!189 mm: page_alloc: Add a tracepoint to trace the call of __alloc_pages() and export symbols

Merge Pull Request from: @AoDaMo 
 
This is the result of the OSPP 2022 Project

/proc/meminfo is the main way for user to know the physical memory usage, but it cannot know every operation of allocating physical pages. Some kernel modules can call alloc_pages to get physical pages directly, which part of physical memory will not be counted by /proc/meminfo.
    
In order to trace the specific process of physical page allocation and release, a solution is to insert a new modules into kernel and register tracepoint handlers to obtain the physical page allocation information. So i added a new tracepoint named mm_page_alloc_enter at the entrance of mm/page_alloc.c:__alloc_pages(), and exported relevant tracepoint symbols for kernel module programming. 
 
Link:https://gitee.com/openeuler/kernel/pulls/189 
Reviewed-by: Liu YongQiang <liuyongqiang13@huawei.com> 
Reviewed-by: Zheng Zengkai <zhengzengkai@huawei.com> 
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com> 

Documentation/trace/events-kmem.rst

@@ -47,13 +47,15 @@ but the call_site can usually be used to extrapolate that information.
 ::
 
   mm_page_alloc		  page=%p pfn=%lu order=%d migratetype=%d gfp_flags=%s
+  mm_page_alloc_enter		  order=%d gfp_flags=%s
   mm_page_alloc_zone_locked page=%p pfn=%lu order=%u migratetype=%d cpu=%d percpu_refill=%d
   mm_page_free		  page=%p pfn=%lu order=%d
   mm_page_free_batched	  page=%p pfn=%lu order=%d cold=%d
 
-These four events deal with page allocation and freeing. mm_page_alloc is
-a simple indicator of page allocator activity. Pages may be allocated from
-the per-CPU allocator (high performance) or the buddy allocator.
+These five events deal with page allocation and freeing. mm_page_alloc_enter
+is the entry point of page allocation and can be used to analyze the time cost
+of page allocation. mm_page_alloc is a simple indicator of page allocator activity.
+Pages may be allocated from the per-CPU allocator (high performance) or the buddy allocator.
 
 If pages are allocated directly from the buddy allocator, the
 mm_page_alloc_zone_locked event is triggered. This event is important as high

include/trace/events/kmem.h

@@ -190,6 +190,26 @@ TRACE_EVENT(mm_page_free_batched,
 			__entry->pfn)
 );
 
+TRACE_EVENT(mm_page_alloc_enter,
+	TP_PROTO(unsigned int order, gfp_t gfp_flags),
+
+	TP_ARGS(order, gfp_flags),
+
+	TP_STRUCT__entry(
+		__field(	unsigned int,	order	)
+		__field(	gfp_t,		gfp_flags	)
+	),
+
+	TP_fast_assign(
+		__entry->order		= order;
+		__entry->gfp_flags	= gfp_flags;
+	),
+
+	TP_printk("order=%d gfp_flags=%s",
+		__entry->order,
+		show_gfp_flags(__entry->gfp_flags))
+);
+
 TRACE_EVENT(mm_page_alloc,
 
 	TP_PROTO(struct page *page, unsigned int order,

mm/page_alloc.c

@@ -82,6 +82,12 @@
 #include "shuffle.h"
 #include "page_reporting.h"
 
+EXPORT_TRACEPOINT_SYMBOL_GPL(mm_page_alloc_enter);
+EXPORT_TRACEPOINT_SYMBOL_GPL(mm_page_alloc);
+EXPORT_TRACEPOINT_SYMBOL_GPL(mm_page_alloc_zone_locked);
+EXPORT_TRACEPOINT_SYMBOL_GPL(mm_page_free);
+EXPORT_TRACEPOINT_SYMBOL_GPL(mm_page_free_batched);
+
 /* Free Page Internal flags: for internal, non-pcp variants of free_pages(). */
 typedef int __bitwise fpi_t;
 
@@ -5291,6 +5297,8 @@ struct page *__alloc_pages(gfp_t gfp, unsigned int order, int preferred_nid,
 	gfp_t alloc_gfp; /* The gfp_t that was actually used for allocation */
 	struct alloc_context ac = { };
 
+	trace_mm_page_alloc_enter(order, gfp);
+
 	/*
 	 * There are several places where we assume that the order value is sane
 	 * so bail out early if the request is out of bound.