On 05/01/2014 11:35 PM, David Rientjes wrote:
Each zone has a cached migration scanner pfn for memory compaction so that
subsequent calls to memory compaction can start where the previous call left
off.
Currently, the compaction migration scanner only updates the per-zone cached pfn
when pageblocks were not skipped for async compaction. This creates a
dependency on calling sync compaction to avoid having subsequent calls to async
compaction from scanning an enormous amount of non-MOVABLE pageblocks each time
it is called. On large machines, this could be potentially very expensive.
OK that's due to my commit 50b5b094e6 ("mm: compaction: do not mark
unmovable pageblocks as skipped in async compaction") and the intention
was to avoid marking pageblocks as to-be-skipped just because they were
ignored by async compaction, which would make the following sync
compaction ignore them as well. However it's true that
update_pageblock_skip() also updates the cached pfn's and not updating
them is a sideeffect of this change.
I didn't think that would be a problem as skipping whole pageblocks due
to being non-movable should be fast and without taking locks. But if
your testing shows that this is a problem, then OK.
This patch adds a per-zone cached migration scanner pfn only for async
compaction. It is updated everytime a pageblock has been scanned in its
entirety and when no pages from it were successfully isolated. The cached
migration scanner pfn for sync compaction is updated only when called for sync
compaction.
I think this might be an overkill and maybe just decoupling the cached
pfn update from the update_pageblock_skip() would be enough, i.e.
restore pre-50b5b094e6 behavior for the cached pfn (but not for the skip
bits)? I wonder if your new sync migration scanner would make any
difference. Presumably when async compaction finishes without success by
having the scanners meet, compact_finished() will reset the cached pfn's
and the sync compaction will not have a chance to use any previously
cached value anyway?
Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
---
include/linux/mmzone.h | 5 +++--
mm/compaction.c | 55 ++++++++++++++++++++++++++------------------------
2 files changed, 32 insertions(+), 28 deletions(-)
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -360,9 +360,10 @@ struct zone {
/* Set to true when the PG_migrate_skip bits should be cleared */
bool compact_blockskip_flush;
- /* pfns where compaction scanners should start */
+ /* pfn where compaction free scanner should start */
unsigned long compact_cached_free_pfn;
- unsigned long compact_cached_migrate_pfn;
+ /* pfn where async and sync compaction migration scanner should start */
+ unsigned long compact_cached_migrate_pfn[2];
#endif
#ifdef CONFIG_MEMORY_HOTPLUG
/* see spanned/present_pages for more description */
diff --git a/mm/compaction.c b/mm/compaction.c
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -89,7 +89,8 @@ static void __reset_isolation_suitable(struct zone *zone)
unsigned long end_pfn = zone_end_pfn(zone);
unsigned long pfn;
- zone->compact_cached_migrate_pfn = start_pfn;
+ zone->compact_cached_migrate_pfn[0] = start_pfn;
+ zone->compact_cached_migrate_pfn[1] = start_pfn;
zone->compact_cached_free_pfn = end_pfn;
zone->compact_blockskip_flush = false;
@@ -134,6 +135,7 @@ static void update_pageblock_skip(struct compact_control *cc,
bool migrate_scanner)
{
struct zone *zone = cc->zone;
+ unsigned long pfn;
if (cc->ignore_skip_hint)
return;
@@ -141,20 +143,25 @@ static void update_pageblock_skip(struct compact_control *cc,
if (!page)
return;
- if (!nr_isolated) {
- unsigned long pfn = page_to_pfn(page);
- set_pageblock_skip(page);
-
- /* Update where compaction should restart */
- if (migrate_scanner) {
- if (!cc->finished_update_migrate &&
- pfn > zone->compact_cached_migrate_pfn)
- zone->compact_cached_migrate_pfn = pfn;
- } else {
- if (!cc->finished_update_free &&
- pfn < zone->compact_cached_free_pfn)
- zone->compact_cached_free_pfn = pfn;
- }
+ if (nr_isolated)
+ return;
+
+ set_pageblock_skip(page);
+ pfn = page_to_pfn(page);
+
+ /* Update where async and sync compaction should restart */
+ if (migrate_scanner) {
+ if (cc->finished_update_migrate)
+ return;
+ if (pfn > zone->compact_cached_migrate_pfn[0])
+ zone->compact_cached_migrate_pfn[0] = pfn;
+ if (cc->sync && pfn > zone->compact_cached_migrate_pfn[1])
+ zone->compact_cached_migrate_pfn[1] = pfn;
+ } else {
+ if (cc->finished_update_free)
+ return;
+ if (pfn < zone->compact_cached_free_pfn)
+ zone->compact_cached_free_pfn = pfn;
}
}
#else
@@ -464,7 +471,6 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
unsigned long flags;
bool locked = false;
struct page *page = NULL, *valid_page = NULL;
- bool skipped_async_unsuitable = false;
const isolate_mode_t mode = (!cc->sync ? ISOLATE_ASYNC_MIGRATE : 0) |
(unevictable ? ISOLATE_UNEVICTABLE : 0);
@@ -540,11 +546,8 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
* the minimum amount of work satisfies the allocation
*/
mt = get_pageblock_migratetype(page);
- if (!cc->sync && !migrate_async_suitable(mt)) {
- cc->finished_update_migrate = true;
- skipped_async_unsuitable = true;
+ if (!cc->sync && !migrate_async_suitable(mt))
goto next_pageblock;
- }
}
/*
@@ -646,10 +649,8 @@ next_pageblock:
/*
* Update the pageblock-skip information and cached scanner pfn,
* if the whole pageblock was scanned without isolating any page.
- * This is not done when pageblock was skipped due to being unsuitable
- * for async compaction, so that eventual sync compaction can try.
*/
- if (low_pfn == end_pfn && !skipped_async_unsuitable)
+ if (low_pfn == end_pfn)
update_pageblock_skip(cc, valid_page, nr_isolated, true);
trace_mm_compaction_isolate_migratepages(nr_scanned, nr_isolated);
@@ -875,7 +876,8 @@ static int compact_finished(struct zone *zone,
/* Compaction run completes if the migrate and free scanner meet */
if (cc->free_pfn <= cc->migrate_pfn) {
/* Let the next compaction start anew. */
- zone->compact_cached_migrate_pfn = zone->zone_start_pfn;
+ zone->compact_cached_migrate_pfn[0] = zone->zone_start_pfn;
+ zone->compact_cached_migrate_pfn[1] = zone->zone_start_pfn;
zone->compact_cached_free_pfn = zone_end_pfn(zone);
/*
@@ -1000,7 +1002,7 @@ static int compact_zone(struct zone *zone, struct compact_control *cc)
* information on where the scanners should start but check that it
* is initialised by ensuring the values are within zone boundaries.
*/
- cc->migrate_pfn = zone->compact_cached_migrate_pfn;
+ cc->migrate_pfn = zone->compact_cached_migrate_pfn[cc->sync];
cc->free_pfn = zone->compact_cached_free_pfn;
if (cc->free_pfn < start_pfn || cc->free_pfn > end_pfn) {
cc->free_pfn = end_pfn & ~(pageblock_nr_pages-1);
@@ -1008,7 +1010,8 @@ static int compact_zone(struct zone *zone, struct compact_control *cc)
}
if (cc->migrate_pfn < start_pfn || cc->migrate_pfn > end_pfn) {
cc->migrate_pfn = start_pfn;
- zone->compact_cached_migrate_pfn = cc->migrate_pfn;
+ zone->compact_cached_migrate_pfn[0] = cc->migrate_pfn;
+ zone->compact_cached_migrate_pfn[1] = cc->migrate_pfn;
}
trace_mm_compaction_begin(start_pfn, cc->migrate_pfn, cc->free_pfn, end_pfn);
--
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