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

Marek Szyprowski
2011-11-18T16:43:09Z

From: Michal Nazarewicz <mina86@mina86.com>

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@mina86.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
---
mm/compaction.c | 170 ++++++++++++++++++++++++++++++++++++-------------------
1 files changed, 111 insertions(+), 59 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index 899d956..6afae0e 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -54,51 +54,64 @@ 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: The first PFN to start isolating.
+ * @end: 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-start
+ * if end fell in a middle of a free page.
+ */
+static unsigned long
+isolate_freepages_range(struct zone *zone,
+ unsigned long start, unsigned long end,
+ 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;
+ 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;
-
- if (!pfn_valid_within(blockpfn))
- continue;
- nr_scanned++;
-
- if (!PageBuddy(page))
- continue;
+ while (pfn < end) {
+ unsigned isolated = 1, i;
+
+ if (!pfn_valid_within(pfn))
+ goto skip;
+ ++nr_scanned;
+
+ if (!PageBuddy(page)) {
+skip:
+ if (freelist)
+ goto next;
+ for (; start < pfn; ++start)
+ __free_page(pfn_to_page(pfn));
+ return 0;
+ }

/* 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++;
+ if (freelist) {
+ struct page *p = page;
+ for (i = isolated; 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:
+ pfn += isolated;
+ page += isolated;
}

trace_mm_compaction_isolate_freepages(nr_scanned, total_isolated);
@@ -135,7 +148,7 @@ 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 +168,8 @@ 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 +206,9 @@ 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 +267,34 @@ 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 +303,12 @@ 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 +385,49 @@ 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