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The goal of these tracepoints is to be able to debug lock contention issues. This lock is acquired on most (all?) mmap / munmap / page fault operations, so a multi-threaded process which does a lot of these can experience significant contention. We trace just before we start acquisition, when the acquisition returns (whether it succeeded or not), and when the lock is released (or downgraded). The events are broken out by lock type (read / write). The events are also broken out by memcg path. For container-based workloads, users often think of several processes in a memcg as a single logical "task", so collecting statistics at this level is useful. The end goal is to get latency information. This isn't directly included in the trace events. Instead, users are expected to compute the time between "start locking" and "acquire returned", using e.g. synthetic events or BPF. The benefit we get from this is simpler code. Because we use tracepoint_enabled() to decide whether or not to trace, this patch has effectively no overhead unless tracepoints are enabled at runtime. If tracepoints are enabled, there is a performance impact, but how much depends on exactly what e.g. the BPF program does. [axelrasmussen@google.com: fix use-after-free race and css ref leak in tracepoints] Link: https://lkml.kernel.org/r/20201130233504.3725241-1-axelrasmussen@google.com [axelrasmussen@google.com: v3] Link: https://lkml.kernel.org/r/20201207213358.573750-1-axelrasmussen@google.com [rostedt@goodmis.org: in-depth examples of tracepoint_enabled() usage, and per-cpu-per-context buffer design] Link: https://lkml.kernel.org/r/20201105211739.568279-2-axelrasmussen@google.com Signed-off-by: Axel Rasmussen <axelrasmussen@google.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Ingo Molnar <mingo@redhat.com> Cc: Michel Lespinasse <walken@google.com> Cc: Daniel Jordan <daniel.m.jordan@oracle.com> Cc: Jann Horn <jannh@google.com> Cc: Chinwen Chang <chinwen.chang@mediatek.com> Cc: Davidlohr Bueso <dbueso@suse.de> Cc: David Rientjes <rientjes@google.com> Cc: Laurent Dufour <ldufour@linux.ibm.com> Cc: Yafang Shao <laoar.shao@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
108 lines
2.2 KiB
C
108 lines
2.2 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#undef TRACE_SYSTEM
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#define TRACE_SYSTEM mmap_lock
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#if !defined(_TRACE_MMAP_LOCK_H) || defined(TRACE_HEADER_MULTI_READ)
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#define _TRACE_MMAP_LOCK_H
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#include <linux/tracepoint.h>
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#include <linux/types.h>
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struct mm_struct;
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extern int trace_mmap_lock_reg(void);
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extern void trace_mmap_lock_unreg(void);
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TRACE_EVENT_FN(mmap_lock_start_locking,
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TP_PROTO(struct mm_struct *mm, const char *memcg_path, bool write),
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TP_ARGS(mm, memcg_path, write),
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TP_STRUCT__entry(
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__field(struct mm_struct *, mm)
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__string(memcg_path, memcg_path)
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__field(bool, write)
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),
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TP_fast_assign(
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__entry->mm = mm;
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__assign_str(memcg_path, memcg_path);
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__entry->write = write;
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),
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TP_printk(
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"mm=%p memcg_path=%s write=%s\n",
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__entry->mm,
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__get_str(memcg_path),
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__entry->write ? "true" : "false"
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),
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trace_mmap_lock_reg, trace_mmap_lock_unreg
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);
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TRACE_EVENT_FN(mmap_lock_acquire_returned,
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TP_PROTO(struct mm_struct *mm, const char *memcg_path, bool write,
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bool success),
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TP_ARGS(mm, memcg_path, write, success),
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TP_STRUCT__entry(
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__field(struct mm_struct *, mm)
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__string(memcg_path, memcg_path)
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__field(bool, write)
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__field(bool, success)
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),
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TP_fast_assign(
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__entry->mm = mm;
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__assign_str(memcg_path, memcg_path);
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__entry->write = write;
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__entry->success = success;
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),
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TP_printk(
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"mm=%p memcg_path=%s write=%s success=%s\n",
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__entry->mm,
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__get_str(memcg_path),
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__entry->write ? "true" : "false",
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__entry->success ? "true" : "false"
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),
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trace_mmap_lock_reg, trace_mmap_lock_unreg
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);
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TRACE_EVENT_FN(mmap_lock_released,
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TP_PROTO(struct mm_struct *mm, const char *memcg_path, bool write),
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TP_ARGS(mm, memcg_path, write),
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TP_STRUCT__entry(
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__field(struct mm_struct *, mm)
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__string(memcg_path, memcg_path)
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__field(bool, write)
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),
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TP_fast_assign(
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__entry->mm = mm;
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__assign_str(memcg_path, memcg_path);
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__entry->write = write;
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),
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TP_printk(
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"mm=%p memcg_path=%s write=%s\n",
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__entry->mm,
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__get_str(memcg_path),
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__entry->write ? "true" : "false"
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),
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trace_mmap_lock_reg, trace_mmap_lock_unreg
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);
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#endif /* _TRACE_MMAP_LOCK_H */
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/* This part must be outside protection */
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#include <trace/define_trace.h>
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