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Commit c96b9e50 authored by Vlastimil Babka's avatar Vlastimil Babka Committed by Linus Torvalds
Browse files

mm/compaction: cleanup isolate_freepages() 



isolate_freepages() is currently somewhat hard to follow thanks to many
looks like it is related to the 'low_pfn' variable, but in fact it is not.

This patch renames the 'high_pfn' variable to a hopefully less confusing name,
and slightly changes its handling without a functional change. A comment made
obsolete by recent changes is also updated.

[akpm@linux-foundation.org: comment fixes, per Minchan]
[iamjoonsoo.kim@lge.com: cleanups]
Signed-off-by: default avatarVlastimil Babka <vbabka@suse.cz>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Cc: Michal Nazarewicz <mina86@mina86.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Dongjun Shin <d.j.shin@samsung.com>
Cc: Sunghwan Yun <sunghwan.yun@samsung.com>
Signed-off-by: default avatarJoonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 13fb44e4

mm/compaction.c

+27 −29
Original line number Diff line number Diff line
@@ -665,7 +665,10 @@ static void isolate_freepages(struct zone *zone, 
				struct compact_control *cc)

{

	struct page *page;

	unsigned long high_pfn, low_pfn, pfn, z_end_pfn;

	unsigned long block_start_pfn;	/* start of current pageblock */

	unsigned long block_end_pfn;	/* end of current pageblock */

	unsigned long low_pfn;	     /* lowest pfn scanner is able to scan */

	unsigned long next_free_pfn; /* start pfn for scaning at next round */

	int nr_freepages = cc->nr_freepages;

	struct list_head *freelist = &cc->freepages;
@@ -673,32 +676,33 @@ static void isolate_freepages(struct zone *zone, 
	 * Initialise the free scanner. The starting point is where we last

	 * successfully isolated from, zone-cached value, or the end of the

	 * zone when isolating for the first time. We need this aligned to

	 * the pageblock boundary, because we do pfn -= pageblock_nr_pages

	 * in the for loop.

	 * the pageblock boundary, because we do

	 * block_start_pfn -= pageblock_nr_pages in the for loop.

	 * For ending point, take care when isolating in last pageblock of a

	 * a zone which ends in the middle of a pageblock.

	 * The low boundary is the end of the pageblock the migration scanner

	 * is using.

	 */

	pfn = cc->free_pfn & ~(pageblock_nr_pages-1);

	block_start_pfn = cc->free_pfn & ~(pageblock_nr_pages-1);

	block_end_pfn = min(block_start_pfn + pageblock_nr_pages,

						zone_end_pfn(zone));

	low_pfn = ALIGN(cc->migrate_pfn + 1, pageblock_nr_pages);



	/*

	 * Take care that if the migration scanner is at the end of the zone

	 * that the free scanner does not accidentally move to the next zone

	 * in the next isolation cycle.

	 * If no pages are isolated, the block_start_pfn < low_pfn check

	 * will kick in.

	 */

	high_pfn = min(low_pfn, pfn);



	z_end_pfn = zone_end_pfn(zone);

	next_free_pfn = 0;



	/*

	 * Isolate free pages until enough are available to migrate the

	 * pages on cc->migratepages. We stop searching if the migrate

	 * and free page scanners meet or enough free pages are isolated.

	 */

	for (; pfn >= low_pfn && cc->nr_migratepages > nr_freepages;

					pfn -= pageblock_nr_pages) {

	for (; block_start_pfn >= low_pfn && cc->nr_migratepages > nr_freepages;

				block_end_pfn = block_start_pfn,

				block_start_pfn -= pageblock_nr_pages) {

		unsigned long isolated;

		unsigned long end_pfn;



		/*

		 * This can iterate a massively long zone without finding any
@@ -707,7 +711,7 @@ static void isolate_freepages(struct zone *zone, 
		 */

		cond_resched();



		if (!pfn_valid(pfn))

		if (!pfn_valid(block_start_pfn))

			continue;



		/*
@@ -717,7 +721,7 @@ static void isolate_freepages(struct zone *zone, 
		 * i.e. it's possible that all pages within a zones range of

		 * pages do not belong to a single zone.

		 */

		page = pfn_to_page(pfn);

		page = pfn_to_page(block_start_pfn);

		if (page_zone(page) != zone)

			continue;
@@ -730,14 +734,8 @@ static void isolate_freepages(struct zone *zone, 
			continue;



		/* Found a block suitable for isolating free pages from */



		/*

		 * Take care when isolating in last pageblock of a zone which

		 * ends in the middle of a pageblock.

		 */

		end_pfn = min(pfn + pageblock_nr_pages, z_end_pfn);

		isolated = isolate_freepages_block(cc, pfn, end_pfn,

						   freelist, false);

		isolated = isolate_freepages_block(cc, block_start_pfn,

					block_end_pfn, freelist, false);

		nr_freepages += isolated;



		/*
@@ -745,9 +743,9 @@ static void isolate_freepages(struct zone *zone, 
		 * looking for free pages, the search will restart here as

		 * page migration may have returned some pages to the allocator

		 */

		if (isolated) {

		if (isolated && next_free_pfn == 0) {

			cc->finished_update_free = true;

			high_pfn = max(high_pfn, pfn);

			next_free_pfn = block_start_pfn;

		}

	}
@@ -758,10 +756,10 @@ static void isolate_freepages(struct zone *zone, 
	 * If we crossed the migrate scanner, we want to keep it that way

	 * so that compact_finished() may detect this

	 */

	if (pfn < low_pfn)

		cc->free_pfn = max(pfn, zone->zone_start_pfn);

	else

		cc->free_pfn = high_pfn;

	if (block_start_pfn < low_pfn)

		next_free_pfn = cc->migrate_pfn;



	cc->free_pfn = next_free_pfn;

	cc->nr_freepages = nr_freepages;

}