[PATCH 02/11] mm: compaction: introduceisolate_{free,migrate}pages_range().

[Marek Szyprowski]

From: Michal Nazarewicz <mina86@xxxxxxxxxx>

This commit introduces isolate_freepages_range() and
isolate_migratepages_range() functions.  The first one replaces
isolate_freepages_block() and the second one extracts functionality
from isolate_migratepages().

They are more generic and instead of operating on pageblocks operate
on PFN ranges.

Signed-off-by: Michal Nazarewicz <mina86@xxxxxxxxxx>
Signed-off-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
---
 mm/compaction.c |  184 ++++++++++++++++++++++++++++++++++++++-----------------
 1 files changed, 127 insertions(+), 57 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index 899d956..ae73b6f 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -54,55 +54,86 @@ static unsigned long release_freepages(struct list_head *freelist)
 	return count;
 }
 
-/* Isolate free pages onto a private freelist. Must hold zone->lock */
-static unsigned long isolate_freepages_block(struct zone *zone,
-				unsigned long blockpfn,
-				struct list_head *freelist)
+/**
+ * isolate_freepages_range() - isolate free pages, must hold zone->lock.
+ * @zone:	Zone pages are in.
+ * @start_pfn:	The first PFN to start isolating.
+ * @end_pfn:	The one-past-last PFN.
+ * @freelist:	A list to save isolated pages to.
+ *
+ * If @freelist is not provided, holes in range (either non-free pages
+ * or invalid PFNs) are considered an error and function undos its
+ * actions and returns zero.
+ *
+ * If @freelist is provided, function will simply skip non-free and
+ * missing pages and put only the ones isolated on the list.
+ *
+ * Returns number of isolated pages.  This may be more then end_pfn-start_pfn
+ * if end fell in a middle of a free page.
+ */
+static unsigned long
+isolate_freepages_range(struct zone *zone,
+			unsigned long start_pfn, unsigned long end_pfn,
+			struct list_head *freelist)
 {
-	unsigned long zone_end_pfn, end_pfn;
-	int nr_scanned = 0, total_isolated = 0;
-	struct page *cursor;
-
-	/* Get the last PFN we should scan for free pages at */
-	zone_end_pfn = zone->zone_start_pfn + zone->spanned_pages;
-	end_pfn = min(blockpfn + pageblock_nr_pages, zone_end_pfn);
+	unsigned long nr_scanned = 0, total_isolated = 0;
+	unsigned long pfn = start_pfn;
+	struct page *page;
 
-	/* Find the first usable PFN in the block to initialse page cursor */
-	for (; blockpfn < end_pfn; blockpfn++) {
-		if (pfn_valid_within(blockpfn))
-			break;
-	}
-	cursor = pfn_to_page(blockpfn);
+	VM_BUG_ON(!pfn_valid(pfn));
+	page = pfn_to_page(pfn);
 
 	/* Isolate free pages. This assumes the block is valid */
-	for (; blockpfn < end_pfn; blockpfn++, cursor++) {
-		int isolated, i;
-		struct page *page = cursor;
+	while (pfn < end_pfn) {
+		int n = 0, i;
 
-		if (!pfn_valid_within(blockpfn))
-			continue;
-		nr_scanned++;
+		if (!pfn_valid_within(pfn))
+			goto next;
+		++nr_scanned;
 
 		if (!PageBuddy(page))
-			continue;
+			goto next;
 
 		/* Found a free page, break it into order-0 pages */
-		isolated = split_free_page(page);
-		total_isolated += isolated;
-		for (i = 0; i < isolated; i++) {
-			list_add(&page->lru, freelist);
-			page++;
+		n = split_free_page(page);
+		total_isolated += n;
+		if (freelist) {
+			struct page *p = page;
+			for (i = n; i; --i, ++p)
+				list_add(&p->lru, freelist);
 		}
 
-		/* If a page was split, advance to the end of it */
-		if (isolated) {
-			blockpfn += isolated - 1;
-			cursor += isolated - 1;
+next:
+		if (!n) {
+			/* If n == 0, we have isolated no pages. */
+			if (!freelist)
+				goto cleanup;
+			n = 1;
 		}
+
+		/*
+		 * If we pass max order page, we might end up in a different
+		 * vmemmap, so account for that.
+		 */
+		pfn += n;
+		if (pfn & (MAX_ORDER_NR_PAGES - 1))
+			page += n;
+		else
+			page = pfn_to_page(pfn);
 	}
 
 	trace_mm_compaction_isolate_freepages(nr_scanned, total_isolated);
 	return total_isolated;
+
+cleanup:
+	/*
+	 * Undo what we have done so far, and return.  We know all pages from
+	 * [start_pfn, pfn) are free because we have just freed them.  If one of
+	 * the page in the range was not freed, we would end up here earlier.
+	 */
+	for (; start_pfn < pfn; ++start_pfn)
+		__free_page(pfn_to_page(start_pfn));
+	return 0;
 }
 
 /* Returns true if the page is within a block suitable for migration to */
@@ -135,7 +166,7 @@ static void isolate_freepages(struct zone *zone,
 				struct compact_control *cc)
 {
 	struct page *page;
-	unsigned long high_pfn, low_pfn, pfn;
+	unsigned long high_pfn, low_pfn, pfn, zone_end_pfn, end_pfn;
 	unsigned long flags;
 	int nr_freepages = cc->nr_freepages;
 	struct list_head *freelist = &cc->freepages;
@@ -155,6 +186,8 @@ static void isolate_freepages(struct zone *zone,
 	 */
 	high_pfn = min(low_pfn, pfn);
 
+	zone_end_pfn = zone->zone_start_pfn + zone->spanned_pages;
+
 	/*
 	 * Isolate free pages until enough are available to migrate the
 	 * pages on cc->migratepages. We stop searching if the migrate
@@ -191,7 +224,9 @@ static void isolate_freepages(struct zone *zone,
 		isolated = 0;
 		spin_lock_irqsave(&zone->lock, flags);
 		if (suitable_migration_target(page)) {
-			isolated = isolate_freepages_block(zone, pfn, freelist);
+			end_pfn = min(pfn + pageblock_nr_pages, zone_end_pfn);
+			isolated = isolate_freepages_range(zone, pfn,
+					end_pfn, freelist);
 			nr_freepages += isolated;
 		}
 		spin_unlock_irqrestore(&zone->lock, flags);
@@ -250,31 +285,34 @@ typedef enum {
 	ISOLATE_SUCCESS,	/* Pages isolated, migrate */
 } isolate_migrate_t;
 
-/*
- * Isolate all pages that can be migrated from the block pointed to by
- * the migrate scanner within compact_control.
+/**
+ * isolate_migratepages_range() - isolate all migrate-able pages in range.
+ * @zone:	Zone pages are in.
+ * @cc:		Compaction control structure.
+ * @low_pfn:	The first PFN of the range.
+ * @end_pfn:	The one-past-the-last PFN of the range.
+ *
+ * Isolate all pages that can be migrated from the range specified by
+ * [low_pfn, end_pfn).  Returns zero if there is a fatal signal
+ * pending), otherwise PFN of the first page that was not scanned
+ * (which may be both less, equal to or more then end_pfn).
+ *
+ * Assumes that cc->migratepages is empty and cc->nr_migratepages is
+ * zero.
+ *
+ * Other then cc->migratepages and cc->nr_migratetypes this function
+ * does not modify any cc's fields, ie. it does not modify (or read
+ * for that matter) cc->migrate_pfn.
  */
-static isolate_migrate_t isolate_migratepages(struct zone *zone,
-					struct compact_control *cc)
+static unsigned long
+isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
+			   unsigned long low_pfn, unsigned long end_pfn)
 {
-	unsigned long low_pfn, end_pfn;
 	unsigned long last_pageblock_nr = 0, pageblock_nr;
 	unsigned long nr_scanned = 0, nr_isolated = 0;
 	struct list_head *migratelist = &cc->migratepages;
 	isolate_mode_t mode = ISOLATE_ACTIVE|ISOLATE_INACTIVE;
 
-	/* Do not scan outside zone boundaries */
-	low_pfn = max(cc->migrate_pfn, zone->zone_start_pfn);
-
-	/* Only scan within a pageblock boundary */
-	end_pfn = ALIGN(low_pfn + pageblock_nr_pages, pageblock_nr_pages);
-
-	/* Do not cross the free scanner or scan within a memory hole */
-	if (end_pfn > cc->free_pfn || !pfn_valid(low_pfn)) {
-		cc->migrate_pfn = end_pfn;
-		return ISOLATE_NONE;
-	}
-
 	/*
 	 * Ensure that there are not too many pages isolated from the LRU
 	 * list by either parallel reclaimers or compaction. If there are,
@@ -283,12 +321,12 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
 	while (unlikely(too_many_isolated(zone))) {
 		/* async migration should just abort */
 		if (!cc->sync)
-			return ISOLATE_ABORT;
+			return 0;
 
 		congestion_wait(BLK_RW_ASYNC, HZ/10);
 
 		if (fatal_signal_pending(current))
-			return ISOLATE_ABORT;
+			return 0;
 	}
 
 	/* Time to isolate some pages for migration */
@@ -365,17 +403,49 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
 		nr_isolated++;
 
 		/* Avoid isolating too much */
-		if (cc->nr_migratepages == COMPACT_CLUSTER_MAX)
+		if (cc->nr_migratepages == COMPACT_CLUSTER_MAX) {
+			++low_pfn;
 			break;
+		}
 	}
 
 	acct_isolated(zone, cc);
 
 	spin_unlock_irq(&zone->lru_lock);
-	cc->migrate_pfn = low_pfn;
 
 	trace_mm_compaction_isolate_migratepages(nr_scanned, nr_isolated);
 
+	return low_pfn;
+}
+
+/*
+ * Isolate all pages that can be migrated from the block pointed to by
+ * the migrate scanner within compact_control.
+ */
+static isolate_migrate_t isolate_migratepages(struct zone *zone,
+					struct compact_control *cc)
+{
+	unsigned long low_pfn, end_pfn;
+
+	/* Do not scan outside zone boundaries */
+	low_pfn = max(cc->migrate_pfn, zone->zone_start_pfn);
+
+	/* Only scan within a pageblock boundary */
+	end_pfn = ALIGN(low_pfn + pageblock_nr_pages, pageblock_nr_pages);
+
+	/* Do not cross the free scanner or scan within a memory hole */
+	if (end_pfn > cc->free_pfn || !pfn_valid(low_pfn)) {
+		cc->migrate_pfn = end_pfn;
+		return ISOLATE_NONE;
+	}
+
+	/* Perform the isolation */
+	low_pfn = isolate_migratepages_range(zone, cc, low_pfn, end_pfn);
+	if (!low_pfn)
+		return ISOLATE_ABORT;
+
+	cc->migrate_pfn = low_pfn;
+
 	return ISOLATE_SUCCESS;
 }
 
-- 
1.7.1.569.g6f426

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