Message-Id: <1594287583-16568-1-git-send-email-anshuman.khandual@arm.com>
Date:   Thu,  9 Jul 2020 15:09:43 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     linux-mm@...ck.org
Cc:     Anshuman Khandual <anshuman.khandual@....com>,
        Jonathan Corbet <corbet@....net>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        Hugh Dickins <hughd@...gle.com>,
        Matthew Wilcox <willy@...radead.org>, Zi Yan <ziy@...dia.com>,
        John Hubbard <jhubbard@...dia.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH V4] mm/vmstat: Add events for THP migration without split

Add following new vmstat events which will help in validating THP migration
without split. Statistics reported through these new VM events will help in
performance debugging.

1. THP_MIGRATION_SUCCESS
2. THP_MIGRATION_FAIL
3. THP_MIGRATION_SPLIT

In addition, these new events also update normal page migration statistics
appropriately via PGMIGRATE_SUCCESS and PGMIGRATE_FAIL. While here, this
updates current trace event 'mm_migrate_pages' to accommodate now available
THP statistics.

Cc: Jonathan Corbet <corbet@....net>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Daniel Jordan <daniel.m.jordan@...cle.com>
Cc: Hugh Dickins <hughd@...gle.com>
Cc: Matthew Wilcox <willy@...radead.org>
Cc: Zi Yan <ziy@...dia.com>
Cc: John Hubbard <jhubbard@...dia.com>
Cc: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-doc@...r.kernel.org
Cc: linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org
Signed-off-by: Zi Yan <ziy@...dia.com>
Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
---
Applies on 5.8-rc4.

Changes in V4:

- Changed THP_MIGRATION_FAILURE as THP_MIGRATION_FAIL per John
- Dropped all conditional 'if' blocks in migrate_pages() per Andrew and John
- Updated migration events documentation per John
- Updated thp_nr_pages variable as nr_subpages for an expected merge conflict
- Moved all new THP vmstat events into CONFIG_MIGRATION
- Updated Cc list with Documentation/ and tracing related addresses

Changes in V3: (https://patchwork.kernel.org/patch/11647237/)

- Formatted new events documentation with 'fmt' tool per Matthew
- Made events universally available i.e dropped ARCH_ENABLE_THP_MIGRATION
- Added THP_MIGRATION_SPLIT
- Updated trace_mm_migrate_pages() with THP events
- Made THP events update normal page migration events as well

Changes in V2: (https://patchwork.kernel.org/patch/11586893/)

- Dropped PMD reference both from code and commit message per Matthew
- Added documentation and updated the commit message per Daniel

Changes in V1: (https://patchwork.kernel.org/patch/11564497/)

- Changed function name as thp_pmd_migration_success() per John
- Folded in a fix (https://patchwork.kernel.org/patch/11563009/) from Hugh

Changes in RFC V2: (https://patchwork.kernel.org/patch/11554861/)

- Decopupled and renamed VM events from their implementation per Zi and John
- Added THP_PMD_MIGRATION_FAILURE VM event upon allocation failure and split

Changes in RFC V1: (https://patchwork.kernel.org/patch/11542055/)

 Documentation/vm/page_migration.rst | 27 +++++++++++++++
 include/linux/vm_event_item.h       |  3 ++
 include/trace/events/migrate.h      | 17 ++++++++--
 mm/migrate.c                        | 52 ++++++++++++++++++++++++-----
 mm/vmstat.c                         |  3 ++
 5 files changed, 91 insertions(+), 11 deletions(-)

diff --git a/Documentation/vm/page_migration.rst b/Documentation/vm/page_migration.rst
index 1d6cd7db4e43..68883ac485fa 100644
--- a/Documentation/vm/page_migration.rst
+++ b/Documentation/vm/page_migration.rst
@@ -253,5 +253,32 @@ which are function pointers of struct address_space_operations.
      PG_isolated is alias with PG_reclaim flag so driver shouldn't use the flag
      for own purpose.
 
+Monitoring Migration
+=====================
+
+The following events (counters) can be used to monitor page migration.
+
+1. PGMIGRATE_SUCCESS: Normal page migration success. Each count means that a
+   page was migrated. If the page was a non-THP page, then this counter is
+   increased by one. If the page was a THP, then this counter is increased by
+   the number of THP subpages. For example, migration of a single 2MB THP that
+   has 4KB-size base pages (subpages) will cause this counter to increase by
+   512.
+
+2. PGMIGRATE_FAIL: Normal page migration failure. Same counting rules as for
+   _SUCCESS, above: this will be increased by the number of subpages, if it was
+   a THP.
+
+3. THP_MIGRATION_SUCCESS: A THP was migrated without being split.
+
+4. THP_MIGRATION_FAIL: A THP could not be migrated nor it could be split.
+
+5. THP_MIGRATION_SPLIT: A THP was migrated, but not as such: first, the THP had
+   to be split. After splitting, a migration retry was used for it's sub-pages.
+
+THP_MIGRATION_* events also update the appropriate PGMIGRATE_SUCCESS or
+PGMIGRATE_FAIL events. For example, a THP migration failure will cause both
+THP_MIGRATION_FAIL and PGMIGRATE_FAIL to increase.
+
 Christoph Lameter, May 8, 2006.
 Minchan Kim, Mar 28, 2016.
diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
index 24fc7c3ae7d6..2e6ca53b9bbd 100644
--- a/include/linux/vm_event_item.h
+++ b/include/linux/vm_event_item.h
@@ -56,6 +56,9 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
 #endif
 #ifdef CONFIG_MIGRATION
 		PGMIGRATE_SUCCESS, PGMIGRATE_FAIL,
+		THP_MIGRATION_SUCCESS,
+		THP_MIGRATION_FAIL,
+		THP_MIGRATION_SPLIT,
 #endif
 #ifdef CONFIG_COMPACTION
 		COMPACTMIGRATE_SCANNED, COMPACTFREE_SCANNED,
diff --git a/include/trace/events/migrate.h b/include/trace/events/migrate.h
index 705b33d1e395..4d434398d64d 100644
--- a/include/trace/events/migrate.h
+++ b/include/trace/events/migrate.h
@@ -46,13 +46,18 @@ MIGRATE_REASON
 TRACE_EVENT(mm_migrate_pages,
 
 	TP_PROTO(unsigned long succeeded, unsigned long failed,
-		 enum migrate_mode mode, int reason),
+		 unsigned long thp_succeeded, unsigned long thp_failed,
+		 unsigned long thp_split, enum migrate_mode mode, int reason),
 
-	TP_ARGS(succeeded, failed, mode, reason),
+	TP_ARGS(succeeded, failed, thp_succeeded, thp_failed,
+		thp_split, mode, reason),
 
 	TP_STRUCT__entry(
 		__field(	unsigned long,		succeeded)
 		__field(	unsigned long,		failed)
+		__field(	unsigned long,		thp_succeeded)
+		__field(	unsigned long,		thp_failed)
+		__field(	unsigned long,		thp_split)
 		__field(	enum migrate_mode,	mode)
 		__field(	int,			reason)
 	),
@@ -60,13 +65,19 @@ TRACE_EVENT(mm_migrate_pages,
 	TP_fast_assign(
 		__entry->succeeded	= succeeded;
 		__entry->failed		= failed;
+		__entry->thp_succeeded	= thp_succeeded;
+		__entry->thp_failed	= thp_failed;
+		__entry->thp_split	= thp_split;
 		__entry->mode		= mode;
 		__entry->reason		= reason;
 	),
 
-	TP_printk("nr_succeeded=%lu nr_failed=%lu mode=%s reason=%s",
+	TP_printk("nr_succeeded=%lu nr_failed=%lu nr_thp_succeeded=%lu nr_thp_failed=%lu nr_thp_split=%lu mode=%s reason=%s",
 		__entry->succeeded,
 		__entry->failed,
+		__entry->thp_succeeded,
+		__entry->thp_failed,
+		__entry->thp_split,
 		__print_symbolic(__entry->mode, MIGRATE_MODE),
 		__print_symbolic(__entry->reason, MIGRATE_REASON))
 );
diff --git a/mm/migrate.c b/mm/migrate.c
index f37729673558..c706e3576cfc 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1429,22 +1429,35 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
 		enum migrate_mode mode, int reason)
 {
 	int retry = 1;
+	int thp_retry = 1;
 	int nr_failed = 0;
 	int nr_succeeded = 0;
+	int nr_thp_succeeded = 0;
+	int nr_thp_failed = 0;
+	int nr_thp_split = 0;
 	int pass = 0;
+	bool is_thp = false;
 	struct page *page;
 	struct page *page2;
 	int swapwrite = current->flags & PF_SWAPWRITE;
-	int rc;
+	int rc, nr_subpages;
 
 	if (!swapwrite)
 		current->flags |= PF_SWAPWRITE;
 
-	for(pass = 0; pass < 10 && retry; pass++) {
+	for (pass = 0; pass < 10 && (retry || thp_retry); pass++) {
 		retry = 0;
+		thp_retry = 0;
 
 		list_for_each_entry_safe(page, page2, from, lru) {
 retry:
+			/*
+			 * THP statistics is based on the source huge page.
+			 * Capture required information that might get lost
+			 * during migration.
+			 */
+			is_thp = PageTransHuge(page);
+			nr_subpages = hpage_nr_pages(page);
 			cond_resched();
 
 			if (PageHuge(page))
@@ -1475,15 +1488,30 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
 					unlock_page(page);
 					if (!rc) {
 						list_safe_reset_next(page, page2, lru);
+						nr_thp_split++;
 						goto retry;
 					}
 				}
+				if (is_thp) {
+					nr_thp_failed++;
+					nr_failed += nr_subpages;
+					goto out;
+				}
 				nr_failed++;
 				goto out;
 			case -EAGAIN:
+				if (is_thp) {
+					thp_retry++;
+					break;
+				}
 				retry++;
 				break;
 			case MIGRATEPAGE_SUCCESS:
+				if (is_thp) {
+					nr_thp_succeeded++;
+					nr_succeeded += nr_subpages;
+					break;
+				}
 				nr_succeeded++;
 				break;
 			default:
@@ -1493,19 +1521,27 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
 				 * removed from migration page list and not
 				 * retried in the next outer loop.
 				 */
+				if (is_thp) {
+					nr_thp_failed++;
+					nr_failed += nr_subpages;
+					break;
+				}
 				nr_failed++;
 				break;
 			}
 		}
 	}
-	nr_failed += retry;
+	nr_failed += retry + thp_retry;
+	nr_thp_failed += thp_retry;
 	rc = nr_failed;
 out:
-	if (nr_succeeded)
-		count_vm_events(PGMIGRATE_SUCCESS, nr_succeeded);
-	if (nr_failed)
-		count_vm_events(PGMIGRATE_FAIL, nr_failed);
-	trace_mm_migrate_pages(nr_succeeded, nr_failed, mode, reason);
+	count_vm_events(PGMIGRATE_SUCCESS, nr_succeeded);
+	count_vm_events(PGMIGRATE_FAIL, nr_failed);
+	count_vm_events(THP_MIGRATION_SUCCESS, nr_thp_succeeded);
+	count_vm_events(THP_MIGRATION_FAIL, nr_thp_failed);
+	count_vm_events(THP_MIGRATION_SPLIT, nr_thp_split);
+	trace_mm_migrate_pages(nr_succeeded, nr_failed, nr_thp_succeeded,
+			       nr_thp_failed, nr_thp_split, mode, reason);
 
 	if (!swapwrite)
 		current->flags &= ~PF_SWAPWRITE;
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 3fb23a21f6dd..09914a4bfee4 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1234,6 +1234,9 @@ const char * const vmstat_text[] = {
 #ifdef CONFIG_MIGRATION
 	"pgmigrate_success",
 	"pgmigrate_fail",
+	"thp_migration_success",
+	"thp_migration_fail",
+	"thp_migration_split",
 #endif
 #ifdef CONFIG_COMPACTION
 	"compact_migrate_scanned",
-- 
2.20.1

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