Re: [PATCH V3] mm/vmstat: Add events for THP migration without split
From: John Hubbard
Date: Tue Jul 07 2020 - 20:01:47 EST
On 2020-07-06 17:06, Anshuman Khandual wrote:
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_FAILURE
3. THP_MIGRATION_SPLIT
In addition, these new events also update normal page migration statistics
appropriately via PGMIGRATE_SUCCESS and PGMIGRATE_FAILURE. While here, this
updates current trace event 'mm_migrate_pages' to accommodate now available
THP statistics.
Cc: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Zi Yan <ziy@xxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
This is missing the Documentation/ Cc's, did you run scripts/get_maintainer.pl? I'm
adding linux-doc and Jonathan Corbet, for now at least. And I'll refrain from
trimming the reply.
---
Changes in V3:
- 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 | 19 +++++++++++
include/linux/vm_event_item.h | 3 ++
include/trace/events/migrate.h | 17 ++++++++--
mm/migrate.c | 49 ++++++++++++++++++++++++++---
mm/vmstat.c | 3 ++
5 files changed, 84 insertions(+), 7 deletions(-)
diff --git a/Documentation/vm/page_migration.rst b/Documentation/vm/page_migration.rst
index 1d6cd7db4e43..e65d49f3cf86 100644
--- a/Documentation/vm/page_migration.rst
+++ b/Documentation/vm/page_migration.rst
@@ -253,5 +253,24 @@ 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.
+Quantifying Migration
+=====================
+Following events can be used to quantify page migration.
+
+1. PGMIGRATE_SUCCESS /* Normal page migration success */
This doesn't explain what's going on with the new combined counter
behavior. See the proposal below.
+2. PGMIGRATE_FAIL /* Normal page migration failure */
+3. THP_MIGRATION_SUCCESS /* Transparent huge page migration success */
+4. THP_MIGRATION_FAILURE /* Transparent huge page migration failure */
Shouldn't that be THP_MIGRATION_FAIL, in order to match the existing naming
scheme here?
+5. THP_MIGRATION_SPLIT /* Transparent huge page got split, retried */
+
+THP_MIGRATION_SUCCESS is when THP is migrated successfully without getting
+split into it's subpages. THP_MIGRATION_FAILURE is when THP could neither
+be migrated nor be split. THP_MIGRATION_SPLIT is when THP could not
+just be migrated as is but instead get split into it's subpages and later
+retried as normal pages. THP events would also update normal page migration
+statistics PGMIGRATE_SUCCESS and PGMIGRATE_FAILURE. These events will help
+in quantifying and analyzing various THP migration events including both
+success and failure cases.
+
I would like to propose the following instead of the above. It's rewritten
so as to add explanations for the new behavior, remove the redundancy (the last
sentence in particular is a justification, and belongs in a commit log if anywhere,
not in the doc itself), fix a few typos, use the full 80 columns, and clarify a
bit as well. It uses the new THP_MIGRATION_FAIL name:
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 at all, even after being
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 the sub-pages,
and that retry succeeded.
THP_MIGRATION_* events also update the appropriate PGMIGRATE_SUCCESS or
PGMIGRATE_FAILURE 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..5e7ffa025589 100644
--- a/include/linux/vm_event_item.h
+++ b/include/linux/vm_event_item.h
@@ -95,6 +95,9 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
THP_ZERO_PAGE_ALLOC_FAILED,
THP_SWPOUT,
THP_SWPOUT_FALLBACK,
+ THP_MIGRATION_SUCCESS,
+ THP_MIGRATION_FAILURE,
+ THP_MIGRATION_SPLIT,
#endif
#ifdef CONFIG_MEMORY_BALLOON
BALLOON_INFLATE,
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..baf3cc477d11 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, thp_nr_pages;
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);
+ thp_nr_pages = 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 += thp_nr_pages;
+ 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 += thp_nr_pages;
+ break;
+ }
nr_succeeded++;
break;
default:
@@ -1493,19 +1521,32 @@ 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 += thp_nr_pages;
+ 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);
+ if (nr_thp_succeeded)
+ count_vm_events(THP_MIGRATION_SUCCESS, nr_thp_succeeded);
+ if (nr_thp_failed)
+ count_vm_events(THP_MIGRATION_FAILURE, nr_thp_failed);
+ if (nr_thp_split)
+ count_vm_events(THP_MIGRATION_SPLIT, nr_thp_split);
As mentioned in the other thread, those "ifs" should be removed. I think you
can also get away with removing the two pre-existing "ifs" in the same
patch, too, just to keep the whole set consistent and more readable.
+ 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..a0fc7c86cdb7 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1280,6 +1280,9 @@ const char * const vmstat_text[] = {
"thp_zero_page_alloc_failed",
"thp_swpout",
"thp_swpout_fallback",
+ "thp_migration_success",
+ "thp_migration_failure",
+ "thp_migration_split",
#endif
#ifdef CONFIG_MEMORY_BALLOON
"balloon_inflate",
thanks,
--
John Hubbard
NVIDIA