorman <mgorman@techsingularity.net>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     David Rientjes <rientjes@google.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>
References: <20190118175136.31341-1-mgorman@techsingularity.net>
 <20190118175136.31341-10-mgorman@techsingularity.net>
 <4a6ae9fc-a52b-4300-0edb-a0f4169c314a@suse.cz>
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Date:   Thu, 31 Jan 2019 15:12:25 +0100
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On 1/31/19 2:55 PM, Vlastimil Babka wrote:
> On 1/18/19 6:51 PM, Mel Gorman wrote:
> ...
> 
>> +	for (order = cc->order - 1;
>> +	     order >= PAGE_ALLOC_COSTLY_ORDER && pfn == cc->migrate_pfn && nr_scanned < limit;
>> +	     order--) {
>> +		struct free_area *area = &cc->zone->free_area[order];
>> +		struct list_head *freelist;
>> +		unsigned long flags;
>> +		struct page *freepage;
>> +
>> +		if (!area->nr_free)
>> +			continue;
>> +
>> +		spin_lock_irqsave(&cc->zone->lock, flags);
>> +		freelist = &area->free_list[MIGRATE_MOVABLE];
>> +		list_for_each_entry(freepage, freelist, lru) {
>> +			unsigned long free_pfn;
>> +
>> +			nr_scanned++;
>> +			free_pfn = page_to_pfn(freepage);
>> +			if (free_pfn < high_pfn) {
>> +				update_fast_start_pfn(cc, free_pfn);
> 
> Shouldn't this update go below checking pageblock skip bit? We might be
> caching pageblocks that will be skipped, and also potentially going

Ah that move happens in the next patch.