Commit 95813b8f authored by Joonsoo Kim's avatar Joonsoo Kim Committed by Linus Torvalds
Browse files

mm/page_ref: add tracepoint to track down page reference manipulation 

CMA allocation should be guaranteed to succeed by definition, but,
unfortunately, it would be failed sometimes.  It is hard to track down
the problem, because it is related to page reference manipulation and we
don't have any facility to analyze it.

This patch adds tracepoints to track down page reference manipulation.
With it, we can find exact reason of failure and can fix the problem.
Following is an example of tracepoint output.  (note: this example is
stale version that printing flags as the number.  Recent version will
print it as human readable string.)

<...>-9018  [004]    92.678375: page_ref_set:         pfn=0x17ac9 flags=0x0 count=1 mapcount=0 mapping=(nil) mt=4 val=1
<...>-9018  [004]    92.678378: kernel_stack:
 => get_page_from_freelist (ffffffff81176659)
 => __alloc_pages_nodemask (ffffffff81176d22)
 => alloc_pages_vma (ffffffff811bf675)
 => handle_mm_fault (ffffffff8119e693)
 => __do_page_fault (ffffffff810631ea)
 => trace_do_page_fault (ffffffff81063543)
 => do_async_page_fault (ffffffff8105c40a)
 => async_page_fault (ffffffff817581d8)
[snip]
<...>-9018  [004]    92.678379: page_ref_mod:         pfn=0x17ac9 flags=0x40048 count=2 mapcount=1 mapping=0xffff880015a78dc1 mt=4 val=1
[snip]
...
...
<...>-9131  [001]    93.174468: test_pages_isolated:  start_pfn=0x17800 end_pfn=0x17c00 fin_pfn=0x17ac9 ret=fail
[snip]
<...>-9018  [004]    93.174843: page_ref_mod_and_test: pfn=0x17ac9 flags=0x40068 count=0 mapcount=0 mapping=0xffff880015a78dc1 mt=4 val=-1 ret=1
 => release_pages (ffffffff8117c9e4)
 => free_pages_and_swap_cache (ffffffff811b0697)
 => tlb_flush_mmu_free (ffffffff81199616)
 => tlb_finish_mmu (ffffffff8119a62c)
 => exit_mmap (ffffffff811a53f7)
 => mmput (ffffffff81073f47)
 => do_exit (ffffffff810794e9)
 => do_group_exit (ffffffff81079def)
 => SyS_exit_group (ffffffff81079e74)
 => entry_SYSCALL_64_fastpath (ffffffff817560b6)

This output shows that problem comes from exit path.  In exit path, to
improve performance, pages are not freed immediately.  They are gathered
and processed by batch.  During this process, migration cannot be
possible and CMA allocation is failed.  This problem is hard to find
without this page reference tracepoint facility.

Enabling this feature bloat kernel text 30 KB in my configuration.

   text    data     bss     dec     hex filename
12127327        2243616 1507328 15878271         f2487f vmlinux_disabled
12157208        2258880 1507328 15923416         f2f8d8 vmlinux_enabled

Note that, due to header file dependency problem between mm.h and
tracepoint.h, this feature has to open code the static key functions for
tracepoints.  Proposed by Steven Rostedt in following link.

https://lkml.org/lkml/2015/12/9/699



[arnd@arndb.de: crypto/async_pq: use __free_page() instead of put_page()]
[iamjoonsoo.kim@lge.com: fix build failure for xtensa]
[akpm@linux-foundation.org: tweak Kconfig text, per Vlastimil]
Signed-off-by: default avatarJoonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: default avatarMichal Nazarewicz <mina86@mina86.com>
Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Acked-by: default avatarSteven Rostedt <rostedt@goodmis.org>
Signed-off-by: default avatarArnd Bergmann <arnd@arndb.de>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent fe896d18

crypto/async_tx/async_pq.c

+1 −1
Original line number Diff line number Diff line
@@ -444,7 +444,7 @@ static int __init async_pq_init(void) 


static void __exit async_pq_exit(void)

{

	put_page(pq_scribble_page);

	__free_page(pq_scribble_page);

}



module_init(async_pq_init);

include/linux/page_ref.h

+93 −5
Original line number Diff line number Diff line
@@ -4,6 +4,62 @@ 
#include <linux/atomic.h>

#include <linux/mm_types.h>

#include <linux/page-flags.h>

#include <linux/tracepoint-defs.h>



extern struct tracepoint __tracepoint_page_ref_set;

extern struct tracepoint __tracepoint_page_ref_mod;

extern struct tracepoint __tracepoint_page_ref_mod_and_test;

extern struct tracepoint __tracepoint_page_ref_mod_and_return;

extern struct tracepoint __tracepoint_page_ref_mod_unless;

extern struct tracepoint __tracepoint_page_ref_freeze;

extern struct tracepoint __tracepoint_page_ref_unfreeze;



#ifdef CONFIG_DEBUG_PAGE_REF



/*

 * Ideally we would want to use the trace_<tracepoint>_enabled() helper

 * functions. But due to include header file issues, that is not

 * feasible. Instead we have to open code the static key functions.

 *

 * See trace_##name##_enabled(void) in include/linux/tracepoint.h

 */

#define page_ref_tracepoint_active(t) static_key_false(&(t).key)



extern void __page_ref_set(struct page *page, int v);

extern void __page_ref_mod(struct page *page, int v);

extern void __page_ref_mod_and_test(struct page *page, int v, int ret);

extern void __page_ref_mod_and_return(struct page *page, int v, int ret);

extern void __page_ref_mod_unless(struct page *page, int v, int u);

extern void __page_ref_freeze(struct page *page, int v, int ret);

extern void __page_ref_unfreeze(struct page *page, int v);



#else



#define page_ref_tracepoint_active(t) false



static inline void __page_ref_set(struct page *page, int v)

{

}

static inline void __page_ref_mod(struct page *page, int v)

{

}

static inline void __page_ref_mod_and_test(struct page *page, int v, int ret)

{

}

static inline void __page_ref_mod_and_return(struct page *page, int v, int ret)

{

}

static inline void __page_ref_mod_unless(struct page *page, int v, int u)

{

}

static inline void __page_ref_freeze(struct page *page, int v, int ret)

{

}

static inline void __page_ref_unfreeze(struct page *page, int v)

{

}



#endif



static inline int page_ref_count(struct page *page)

{
@@ -18,6 +74,8 @@ static inline int page_count(struct page *page) 
static inline void set_page_count(struct page *page, int v)

{

	atomic_set(&page->_count, v);

	if (page_ref_tracepoint_active(__tracepoint_page_ref_set))

		__page_ref_set(page, v);

}



/*
@@ -32,46 +90,74 @@ static inline void init_page_count(struct page *page) 
static inline void page_ref_add(struct page *page, int nr)

{

	atomic_add(nr, &page->_count);

	if (page_ref_tracepoint_active(__tracepoint_page_ref_mod))

		__page_ref_mod(page, nr);

}



static inline void page_ref_sub(struct page *page, int nr)

{

	atomic_sub(nr, &page->_count);

	if (page_ref_tracepoint_active(__tracepoint_page_ref_mod))

		__page_ref_mod(page, -nr);

}



static inline void page_ref_inc(struct page *page)

{

	atomic_inc(&page->_count);

	if (page_ref_tracepoint_active(__tracepoint_page_ref_mod))

		__page_ref_mod(page, 1);

}



static inline void page_ref_dec(struct page *page)

{

	atomic_dec(&page->_count);

	if (page_ref_tracepoint_active(__tracepoint_page_ref_mod))

		__page_ref_mod(page, -1);

}



static inline int page_ref_sub_and_test(struct page *page, int nr)

{

	return atomic_sub_and_test(nr, &page->_count);

	int ret = atomic_sub_and_test(nr, &page->_count);



	if (page_ref_tracepoint_active(__tracepoint_page_ref_mod_and_test))

		__page_ref_mod_and_test(page, -nr, ret);

	return ret;

}



static inline int page_ref_dec_and_test(struct page *page)

{

	return atomic_dec_and_test(&page->_count);

	int ret = atomic_dec_and_test(&page->_count);



	if (page_ref_tracepoint_active(__tracepoint_page_ref_mod_and_test))

		__page_ref_mod_and_test(page, -1, ret);

	return ret;

}



static inline int page_ref_dec_return(struct page *page)

{

	return atomic_dec_return(&page->_count);

	int ret = atomic_dec_return(&page->_count);



	if (page_ref_tracepoint_active(__tracepoint_page_ref_mod_and_return))

		__page_ref_mod_and_return(page, -1, ret);

	return ret;

}



static inline int page_ref_add_unless(struct page *page, int nr, int u)

{

	return atomic_add_unless(&page->_count, nr, u);

	int ret = atomic_add_unless(&page->_count, nr, u);



	if (page_ref_tracepoint_active(__tracepoint_page_ref_mod_unless))

		__page_ref_mod_unless(page, nr, ret);

	return ret;

}



static inline int page_ref_freeze(struct page *page, int count)

{

	return likely(atomic_cmpxchg(&page->_count, count, 0) == count);

	int ret = likely(atomic_cmpxchg(&page->_count, count, 0) == count);



	if (page_ref_tracepoint_active(__tracepoint_page_ref_freeze))

		__page_ref_freeze(page, count, ret);

	return ret;

}



static inline void page_ref_unfreeze(struct page *page, int count)
@@ -80,6 +166,8 @@ static inline void page_ref_unfreeze(struct page *page, int count) 
	VM_BUG_ON(count == 0);



	atomic_set(&page->_count, count);

	if (page_ref_tracepoint_active(__tracepoint_page_ref_unfreeze))

		__page_ref_unfreeze(page, count);

}



#endif

include/trace/events/page_ref.h

0 → 100644
+134 −0
Original line number Diff line number Diff line 
#undef TRACE_SYSTEM

#define TRACE_SYSTEM page_ref



#if !defined(_TRACE_PAGE_REF_H) || defined(TRACE_HEADER_MULTI_READ)

#define _TRACE_PAGE_REF_H



#include <linux/types.h>

#include <linux/page_ref.h>

#include <linux/tracepoint.h>

#include <trace/events/mmflags.h>



DECLARE_EVENT_CLASS(page_ref_mod_template,



	TP_PROTO(struct page *page, int v),



	TP_ARGS(page, v),



	TP_STRUCT__entry(

		__field(unsigned long, pfn)

		__field(unsigned long, flags)

		__field(int, count)

		__field(int, mapcount)

		__field(void *, mapping)

		__field(int, mt)

		__field(int, val)

	),



	TP_fast_assign(

		__entry->pfn = page_to_pfn(page);

		__entry->flags = page->flags;

		__entry->count = page_ref_count(page);

		__entry->mapcount = page_mapcount(page);

		__entry->mapping = page->mapping;

		__entry->mt = get_pageblock_migratetype(page);

		__entry->val = v;

	),



	TP_printk("pfn=0x%lx flags=%s count=%d mapcount=%d mapping=%p mt=%d val=%d",

		__entry->pfn,

		show_page_flags(__entry->flags & ((1UL << NR_PAGEFLAGS) - 1)),

		__entry->count,

		__entry->mapcount, __entry->mapping, __entry->mt,

		__entry->val)

);



DEFINE_EVENT(page_ref_mod_template, page_ref_set,



	TP_PROTO(struct page *page, int v),



	TP_ARGS(page, v)

);



DEFINE_EVENT(page_ref_mod_template, page_ref_mod,



	TP_PROTO(struct page *page, int v),



	TP_ARGS(page, v)

);



DECLARE_EVENT_CLASS(page_ref_mod_and_test_template,



	TP_PROTO(struct page *page, int v, int ret),



	TP_ARGS(page, v, ret),



	TP_STRUCT__entry(

		__field(unsigned long, pfn)

		__field(unsigned long, flags)

		__field(int, count)

		__field(int, mapcount)

		__field(void *, mapping)

		__field(int, mt)

		__field(int, val)

		__field(int, ret)

	),



	TP_fast_assign(

		__entry->pfn = page_to_pfn(page);

		__entry->flags = page->flags;

		__entry->count = page_ref_count(page);

		__entry->mapcount = page_mapcount(page);

		__entry->mapping = page->mapping;

		__entry->mt = get_pageblock_migratetype(page);

		__entry->val = v;

		__entry->ret = ret;

	),



	TP_printk("pfn=0x%lx flags=%s count=%d mapcount=%d mapping=%p mt=%d val=%d ret=%d",

		__entry->pfn,

		show_page_flags(__entry->flags & ((1UL << NR_PAGEFLAGS) - 1)),

		__entry->count,

		__entry->mapcount, __entry->mapping, __entry->mt,

		__entry->val, __entry->ret)

);



DEFINE_EVENT(page_ref_mod_and_test_template, page_ref_mod_and_test,



	TP_PROTO(struct page *page, int v, int ret),



	TP_ARGS(page, v, ret)

);



DEFINE_EVENT(page_ref_mod_and_test_template, page_ref_mod_and_return,



	TP_PROTO(struct page *page, int v, int ret),



	TP_ARGS(page, v, ret)

);



DEFINE_EVENT(page_ref_mod_and_test_template, page_ref_mod_unless,



	TP_PROTO(struct page *page, int v, int ret),



	TP_ARGS(page, v, ret)

);



DEFINE_EVENT(page_ref_mod_and_test_template, page_ref_freeze,



	TP_PROTO(struct page *page, int v, int ret),



	TP_ARGS(page, v, ret)

);



DEFINE_EVENT(page_ref_mod_template, page_ref_unfreeze,



	TP_PROTO(struct page *page, int v),



	TP_ARGS(page, v)

);



#endif /* _TRACE_PAGE_COUNT_H */



/* This part must be outside protection */

#include <trace/define_trace.h>

mm/Kconfig.debug

+13 −0
Original line number Diff line number Diff line
@@ -79,3 +79,16 @@ config PAGE_POISONING_ZERO 
	   Enabling page poisoning with this option will disable hibernation



	   If unsure, say N

	bool



config DEBUG_PAGE_REF

	bool "Enable tracepoint to track down page reference manipulation"

	depends on DEBUG_KERNEL

	depends on TRACEPOINTS

	---help---

	  This is a feature to add tracepoint for tracking down page reference

	  manipulation. This tracking is useful to diagnose functional failure

	  due to migration failures caused by page reference mismatches.  Be

	  careful when enabling this feature because it adds about 30 KB to the

	  kernel code.  However the runtime performance overhead is virtually

	  nil until the tracepoints are actually enabled.

mm/Makefile

+1 −0
Original line number Diff line number Diff line
@@ -81,3 +81,4 @@ obj-$(CONFIG_CMA_DEBUGFS) += cma_debug.o 
obj-$(CONFIG_USERFAULTFD) += userfaultfd.o

obj-$(CONFIG_IDLE_PAGE_TRACKING) += page_idle.o

obj-$(CONFIG_FRAME_VECTOR) += frame_vector.o

obj-$(CONFIG_DEBUG_PAGE_REF) += debug_page_ref.o

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