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

[Anshuman Khandual]

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@xxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Zi Yan <ziy@xxxxxxxxxx>
Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
---
This applies on v5.16-rc6

 include/trace/events/thp.h | 61 ++++++++++++++++++++++++++++++++++++++
 mm/huge_memory.c           |  5 ++++
 2 files changed, 66 insertions(+)

diff --git a/include/trace/events/thp.h b/include/trace/events/thp.h
index d7fbbe551841..be5aeb783af1 100644
--- a/include/trace/events/thp.h
+++ b/include/trace/events/thp.h
@@ -83,6 +83,67 @@ TRACE_EVENT(hugepage_splitting,
 		      __entry->addr, __entry->pte)
 );
 
+TRACE_EVENT(set_migration_pmd,
+
+	TP_PROTO(struct mm_struct *mm, unsigned long address,
+		 pmd_t *pmdp, struct page *page, unsigned long pmdval),
+
+	TP_ARGS(mm, address, pmdp, page, pmdval),
+
+	TP_STRUCT__entry(
+		__field(struct mm_struct *, mm)
+		__field(unsigned long, address)
+		__field(pmd_t *, pmdp)
+		__field(struct page *, page)
+		__field(unsigned long, pmdval)
+	),
+
+	TP_fast_assign(
+		__entry->mm = mm;
+		__entry->address = address;
+		__entry->pmdp = pmdp;
+		__entry->page = page;
+		__entry->pmdval = pmdval;
+	),
+
+	TP_printk("mm=%p, address=%lx, pmdp=%p, page=%p pmdval=%lx",
+		__entry->mm,
+		__entry->address,
+		__entry->pmdp,
+		__entry->page,
+		__entry->pmdval)
+);
+
+TRACE_EVENT(remove_migration_pmd,
+
+	TP_PROTO(struct mm_struct *mm, unsigned long address,
+		 pmd_t *pmdp, struct page *page, unsigned long pmdval),
+
+	TP_ARGS(mm, address, pmdp, page, pmdval),
+
+	TP_STRUCT__entry(
+		__field(struct mm_struct *, mm)
+		__field(unsigned long, address)
+		__field(pmd_t *, pmdp)
+		__field(struct page *, page)
+		__field(unsigned long, pmdval)
+	),
+
+	TP_fast_assign(
+		__entry->mm = mm;
+		__entry->address = address;
+		__entry->pmdp = pmdp;
+		__entry->page = page;
+		__entry->pmdval = pmdval;
+	),
+
+	TP_printk("mm=%p, address=%lx, pmdp=%p, page=%p pmdval=%lx",
+		__entry->mm,
+		__entry->address,
+		__entry->pmdp,
+		__entry->page,
+		__entry->pmdval)
+);
 #endif /* _TRACE_THP_H */
 
 /* This part must be outside protection */
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index e5483347291c..611de486e095 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(mm, address, pvmw->pmd, page, 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(mm, address, pvmw->pmd, new, pmd_val(pmde));
 }
 #endif
-- 
2.20.1