[PATCH] mm/migration: Add trace events for THP migrations

[Anshuman Khandual <anshuman.khandual@arm.com>]

This adds two trace events for PMD based THP migration without split. These
events closely follow the implementation details like setting and removing
of PMD migration entries, which are essential operations for THP migration.

Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
---
This applies on v5.16-rc8

Changes in V1:

- Dropped mm, pmdp, page arguments from trace
- Updated trace argument names and output format

Changes in RFC:

https://lore.kernel.org/all/1640328398-20698-1-git-send-email-anshuman.khandual@arm.com/

 include/trace/events/thp.h | 37 +++++++++++++++++++++++++++++++++++++
 mm/huge_memory.c           |  5 +++++
 2 files changed, 42 insertions(+)

diff --git a/include/trace/events/thp.h b/include/trace/events/thp.h
index d7fbbe551841..193a555aa2ea 100644
--- a/include/trace/events/thp.h
+++ b/include/trace/events/thp.h
@@ -83,6 +83,43 @@ TRACE_EVENT(hugepage_splitting,
 		      __entry->addr, __entry->pte)
 );
 
+TRACE_EVENT(set_migration_pmd,
+
+	TP_PROTO(unsigned long addr, unsigned long pmd),
+
+	TP_ARGS(addr, pmd),
+
+	TP_STRUCT__entry(
+		__field(unsigned long, addr)
+		__field(unsigned long, pmd)
+	),
+
+	TP_fast_assign(
+		__entry->addr = addr;
+		__entry->pmd = pmd;
+	),
+
+	TP_printk("create pmd migration entry addr=%lx, pmd=%lx", __entry->addr, __entry->pmd)
+);
+
+TRACE_EVENT(remove_migration_pmd,
+
+	TP_PROTO(unsigned long addr, unsigned long pmd),
+
+	TP_ARGS(addr, pmd),
+
+	TP_STRUCT__entry(
+		__field(unsigned long, addr)
+		__field(unsigned long, pmd)
+	),
+
+	TP_fast_assign(
+		__entry->addr = addr;
+		__entry->pmd = pmd;
+	),
+
+	TP_printk("remove pmd migration entry addr=%lx, val=%lx", __entry->addr, __entry->pmd)
+);
 #endif /* _TRACE_THP_H */
 
 /* This part must be outside protection */
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index e5483347291c..d0adc019afe0 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -39,6 +39,9 @@
 #include <asm/pgalloc.h>
 #include "internal.h"
 
+#define CREATE_TRACE_POINTS
+#include <trace/events/thp.h>
+
 /*
  * By default, transparent hugepage support is disabled in order to avoid
  * risking an increased memory footprint for applications that are not
@@ -3173,6 +3176,7 @@ void set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw,
 	set_pmd_at(mm, address, pvmw->pmd, pmdswp);
 	page_remove_rmap(page, true);
 	put_page(page);
+	trace_set_migration_pmd(address, pmd_val(pmdswp));
 }
 
 void remove_migration_pmd(struct page_vma_mapped_walk *pvmw, struct page *new)
@@ -3206,5 +3210,6 @@ void remove_migration_pmd(struct page_vma_mapped_walk *pvmw, struct page *new)
 	if ((vma->vm_flags & VM_LOCKED) && !PageDoubleMap(new))
 		mlock_vma_page(new);
 	update_mmu_cache_pmd(vma, address, pvmw->pmd);
+	trace_remove_migration_pmd(address, pmd_val(pmde));
 }
 #endif
-- 
2.20.1