Message-Id: <1217237084.5998.5.camel@penberg-laptop>
Date:	Mon, 28 Jul 2008 12:24:44 +0300
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Eduard - Gabriel Munteanu <eduard.munteanu@...ux360.ro>
Cc:	cl@...ux-foundation.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, rdunlap@...otime.net,
	mpm@...enic.com, mathieu.desnoyers@...ymtl.ca
Subject: Re: [RFC PATCH 1/4] kmemtrace: Core implementation.

Hi,

[I'm cc'ing Mathieu if he wants to comment on this.]

On Tue, 2008-07-22 at 21:36 +0300, Eduard - Gabriel Munteanu wrote:
> kmemtrace provides tracing for slab allocator functions, such as kmalloc,
> kfree, kmem_cache_alloc, kmem_cache_free etc.. Collected data is then fed
> to the userspace application in order to analyse allocation hotspots,
> internal fragmentation and so on, making it possible to see how well an
> allocator performs, as well as debug and profile kernel code.

Reviewed-by: Pekka Enberg <penberg@...helsinki.fi>

> Signed-off-by: Eduard - Gabriel Munteanu <eduard.munteanu@...ux360.ro>
> ---
>  Documentation/ABI/testing/debugfs-kmemtrace |   58 +++++++
>  Documentation/kernel-parameters.txt         |   10 +
>  Documentation/vm/kmemtrace.txt              |  126 ++++++++++++++
>  MAINTAINERS                                 |    6 +
>  include/linux/kmemtrace.h                   |  110 ++++++++++++
>  init/main.c                                 |    2 +
>  lib/Kconfig.debug                           |   28 +++
>  mm/Makefile                                 |    2 +-
>  mm/kmemtrace.c                              |  244 +++++++++++++++++++++++++++
>  9 files changed, 585 insertions(+), 1 deletions(-)
>  create mode 100644 Documentation/ABI/testing/debugfs-kmemtrace
>  create mode 100644 Documentation/vm/kmemtrace.txt
>  create mode 100644 include/linux/kmemtrace.h
>  create mode 100644 mm/kmemtrace.c
> 
> diff --git a/Documentation/ABI/testing/debugfs-kmemtrace b/Documentation/ABI/testing/debugfs-kmemtrace
> new file mode 100644
> index 0000000..466c2bb
> --- /dev/null
> +++ b/Documentation/ABI/testing/debugfs-kmemtrace
> @@ -0,0 +1,58 @@
> +What:		/sys/kernel/debug/kmemtrace/
> +Date:		July 2008
> +Contact:	Eduard - Gabriel Munteanu <eduard.munteanu@...ux360.ro>
> +Description:
> +
> +In kmemtrace-enabled kernels, the following files are created:
> +
> +/sys/kernel/debug/kmemtrace/
> +	cpu<n>		(0400)	Per-CPU tracing data, see below. (binary)
> +	total_overruns	(0400)	Total number of bytes which were dropped from
> +				cpu<n> files because of full buffer condition,
> +				non-binary. (text)
> +	abi_version	(0400)	Kernel's kmemtrace ABI version. (text)
> +
> +Each per-CPU file should be read according to the relay interface. That is,
> +the reader should set affinity to that specific CPU and, as currently done by
> +the userspace application (though there are other methods), use poll() with
> +an infinite timeout before every read(). Otherwise, erroneous data may be
> +read. The binary data has the following _core_ format:
> +	Event id	(1 byte)	Unsigned integer, one of:
> +		0 - erroneous event, this is illegal/invalid data and must
> +		    not occur (KMEMTRACE_EVENT_NULL)
> +		1 - represents an allocation (KMEMTRACE_EVENT_ALLOC)
> +		2 - represents a freeing of previously allocated memory
> +		    (KMEMTRACE_EVENT_FREE)
> +	Type id		(1 byte)	Unsigned integer, one of:
> +		0 - this is a kmalloc() / kfree()
> +		1 - this is a kmem_cache_alloc() / kmem_cache_free()
> +		2 - this is a __get_free_pages() et al.
> +	Event size	(2 bytes)	Unsigned integer representing the
> +					size of this event. Used to extend
> +					kmemtrace. Discard the bytes you
> +					don't know about.
> +	Target CPU	(4 bytes)	Signed integer, valid for event id 1.
> +					If equal to -1, target CPU is the same
> +					as origin CPU, but the reverse might
> +					not be true.
> +	Caller address	(8 bytes)	Return address to the caller.
> +	Pointer to mem	(8 bytes)	Pointer to allocated memory, must not
> +					be NULL.
> +	Requested bytes	(8 bytes)	Total number of requested bytes,
> +					unsigned, must not be zero.
> +	Allocated bytes (8 bytes)	Total number of actually allocated
> +					bytes, unsigned, must not be lower
> +					than requested bytes.
> +	Requested flags	(8 bytes)	GFP flags supplied by the caller.
> +	Timestamp	(8 bytes)	Signed integer representing timestamp.
> +
> +The data is made available in the same endianness the machine has.
> +
> +Other event ids and type ids may be defined and added. Other fields may be
> +added by increasing event size. Every modification to the ABI, including
> +new id definitions, are followed by bumping the ABI version by one.
> +
> +
> +Users:
> +	kmemtrace-user - git://repo.or.cz/kmemtrace-user.git
> +
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index b52f47d..446a257 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -49,6 +49,7 @@ parameter is applicable:
>  	ISAPNP	ISA PnP code is enabled.
>  	ISDN	Appropriate ISDN support is enabled.
>  	JOY	Appropriate joystick support is enabled.
> +	KMEMTRACE kmemtrace is enabled.
>  	LIBATA  Libata driver is enabled
>  	LP	Printer support is enabled.
>  	LOOP	Loopback device support is enabled.
> @@ -941,6 +942,15 @@ and is between 256 and 4096 characters. It is defined in the file
>  			use the HighMem zone if it exists, and the Normal
>  			zone if it does not.
>  
> +	kmemtrace.enable=	[KNL,KMEMTRACE] Format: { yes | no }
> +				Controls whether kmemtrace is enabled
> +				at boot-time.
> +
> +	kmemtrace.subbufs=n	[KNL,KMEMTRACE] Overrides the number of
> +			subbufs kmemtrace's relay channel has. Set this
> +			higher than default (KMEMTRACE_N_SUBBUFS in code) if
> +			you experience buffer overruns.
> +
>  	movablecore=nn[KMG]	[KNL,X86-32,IA-64,PPC,X86-64] This parameter
>  			is similar to kernelcore except it specifies the
>  			amount of memory used for migratable allocations.
> diff --git a/Documentation/vm/kmemtrace.txt b/Documentation/vm/kmemtrace.txt
> new file mode 100644
> index 0000000..75360b1
> --- /dev/null
> +++ b/Documentation/vm/kmemtrace.txt
> @@ -0,0 +1,126 @@
> +			kmemtrace - Kernel Memory Tracer
> +
> +			  by Eduard - Gabriel Munteanu
> +			     <eduard.munteanu@...ux360.ro>
> +
> +I. Introduction
> +===============
> +
> +kmemtrace helps kernel developers figure out two things:
> +1) how different allocators (SLAB, SLUB etc.) perform
> +2) how kernel code allocates memory and how much
> +
> +To do this, we trace every allocation and export information to the userspace
> +through the relay interface. We export things such as the number of requested
> +bytes, the number of bytes actually allocated (i.e. including internal
> +fragmentation), whether this is a slab allocation or a plain kmalloc() and so
> +on.
> +
> +The actual analysis is performed by a userspace tool (see section III for
> +details on where to get it from). It logs the data exported by the kernel,
> +processes it and (as of writing this) can provide the following information:
> +- the total amount of memory allocated and fragmentation per call-site
> +- the amount of memory allocated and fragmentation per allocation
> +- total memory allocated and fragmentation in the collected dataset
> +- number of cross-CPU allocation and frees (makes sense in NUMA environments)
> +
> +Moreover, it can potentially find inconsistent and erroneous behavior in
> +kernel code, such as using slab free functions on kmalloc'ed memory or
> +allocating less memory than requested (but not truly failed allocations).
> +
> +kmemtrace also makes provisions for tracing on some arch and analysing the
> +data on another.
> +
> +II. Design and goals
> +====================
> +
> +kmemtrace was designed to handle rather large amounts of data. Thus, it uses
> +the relay interface to export whatever is logged to userspace, which then
> +stores it. Analysis and reporting is done asynchronously, that is, after the
> +data is collected and stored. By design, it allows one to log and analyse
> +on different machines and different arches.
> +
> +As of writing this, the ABI is not considered stable, though it might not
> +change much. However, no guarantees are made about compatibility yet. When
> +deemed stable, the ABI should still allow easy extension while maintaining
> +backward compatibility. This is described further in Documentation/ABI.
> +
> +Summary of design goals:
> +	- allow logging and analysis to be done across different machines
> +	- be fast and anticipate usage in high-load environments (*)
> +	- be reasonably extensible
> +	- make it possible for GNU/Linux distributions to have kmemtrace
> +	included in their repositories
> +
> +(*) - one of the reasons Pekka Enberg's original userspace data analysis
> +    tool's code was rewritten from Perl to C (although this is more than a
> +    simple conversion)
> +
> +
> +III. Quick usage guide
> +======================
> +
> +1) Get a kernel that supports kmemtrace and build it accordingly (i.e. enable
> +CONFIG_KMEMTRACE and CONFIG_DEFAULT_ENABLED).
> +
> +2) Get the userspace tool and build it:
> +$ git-clone git://repo.or.cz/kmemtrace-user.git		# current repository
> +$ cd kmemtrace-user/
> +$ ./autogen.sh
> +$ ./configure
> +$ make
> +
> +3) Boot the kmemtrace-enabled kernel if you haven't, preferably in the
> +'single' runlevel (so that relay buffers don't fill up easily), and run
> +kmemtrace:
> +# '$' does not mean user, but root here.
> +$ mount -t debugfs none /sys/kernel/debug
> +$ mount -t proc none /proc
> +$ cd path/to/kmemtrace-user/
> +$ ./kmemtraced
> +Wait a bit, then stop it with CTRL+C.
> +$ cat /sys/kernel/debug/kmemtrace/total_overruns	# Check if we didn't
> +							# overrun, should
> +							# be zero.
> +$ (Optionally) [Run kmemtrace_check separately on each cpu[0-9]*.out file to
> +		check its correctness]
> +$ ./kmemtrace-report
> +
> +Now you should have a nice and short summary of how the allocator performs.
> +
> +IV. FAQ and known issues
> +========================
> +
> +Q: 'cat /sys/kernel/debug/kmemtrace/total_overruns' is non-zero, how do I fix
> +this? Should I worry?
> +A: If it's non-zero, this affects kmemtrace's accuracy, depending on how
> +large the number is. You can fix it by supplying a higher
> +'kmemtrace.subbufs=N' kernel parameter.
> +---
> +
> +Q: kmemtrace_check reports errors, how do I fix this? Should I worry?
> +A: This is a bug and should be reported. It can occur for a variety of
> +reasons:
> +	- possible bugs in relay code
> +	- possible misuse of relay by kmemtrace
> +	- timestamps being collected unorderly
> +Or you may fix it yourself and send us a patch.
> +---
> +
> +Q: kmemtrace_report shows many errors, how do I fix this? Should I worry?
> +A: This is a known issue and I'm working on it. These might be true errors
> +in kernel code, which may have inconsistent behavior (e.g. allocating memory
> +with kmem_cache_alloc() and freeing it with kfree()). Pekka Enberg pointed
> +out this behavior may work with SLAB, but may fail with other allocators.
> +
> +It may also be due to lack of tracing in some unusual allocator functions.
> +
> +We don't want bug reports regarding this issue yet.
> +---
> +
> +V. See also
> +===========
> +
> +Documentation/kernel-parameters.txt
> +Documentation/ABI/testing/debugfs-kmemtrace
> +
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 56a2f67..e967bc2 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -2425,6 +2425,12 @@ M:	jason.wessel@...driver.com
>  L:	kgdb-bugreport@...ts.sourceforge.net
>  S:	Maintained
>  
> +KMEMTRACE
> +P:	Eduard - Gabriel Munteanu
> +M:	eduard.munteanu@...ux360.ro
> +L:	linux-kernel@...r.kernel.org
> +S:	Maintained
> +
>  KPROBES
>  P:	Ananth N Mavinakayanahalli
>  M:	ananth@...ibm.com
> diff --git a/include/linux/kmemtrace.h b/include/linux/kmemtrace.h
> new file mode 100644
> index 0000000..48746ee
> --- /dev/null
> +++ b/include/linux/kmemtrace.h
> @@ -0,0 +1,110 @@
> +/*
> + * Copyright (C) 2008 Eduard - Gabriel Munteanu
> + *
> + * This file is released under GPL version 2.
> + */
> +
> +#ifndef _LINUX_KMEMTRACE_H
> +#define _LINUX_KMEMTRACE_H
> +
> +#ifdef __KERNEL__
> +
> +#include <linux/types.h>
> +#include <linux/marker.h>
> +
> +/* ABI definition starts here. */
> +
> +#define KMEMTRACE_ABI_VERSION		1
> +
> +enum kmemtrace_event_id {
> +	KMEMTRACE_EVENT_NULL = 0,	/* Erroneous event. */
> +	KMEMTRACE_EVENT_ALLOC,
> +	KMEMTRACE_EVENT_FREE,
> +};
> +
> +enum kmemtrace_type_id {
> +	KMEMTRACE_TYPE_KMALLOC = 0,	/* kmalloc() / kfree(). */
> +	KMEMTRACE_TYPE_CACHE,		/* kmem_cache_*(). */
> +	KMEMTRACE_TYPE_PAGES,		/* __get_free_pages() and friends. */
> +};
> +
> +struct kmemtrace_event {
> +	u8		event_id;	/* Allocate or free? */
> +	u8		type_id;	/* Kind of allocation/free. */
> +	u16		event_size;	/* Size of event */
> +	s32		node;		/* Target CPU. */
> +	u64		call_site;	/* Caller address. */
> +	u64		ptr;		/* Pointer to allocation. */
> +	u64		bytes_req;	/* Number of bytes requested. */
> +	u64		bytes_alloc;	/* Number of bytes allocated. */
> +	u64		gfp_flags;	/* Requested flags. */
> +	s64		timestamp;	/* When the operation occured in ns. */
> +} __attribute__ ((__packed__));
> +
> +/* End of ABI definition. */
> +
> +#ifdef CONFIG_KMEMTRACE
> +
> +extern void kmemtrace_init(void);
> +
> +static inline void kmemtrace_mark_alloc_node(enum kmemtrace_type_id type_id,
> +					     unsigned long call_site,
> +					     const void *ptr,
> +					     size_t bytes_req,
> +					     size_t bytes_alloc,
> +					     gfp_t gfp_flags,
> +					     int node)
> +{
> +	trace_mark(kmemtrace_alloc, "type_id %d call_site %lu ptr %lu "
> +		   "bytes_req %lu bytes_alloc %lu gfp_flags %lu node %d",
> +		   type_id, call_site, (unsigned long) ptr,
> +		   bytes_req, bytes_alloc, (unsigned long) gfp_flags, node);
> +}
> +
> +static inline void kmemtrace_mark_free(enum kmemtrace_type_id type_id,
> +				       unsigned long call_site,
> +				       const void *ptr)
> +{
> +	trace_mark(kmemtrace_free, "type_id %d call_site %lu ptr %lu",
> +		   type_id, call_site, (unsigned long) ptr);
> +}
> +
> +#else /* CONFIG_KMEMTRACE */
> +
> +static inline void kmemtrace_init(void)
> +{
> +}
> +
> +static inline void kmemtrace_mark_alloc_node(enum kmemtrace_type_id type_id,
> +					     unsigned long call_site,
> +					     const void *ptr,
> +					     size_t bytes_req,
> +					     size_t bytes_alloc,
> +					     gfp_t gfp_flags,
> +					     int node)
> +{
> +}
> +
> +static inline void kmemtrace_mark_free(enum kmemtrace_type_id type_id,
> +				       unsigned long call_site,
> +				       const void *ptr)
> +{
> +}
> +
> +#endif /* CONFIG_KMEMTRACE */
> +
> +static inline void kmemtrace_mark_alloc(enum kmemtrace_type_id type_id,
> +					unsigned long call_site,
> +					const void *ptr,
> +					size_t bytes_req,
> +					size_t bytes_alloc,
> +					gfp_t gfp_flags)
> +{
> +	kmemtrace_mark_alloc_node(type_id, call_site, ptr,
> +				  bytes_req, bytes_alloc, gfp_flags, -1);
> +}
> +
> +#endif /* __KERNEL__ */
> +
> +#endif /* _LINUX_KMEMTRACE_H */
> +
> diff --git a/init/main.c b/init/main.c
> index 057f364..c00659c 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -66,6 +66,7 @@
>  #include <asm/setup.h>
>  #include <asm/sections.h>
>  #include <asm/cacheflush.h>
> +#include <linux/kmemtrace.h>
>  
>  #ifdef CONFIG_X86_LOCAL_APIC
>  #include <asm/smp.h>
> @@ -641,6 +642,7 @@ asmlinkage void __init start_kernel(void)
>  	enable_debug_pagealloc();
>  	cpu_hotplug_init();
>  	kmem_cache_init();
> +	kmemtrace_init();
>  	debug_objects_mem_init();
>  	idr_init_cache();
>  	setup_per_cpu_pageset();
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index d2099f4..0ade2ae 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -674,6 +674,34 @@ config FIREWIRE_OHCI_REMOTE_DMA
>  
>  	  If unsure, say N.
>  
> +config KMEMTRACE
> +	bool "Kernel memory tracer (kmemtrace)"
> +	depends on RELAY && DEBUG_FS && MARKERS
> +	help
> +	  kmemtrace provides tracing for slab allocator functions, such as
> +	  kmalloc, kfree, kmem_cache_alloc, kmem_cache_free etc.. Collected
> +	  data is then fed to the userspace application in order to analyse
> +	  allocation hotspots, internal fragmentation and so on, making it
> +	  possible to see how well an allocator performs, as well as debug
> +	  and profile kernel code.
> +
> +	  This requires an userspace application to use. See
> +	  Documentation/vm/kmemtrace.txt for more information.
> +
> +	  Saying Y will make the kernel somewhat larger and slower. However,
> +	  if you disable kmemtrace at run-time or boot-time, the performance
> +	  impact is minimal (depending on the arch the kernel is built for).
> +
> +	  If unsure, say N.
> +
> +config KMEMTRACE_DEFAULT_ENABLED
> +	bool "Enabled by default at boot"
> +	depends on KMEMTRACE
> +	help
> +	  Say Y here to enable kmemtrace at boot-time by default. Whatever
> +	  the choice, the behavior can be overridden by a kernel parameter,
> +	  as described in documentation.
> +
>  source "samples/Kconfig"
>  
>  source "lib/Kconfig.kgdb"
> diff --git a/mm/Makefile b/mm/Makefile
> index 18c143b..d88a3bc 100644
> --- a/mm/Makefile
> +++ b/mm/Makefile
> @@ -33,4 +33,4 @@ obj-$(CONFIG_MIGRATION) += migrate.o
>  obj-$(CONFIG_SMP) += allocpercpu.o
>  obj-$(CONFIG_QUICKLIST) += quicklist.o
>  obj-$(CONFIG_CGROUP_MEM_RES_CTLR) += memcontrol.o
> -
> +obj-$(CONFIG_KMEMTRACE) += kmemtrace.o
> diff --git a/mm/kmemtrace.c b/mm/kmemtrace.c
> new file mode 100644
> index 0000000..4b33ace
> --- /dev/null
> +++ b/mm/kmemtrace.c
> @@ -0,0 +1,244 @@
> +/*
> + * Copyright (C) 2008 Pekka Enberg, Eduard - Gabriel Munteanu
> + *
> + * This file is released under GPL version 2.
> + */
> +
> +#include <linux/string.h>
> +#include <linux/debugfs.h>
> +#include <linux/relay.h>
> +#include <linux/module.h>
> +#include <linux/marker.h>
> +#include <linux/gfp.h>
> +#include <linux/kmemtrace.h>
> +
> +#define KMEMTRACE_SUBBUF_SIZE	(8192 * sizeof(struct kmemtrace_event))
> +#define KMEMTRACE_N_SUBBUFS	20
> +
> +static struct rchan *kmemtrace_chan;
> +static u32 kmemtrace_buf_overruns;
> +
> +static unsigned int kmemtrace_n_subbufs;
> +#ifdef CONFIG_KMEMTRACE_DEFAULT_ENABLED
> +static unsigned int kmemtrace_enabled = 1;
> +#else
> +static unsigned int kmemtrace_enabled = 0;
> +#endif
> +
> +static u32 kmemtrace_abi_version __read_mostly = KMEMTRACE_ABI_VERSION;
> +
> +static inline void kmemtrace_log_event(struct kmemtrace_event *event)
> +{
> +	relay_write(kmemtrace_chan, event, sizeof(struct kmemtrace_event));
> +}
> +
> +static void kmemtrace_probe_alloc(void *probe_data, void *call_data,
> +				  const char *format, va_list *args)
> +{
> +	unsigned long flags;
> +	struct kmemtrace_event ev;
> +
> +	/*
> +	 * Don't convert this to use structure initializers,
> +	 * C99 does not guarantee the rvalues evaluation order.
> +	 */
> +	ev.event_id = KMEMTRACE_EVENT_ALLOC;
> +	ev.type_id = va_arg(*args, int);
> +	ev.event_size = sizeof(struct kmemtrace_event);
> +	ev.call_site = va_arg(*args, unsigned long);
> +	ev.ptr = va_arg(*args, unsigned long);
> +	/* Don't trace ignored allocations. */
> +	if (!ev.ptr)
> +		return;
> +	ev.bytes_req = va_arg(*args, unsigned long);
> +	ev.bytes_alloc = va_arg(*args, unsigned long);
> +	/* ev.timestamp set below, to preserve event ordering. */
> +	ev.gfp_flags = va_arg(*args, unsigned long);
> +	ev.node = va_arg(*args, int);
> +
> +	/* We disable IRQs for timestamps to match event ordering. */
> +	local_irq_save(flags);
> +	ev.timestamp = ktime_to_ns(ktime_get());
> +	kmemtrace_log_event(&ev);
> +	local_irq_restore(flags);
> +}
> +
> +static void kmemtrace_probe_free(void *probe_data, void *call_data,
> +				 const char *format, va_list *args)
> +{
> +	unsigned long flags;
> +	struct kmemtrace_event ev;
> +
> +	/*
> +	 * Don't convert this to use structure initializers,
> +	 * C99 does not guarantee the rvalues evaluation order.
> +	 */
> +	ev.event_id = KMEMTRACE_EVENT_FREE;
> +	ev.type_id = va_arg(*args, int);
> +	ev.event_size = sizeof(struct kmemtrace_event);
> +	ev.call_site = va_arg(*args, unsigned long);
> +	ev.ptr = va_arg(*args, unsigned long);
> +	/* Don't trace ignored allocations. */
> +	if (!ev.ptr)
> +		return;
> +	/* ev.timestamp set below, to preserve event ordering. */
> +
> +	/* We disable IRQs for timestamps to match event ordering. */
> +	local_irq_save(flags);
> +	ev.timestamp = ktime_to_ns(ktime_get());
> +	kmemtrace_log_event(&ev);
> +	local_irq_restore(flags);
> +}
> +
> +static struct dentry *
> +kmemtrace_create_buf_file(const char *filename, struct dentry *parent,
> +			  int mode, struct rchan_buf *buf, int *is_global)
> +{
> +	return debugfs_create_file(filename, mode, parent, buf,
> +				   &relay_file_operations);
> +}
> +
> +static int kmemtrace_remove_buf_file(struct dentry *dentry)
> +{
> +	debugfs_remove(dentry);
> +
> +	return 0;
> +}
> +
> +static int kmemtrace_count_overruns(struct rchan_buf *buf,
> +				    void *subbuf, void *prev_subbuf,
> +				    size_t prev_padding)
> +{
> +	if (relay_buf_full(buf)) {
> +		/*
> +		 * We know it's not SMP-safe, but neither
> +		 * debugfs_create_u32() is.
> +		 */
> +		kmemtrace_buf_overruns++;
> +		return 0;
> +	}
> +
> +	return 1;
> +}
> +
> +static struct rchan_callbacks relay_callbacks = {
> +	.create_buf_file = kmemtrace_create_buf_file,
> +	.remove_buf_file = kmemtrace_remove_buf_file,
> +	.subbuf_start = kmemtrace_count_overruns,
> +};
> +
> +static struct dentry *kmemtrace_dir;
> +static struct dentry *kmemtrace_overruns_dentry;
> +static struct dentry *kmemtrace_abi_version_dentry;
> +
> +static void kmemtrace_cleanup(void)
> +{
> +	marker_probe_unregister("kmemtrace_alloc", kmemtrace_probe_alloc, NULL);
> +	marker_probe_unregister("kmemtrace_free", kmemtrace_probe_free, NULL);
> +
> +	if (kmemtrace_abi_version_dentry)
> +		debugfs_remove(kmemtrace_abi_version_dentry);
> +	if (kmemtrace_overruns_dentry)
> +		debugfs_remove(kmemtrace_overruns_dentry);
> +
> +	relay_close(kmemtrace_chan);
> +	kmemtrace_chan = NULL;
> +
> +	if (kmemtrace_dir)
> +		debugfs_remove(kmemtrace_dir);
> +}
> +
> +static int __init kmemtrace_setup_late(void)
> +{
> +	if (!kmemtrace_chan)
> +		goto failed;
> +
> +	kmemtrace_dir = debugfs_create_dir("kmemtrace", NULL);
> +	if (!kmemtrace_dir)
> +		goto cleanup;
> +
> +	kmemtrace_abi_version_dentry =
> +		debugfs_create_u32("abi_version", S_IRUSR,
> +				   kmemtrace_dir, &kmemtrace_abi_version);
> +	kmemtrace_overruns_dentry =
> +		debugfs_create_u32("total_overruns", S_IRUSR,
> +				   kmemtrace_dir, &kmemtrace_buf_overruns);
> +	if (!kmemtrace_overruns_dentry || !kmemtrace_abi_version_dentry)
> +		goto cleanup;
> +
> +	if (relay_late_setup_files(kmemtrace_chan, "cpu", kmemtrace_dir))
> +		goto cleanup;
> +
> +	printk(KERN_INFO "kmemtrace: fully up.\n");
> +
> +	return 0;
> +
> +cleanup:
> +	kmemtrace_cleanup();
> +failed:
> +	return 1;
> +}
> +late_initcall(kmemtrace_setup_late);
> +
> +static int __init kmemtrace_set_boot_enabled(char *str)
> +{
> +	if (!str)
> +		return -EINVAL;
> +
> +	if (!strcmp(str, "yes"))
> +		kmemtrace_enabled = 1;
> +	else if (!strcmp(str, "no"))
> +		kmemtrace_enabled = 0;
> +	else
> +		return -EINVAL;
> +
> +	return 0;
> +}
> +early_param("kmemtrace.enable", kmemtrace_set_boot_enabled);
> +
> +static int __init kmemtrace_set_subbufs(char *str)
> +{
> +	get_option(&str, &kmemtrace_n_subbufs);
> +	return 0;
> +}
> +early_param("kmemtrace.subbufs", kmemtrace_set_subbufs);
> +
> +void kmemtrace_init(void)
> +{
> +	int err;
> +
> +	if (!kmemtrace_enabled)
> +		return;
> +
> +	if (!kmemtrace_n_subbufs)
> +		kmemtrace_n_subbufs = KMEMTRACE_N_SUBBUFS;
> +
> +	kmemtrace_chan = relay_open(NULL, NULL, KMEMTRACE_SUBBUF_SIZE,
> +				    kmemtrace_n_subbufs, &relay_callbacks,
> +				    NULL);
> +	if (!kmemtrace_chan) {
> +		printk(KERN_INFO "kmemtrace: could not open relay channel\n");
> +		return;
> +	}
> +
> +	err = marker_probe_register("kmemtrace_alloc", "type_id %d "
> +				    "call_site %lu ptr %lu "
> +				    "bytes_req %lu bytes_alloc %lu "
> +				    "gfp_flags %lu node %d",
> +				    kmemtrace_probe_alloc, NULL);
> +	if (err)
> +		goto probe_fail;
> +	err = marker_probe_register("kmemtrace_free", "type_id %d "
> +				    "call_site %lu ptr %lu",
> +				    kmemtrace_probe_free, NULL);
> +	if (err)
> +		goto probe_fail;
> +
> +	printk(KERN_INFO "kmemtrace: early init successful.\n");
> +	return;
> +
> +probe_fail:
> +	printk(KERN_INFO "kmemtrace: could not register marker probes!\n");
> +	kmemtrace_cleanup();
> +}
> +

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