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Date: Mon, 28 Jul 2008 12:09:23 -0500
From: Matt Mackall <mpm@...enic.com>
To: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc: Pekka Enberg <penberg@...helsinki.fi>,
Eduard - Gabriel Munteanu <eduard.munteanu@...ux360.ro>,
cl@...ux-foundation.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, rdunlap@...otime.net,
Steven Rostedt <rostedt@...dmis.org>,
Thomas Gleixner <tglx@...utronix.de>,
Michael Kerrisk <michael.kerrisk@...glemail.com>
Subject: Re: [RFC PATCH 1/4] kmemtrace: Core implementation.
On Mon, 2008-07-28 at 12:29 -0400, Mathieu Desnoyers wrote:
> * Pekka Enberg (penberg@...helsinki.fi) wrote:
> > 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
>
> Documentation should probably come in a separate patch.
We've also a new Documentation/ maintainer these days (in addition to
Randy) who should get cc:ed:
Michael Kerrisk <michael.kerrisk@...glemail.com>
> > > @@ -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)
>
> Hmm ? why record an invalid event ?? I see it's not used in the code, is
> that actually used in some way because the memory is set to 0 ?
>
>
> > > + 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.
>
> If only valid for event ID 1 and only in NUMA case, please don't waste
> space in each event header and make that a event-specific field... ?
>
> > > + Caller address (8 bytes) Return address to the caller.
>
> Not true on 32 bits machines. You are wasting 4 bytes on those archs.
>
> > > + Pointer to mem (8 bytes) Pointer to allocated memory, must not
> > > + be NULL.
>
> Same here.
>
> > > + Requested bytes (8 bytes) Total number of requested bytes,
> > > + unsigned, must not be zero.
>
> Same here.
>
> > > + Allocated bytes (8 bytes) Total number of actually allocated
> > > + bytes, unsigned, must not be lower
> > > + than requested bytes.
>
> And here.
>
> > > + Requested flags (8 bytes) GFP flags supplied by the caller.
>
> 8 bytes for GFP flags ?? Whoah, that's a lot of one-hot bits ! :) I knew
> that some allocators were bloated, bit not that much. :)
>
> > > + Timestamp (8 bytes) Signed integer representing timestamp.
> > > +
>
> With a heartbeat, as lttng does, you can cut that to a 4 bytes field.
>
> > > +The data is made available in the same endianness the machine has.
> > > +
>
> Using a magic number in the trace header lets you deal with
> cross-endianness.
>
> Saving the type sizes in the trace header lets you deal with different
> int/long/pointer type sizes.
>
> > > +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.
> > > +
>
> I personally prefer a self-describing trace :)
>
> > > +
> > > +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.
> > > +
>
> That kind of stuff would be nice to have in lttng.
>
> > > 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
>
> Not currently true : cross-endianness/wastes space for 32 bits archs.
>
> > > + - be fast and anticipate usage in high-load environments (*)
>
> LTTng will be faster though : per-cpu atomic ops instead of interrupt
> disable makes the probe faster.
>
> > > + - be reasonably extensible
>
> Automatic description of markers and dynamic assignation of IDs to
> markers should provide a bit more flexibility here.
>
>
> > > + - 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:
> > > +# '$' does not mean user, but root here.
>
> Change the documentation to prefix a root command line by "#" instead of
> leaving this weird comment.
>
> > > +$ 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.
>
> What in the world can be causing that ? Shouldn't it be fixed ? It might
> be due to unexpected allocator behavior, non-instrumented alloc/free
> code or broken tracer....
>
>
> > > +---
> > > +
> > > +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__));
> > > +
>
> See below for detail, but this event record is way too big and not
> adapted to 32 bits architectures.
>
> > > +/* 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);
> > > +}
>
> This could be trivially turned into a tracepoint probe.
>
> > > +
> > > +#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
> > > +
>
> Isn't this overridable by a command line param ? Shouldn't it be called
> "DEFAULT_KMEMTRACE_*" then ?
>
> > > +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
>
> Hrm, I'd leave that as a kernel command line option, not config option.
> If you ever want to _aways_ have it on, then change your lilo/grub file.
>
> > > +
> > > +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);
>
> Argh, and you do a supplementary copy here. You could simply alias the
> buffers and write directly to them after reserving the correct amount of
> space.
>
> > > + /* 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());
>
> ktime_get is monotonic, but with potentially coarse granularity. I see
> that you use ktime_to_ns here, which gives you a resolution of 1 timer
> tick in the case where the TSCs are not synchronized. While it should be
> "good enough" for the scheduler, I doubt it's enough for a tracer.
>
> It also takes the xtime seqlock, which adds a potentially big delay to
> the tracing code (if you read the clock while the writer lock is taken).
>
> Also, when NTP modifies the clock, although it stays monotonic, the rate
> at which it increments can dramatically change. I doubt you want to use
> that as a reference for performance analysis.
>
>
> > > + 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"))
>
> I think the standard is to use =0, =1 here, not =yes, =no ?
>
> Mathieu
>
> > > + 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();
> > > +}
> > > +
> >
>
> --
> Mathieu Desnoyers
> OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
> --
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