[PATCH v6 05/13] mm, compaction: move pageblock checks up from isolate_migratepages_range()
From: Vlastimil Babka
Date: Mon Aug 04 2014 - 04:59:28 EST
isolate_migratepages_range() is the main function of the compaction scanner,
called either on a single pageblock by isolate_migratepages() during regular
compaction, or on an arbitrary range by CMA's __alloc_contig_migrate_range().
It currently perfoms two pageblock-wide compaction suitability checks, and
because of the CMA callpath, it tracks if it crossed a pageblock boundary in
order to repeat those checks.
However, closer inspection shows that those checks are always true for CMA:
- isolation_suitable() is true because CMA sets cc->ignore_skip_hint to true
- migrate_async_suitable() check is skipped because CMA uses sync compaction
We can therefore move the compaction-specific checks to isolate_migratepages()
and simplify isolate_migratepages_range(). Furthermore, we can mimic the
freepage scanner family of functions, which has isolate_freepages_block()
function called both by compaction from isolate_freepages() and by CMA from
isolate_freepages_range(), where each use-case adds own specific glue code.
This allows further code simplification.
Thus, we rename isolate_migratepages_range() to isolate_migratepages_block()
and limit its functionality to a single pageblock (or its subset). For CMA,
a new different isolate_migratepages_range() is created as a CMA-specific
wrapper for the _block() function. The checks specific to compaction are moved
to isolate_migratepages(). As part of the unification of these two families of
functions, we remove the redundant zone parameter where applicable, since zone
pointer is already passed in cc->zone.
Furthermore, going back to compact_zone() and compact_finished() when pageblock
is found unsuitable (now by isolate_migratepages()) is wasteful - the checks
are meant to skip pageblocks quickly. The patch therefore also introduces a
simple loop into isolate_migratepages() so that it does not return immediately
on failed pageblock checks, but keeps going until isolate_migratepages_range()
gets called once. Similarily to isolate_freepages(), the function periodically
checks if it needs to reschedule or abort async compaction.
Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Acked-by: Mel Gorman <mgorman@xxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Michal Nazarewicz <mina86@xxxxxxxxxx>
Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
---
mm/compaction.c | 235 +++++++++++++++++++++++++++++++++-----------------------
mm/internal.h | 4 +-
mm/page_alloc.c | 3 +-
3 files changed, 141 insertions(+), 101 deletions(-)
diff --git a/mm/compaction.c b/mm/compaction.c
index 9484a4f..0168786 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -132,7 +132,7 @@ void reset_isolation_suitable(pg_data_t *pgdat)
*/
static void update_pageblock_skip(struct compact_control *cc,
struct page *page, unsigned long nr_isolated,
- bool set_unsuitable, bool migrate_scanner)
+ bool migrate_scanner)
{
struct zone *zone = cc->zone;
unsigned long pfn;
@@ -146,12 +146,7 @@ static void update_pageblock_skip(struct compact_control *cc,
if (nr_isolated)
return;
- /*
- * Only skip pageblocks when all forms of compaction will be known to
- * fail in the near future.
- */
- if (set_unsuitable)
- set_pageblock_skip(page);
+ set_pageblock_skip(page);
pfn = page_to_pfn(page);
@@ -180,7 +175,7 @@ static inline bool isolation_suitable(struct compact_control *cc,
static void update_pageblock_skip(struct compact_control *cc,
struct page *page, unsigned long nr_isolated,
- bool set_unsuitable, bool migrate_scanner)
+ bool migrate_scanner)
{
}
#endif /* CONFIG_COMPACTION */
@@ -345,8 +340,7 @@ isolate_fail:
/* Update the pageblock-skip if the whole pageblock was scanned */
if (blockpfn == end_pfn)
- update_pageblock_skip(cc, valid_page, total_isolated, true,
- false);
+ update_pageblock_skip(cc, valid_page, total_isolated, false);
count_compact_events(COMPACTFREE_SCANNED, nr_scanned);
if (total_isolated)
@@ -451,40 +445,34 @@ static bool too_many_isolated(struct zone *zone)
}
/**
- * isolate_migratepages_range() - isolate all migrate-able pages in range.
- * @zone: Zone pages are in.
+ * isolate_migratepages_block() - isolate all migrate-able pages within
+ * a single pageblock
* @cc: Compaction control structure.
- * @low_pfn: The first PFN of the range.
- * @end_pfn: The one-past-the-last PFN of the range.
- * @unevictable: true if it allows to isolate unevictable pages
+ * @low_pfn: The first PFN to isolate
+ * @end_pfn: The one-past-the-last PFN to isolate, within same pageblock
+ * @isolate_mode: Isolation mode to be used.
*
* 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.
+ * [low_pfn, end_pfn). The range is expected to be within same pageblock.
+ * 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
+ * than end_pfn).
*
- * Apart from cc->migratepages and cc->nr_migratetypes this function
- * does not modify any cc's fields, in particular it does not modify
- * (or read for that matter) cc->migrate_pfn.
+ * The pages are isolated on cc->migratepages list (not required to be empty),
+ * and cc->nr_migratepages is updated accordingly. The cc->migrate_pfn field
+ * is neither read nor updated.
*/
-unsigned long
-isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
- unsigned long low_pfn, unsigned long end_pfn, bool unevictable)
+static unsigned long
+isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
+ unsigned long end_pfn, isolate_mode_t isolate_mode)
{
- unsigned long last_pageblock_nr = 0, pageblock_nr;
+ struct zone *zone = cc->zone;
unsigned long nr_scanned = 0, nr_isolated = 0;
struct list_head *migratelist = &cc->migratepages;
struct lruvec *lruvec;
unsigned long flags;
bool locked = false;
struct page *page = NULL, *valid_page = NULL;
- bool set_unsuitable = true;
- const isolate_mode_t mode = (cc->mode == MIGRATE_ASYNC ?
- ISOLATE_ASYNC_MIGRATE : 0) |
- (unevictable ? ISOLATE_UNEVICTABLE : 0);
/*
* Ensure that there are not too many pages isolated from the LRU
@@ -515,19 +503,6 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
}
}
- /*
- * migrate_pfn does not necessarily start aligned to a
- * pageblock. Ensure that pfn_valid is called when moving
- * into a new MAX_ORDER_NR_PAGES range in case of large
- * memory holes within the zone
- */
- if ((low_pfn & (MAX_ORDER_NR_PAGES - 1)) == 0) {
- if (!pfn_valid(low_pfn)) {
- low_pfn += MAX_ORDER_NR_PAGES - 1;
- continue;
- }
- }
-
if (!pfn_valid_within(low_pfn))
continue;
nr_scanned++;
@@ -545,28 +520,6 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
if (!valid_page)
valid_page = page;
- /* If isolation recently failed, do not retry */
- pageblock_nr = low_pfn >> pageblock_order;
- if (last_pageblock_nr != pageblock_nr) {
- int mt;
-
- last_pageblock_nr = pageblock_nr;
- if (!isolation_suitable(cc, page))
- goto next_pageblock;
-
- /*
- * For async migration, also only scan in MOVABLE
- * blocks. Async migration is optimistic to see if
- * the minimum amount of work satisfies the allocation
- */
- mt = get_pageblock_migratetype(page);
- if (cc->mode == MIGRATE_ASYNC &&
- !migrate_async_suitable(mt)) {
- set_unsuitable = false;
- goto next_pageblock;
- }
- }
-
/*
* Skip if free. page_order cannot be used without zone->lock
* as nothing prevents parallel allocations or buddy merging.
@@ -601,8 +554,11 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
*/
if (PageTransHuge(page)) {
if (!locked)
- goto next_pageblock;
- low_pfn += (1 << compound_order(page)) - 1;
+ low_pfn = ALIGN(low_pfn + 1,
+ pageblock_nr_pages) - 1;
+ else
+ low_pfn += (1 << compound_order(page)) - 1;
+
continue;
}
@@ -632,7 +588,7 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
lruvec = mem_cgroup_page_lruvec(page, zone);
/* Try isolate the page */
- if (__isolate_lru_page(page, mode) != 0)
+ if (__isolate_lru_page(page, isolate_mode) != 0)
continue;
VM_BUG_ON_PAGE(PageTransCompound(page), page);
@@ -651,11 +607,6 @@ isolate_success:
++low_pfn;
break;
}
-
- continue;
-
-next_pageblock:
- low_pfn = ALIGN(low_pfn + 1, pageblock_nr_pages) - 1;
}
acct_isolated(zone, locked, cc);
@@ -668,8 +619,7 @@ next_pageblock:
* if the whole pageblock was scanned without isolating any page.
*/
if (low_pfn == end_pfn)
- update_pageblock_skip(cc, valid_page, nr_isolated,
- set_unsuitable, true);
+ update_pageblock_skip(cc, valid_page, nr_isolated, true);
trace_mm_compaction_isolate_migratepages(nr_scanned, nr_isolated);
@@ -680,15 +630,62 @@ next_pageblock:
return low_pfn;
}
+/**
+ * isolate_migratepages_range() - isolate migrate-able pages in a PFN range
+ * @cc: Compaction control structure.
+ * @start_pfn: The first PFN to start isolating.
+ * @end_pfn: The one-past-last PFN.
+ *
+ * Returns zero if isolation fails fatally due to e.g. pending signal.
+ * Otherwise, function returns one-past-the-last PFN of isolated page
+ * (which may be greater than end_pfn if end fell in a middle of a THP page).
+ */
+unsigned long
+isolate_migratepages_range(struct compact_control *cc, unsigned long start_pfn,
+ unsigned long end_pfn)
+{
+ unsigned long pfn, block_end_pfn;
+
+ /* Scan block by block. First and last block may be incomplete */
+ pfn = start_pfn;
+ block_end_pfn = ALIGN(pfn + 1, pageblock_nr_pages);
+
+ for (; pfn < end_pfn; pfn = block_end_pfn,
+ block_end_pfn += pageblock_nr_pages) {
+
+ block_end_pfn = min(block_end_pfn, end_pfn);
+
+ /* Skip whole pageblock in case of a memory hole */
+ if (!pfn_valid(pfn))
+ continue;
+
+ pfn = isolate_migratepages_block(cc, pfn, block_end_pfn,
+ ISOLATE_UNEVICTABLE);
+
+ /*
+ * In case of fatal failure, release everything that might
+ * have been isolated in the previous iteration, and signal
+ * the failure back to caller.
+ */
+ if (!pfn) {
+ putback_movable_pages(&cc->migratepages);
+ cc->nr_migratepages = 0;
+ break;
+ }
+ }
+
+ return pfn;
+}
+
#endif /* CONFIG_COMPACTION || CONFIG_CMA */
#ifdef CONFIG_COMPACTION
/*
* Based on information in the current compact_control, find blocks
* suitable for isolating free pages from and then isolate them.
*/
-static void isolate_freepages(struct zone *zone,
- struct compact_control *cc)
+static void isolate_freepages(struct compact_control *cc)
{
+ struct zone *zone = cc->zone;
struct page *page;
unsigned long block_start_pfn; /* start of current pageblock */
unsigned long block_end_pfn; /* end of current pageblock */
@@ -806,7 +803,7 @@ static struct page *compaction_alloc(struct page *migratepage,
*/
if (list_empty(&cc->freepages)) {
if (!cc->contended)
- isolate_freepages(cc->zone, cc);
+ isolate_freepages(cc);
if (list_empty(&cc->freepages))
return NULL;
@@ -840,34 +837,81 @@ typedef enum {
} isolate_migrate_t;
/*
- * Isolate all pages that can be migrated from the block pointed to by
- * the migrate scanner within compact_control.
+ * Isolate all pages that can be migrated from the first suitable block,
+ * starting at the block pointed to by the migrate scanner pfn within
+ * compact_control.
*/
static isolate_migrate_t isolate_migratepages(struct zone *zone,
struct compact_control *cc)
{
unsigned long low_pfn, end_pfn;
+ struct page *page;
+ const isolate_mode_t isolate_mode =
+ (cc->mode == MIGRATE_ASYNC ? ISOLATE_ASYNC_MIGRATE : 0);
- /* Do not scan outside zone boundaries */
- low_pfn = max(cc->migrate_pfn, zone->zone_start_pfn);
+ /*
+ * Start at where we last stopped, or beginning of the zone as
+ * initialized by compact_zone()
+ */
+ low_pfn = cc->migrate_pfn;
/* Only scan within a pageblock boundary */
end_pfn = ALIGN(low_pfn + 1, 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;
- }
+ /*
+ * Iterate over whole pageblocks until we find the first suitable.
+ * Do not cross the free scanner.
+ */
+ for (; end_pfn <= cc->free_pfn;
+ low_pfn = end_pfn, end_pfn += pageblock_nr_pages) {
+
+ /*
+ * This can potentially iterate a massively long zone with
+ * many pageblocks unsuitable, so periodically check if we
+ * need to schedule, or even abort async compaction.
+ */
+ if (!(low_pfn % (SWAP_CLUSTER_MAX * pageblock_nr_pages))
+ && compact_should_abort(cc))
+ break;
+
+ /* Skip whole pageblock in case of a memory hole */
+ if (!pfn_valid(low_pfn))
+ continue;
+
+ page = pfn_to_page(low_pfn);
+
+ /* If isolation recently failed, do not retry */
+ if (!isolation_suitable(cc, page))
+ continue;
+
+ /*
+ * For async compaction, also only scan in MOVABLE blocks.
+ * Async compaction is optimistic to see if the minimum amount
+ * of work satisfies the allocation.
+ */
+ if (cc->mode == MIGRATE_ASYNC &&
+ !migrate_async_suitable(get_pageblock_migratetype(page)))
+ continue;
+
+ /* Perform the isolation */
+ low_pfn = isolate_migratepages_block(cc, low_pfn, end_pfn,
+ isolate_mode);
+
+ if (!low_pfn || cc->contended)
+ return ISOLATE_ABORT;
- /* Perform the isolation */
- low_pfn = isolate_migratepages_range(zone, cc, low_pfn, end_pfn, false);
- if (!low_pfn || cc->contended)
- return ISOLATE_ABORT;
+ /*
+ * Either we isolated something and proceed with migration. Or
+ * we failed and compact_zone should decide if we should
+ * continue or not.
+ */
+ break;
+ }
+ /* Record where migration scanner will be restarted */
cc->migrate_pfn = low_pfn;
- return ISOLATE_SUCCESS;
+ return cc->nr_migratepages ? ISOLATE_SUCCESS : ISOLATE_NONE;
}
static int compact_finished(struct zone *zone,
@@ -1040,9 +1084,6 @@ static int compact_zone(struct zone *zone, struct compact_control *cc)
;
}
- if (!cc->nr_migratepages)
- continue;
-
err = migrate_pages(&cc->migratepages, compaction_alloc,
compaction_free, (unsigned long)cc, cc->mode,
MR_COMPACTION);
diff --git a/mm/internal.h b/mm/internal.h
index a1b651b..5a0738f 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -154,8 +154,8 @@ unsigned long
isolate_freepages_range(struct compact_control *cc,
unsigned long start_pfn, unsigned long end_pfn);
unsigned long
-isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
- unsigned long low_pfn, unsigned long end_pfn, bool unevictable);
+isolate_migratepages_range(struct compact_control *cc,
+ unsigned long low_pfn, unsigned long end_pfn);
#endif
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index f1586bc..5a1e0de 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6292,8 +6292,7 @@ static int __alloc_contig_migrate_range(struct compact_control *cc,
if (list_empty(&cc->migratepages)) {
cc->nr_migratepages = 0;
- pfn = isolate_migratepages_range(cc->zone, cc,
- pfn, end, true);
+ pfn = isolate_migratepages_range(cc, pfn, end);
if (!pfn) {
ret = -EINTR;
break;
--
1.8.4.5
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