Re: [patch 10/17] LTTng instrumentation - swap

[Peter Zijlstra]

On Tue, 2008-07-15 at 18:26 -0400, Mathieu Desnoyers wrote:
> plain text document attachment (lttng-instrumentation-swap.patch)
> Instrumentation of waits caused by swap activity. Also instrumentation
> swapon/swapoff events to keep track of active swap partitions.
> 
> Those tracepoints are used by LTTng.
> 
> About the performance impact of tracepoints (which is comparable to markers),
> even without immediate values optimizations, tests done by Hideo Aoki on ia64
> show no regression. His test case was using hackbench on a kernel where
> scheduler instrumentation (about 5 events in code scheduler code) was added.
> See the "Tracepoints" patch header for performance result detail.
> 
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>
> CC: linux-mm@xxxxxxxxx
> CC: Dave Hansen <haveblue@xxxxxxxxxx>
> CC: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> CC: 'Peter Zijlstra' <peterz@xxxxxxxxxxxxx>
> CC: "Frank Ch. Eigler" <fche@xxxxxxxxxx>
> CC: 'Ingo Molnar' <mingo@xxxxxxx>
> CC: 'Hideo AOKI' <haoki@xxxxxxxxxx>
> CC: Takashi Nishiie <t-nishiie@xxxxxxxxxxxxxxxxxx>
> CC: 'Steven Rostedt' <rostedt@xxxxxxxxxxx>
> CC: Eduard - Gabriel Munteanu <eduard.munteanu@xxxxxxxxxxx>
> ---
>  include/trace/swap.h |   20 ++++++++++++++++++++
>  mm/memory.c          |    2 ++
>  mm/page_io.c         |    2 ++
>  mm/swapfile.c        |    4 ++++
>  4 files changed, 28 insertions(+)
> 
> Index: linux-2.6-lttng/mm/memory.c
> ===================================================================
> --- linux-2.6-lttng.orig/mm/memory.c	2008-07-15 13:54:46.000000000 -0400
> +++ linux-2.6-lttng/mm/memory.c	2008-07-15 14:02:54.000000000 -0400
> @@ -51,6 +51,7 @@
>  #include <linux/init.h>
>  #include <linux/writeback.h>
>  #include <linux/memcontrol.h>
> +#include <trace/swap.h>
>  
>  #include <asm/pgalloc.h>
>  #include <asm/uaccess.h>
> @@ -2213,6 +2214,7 @@ static int do_swap_page(struct mm_struct
>  		/* Had to read the page from swap area: Major fault */
>  		ret = VM_FAULT_MAJOR;
>  		count_vm_event(PGMAJFAULT);
> +		trace_swap_in(page, entry);
>  	}
>  
>  	if (mem_cgroup_charge(page, mm, GFP_KERNEL)) {
> Index: linux-2.6-lttng/mm/page_io.c
> ===================================================================
> --- linux-2.6-lttng.orig/mm/page_io.c	2008-07-15 13:54:46.000000000 -0400
> +++ linux-2.6-lttng/mm/page_io.c	2008-07-15 14:02:54.000000000 -0400
> @@ -17,6 +17,7 @@
>  #include <linux/bio.h>
>  #include <linux/swapops.h>
>  #include <linux/writeback.h>
> +#include <trace/swap.h>
>  #include <asm/pgtable.h>
>  
>  static struct bio *get_swap_bio(gfp_t gfp_flags, pgoff_t index,
> @@ -114,6 +115,7 @@ int swap_writepage(struct page *page, st
>  		rw |= (1 << BIO_RW_SYNC);
>  	count_vm_event(PSWPOUT);
>  	set_page_writeback(page);
> +	trace_swap_out(page);
>  	unlock_page(page);
>  	submit_bio(rw, bio);
>  out:
> Index: linux-2.6-lttng/mm/swapfile.c
> ===================================================================
> --- linux-2.6-lttng.orig/mm/swapfile.c	2008-07-15 13:54:46.000000000 -0400
> +++ linux-2.6-lttng/mm/swapfile.c	2008-07-15 14:02:54.000000000 -0400
> @@ -32,6 +32,7 @@
>  #include <asm/pgtable.h>
>  #include <asm/tlbflush.h>
>  #include <linux/swapops.h>
> +#include <trace/swap.h>
>  
>  DEFINE_SPINLOCK(swap_lock);
>  unsigned int nr_swapfiles;
> @@ -1310,6 +1311,7 @@ asmlinkage long sys_swapoff(const char _
>  	swap_map = p->swap_map;
>  	p->swap_map = NULL;
>  	p->flags = 0;
> +	trace_swap_file_close(swap_file);
>  	spin_unlock(&swap_lock);
>  	mutex_unlock(&swapon_mutex);
>  	vfree(swap_map);
> @@ -1695,6 +1697,7 @@ asmlinkage long sys_swapon(const char __
>  	} else {
>  		swap_info[prev].next = p - swap_info;
>  	}
> +	trace_swap_file_open(swap_file, name);
>  	spin_unlock(&swap_lock);
>  	mutex_unlock(&swapon_mutex);
>  	error = 0;
> @@ -1796,6 +1799,7 @@ get_swap_info_struct(unsigned type)
>  {
>  	return &swap_info[type];
>  }
> +EXPORT_SYMBOL_GPL(get_swap_info_struct);

I'm not too happy with this export.

>  
>  /*
>   * swap_lock prevents swap_map being freed. Don't grab an extra
> Index: linux-2.6-lttng/include/trace/swap.h
> ===================================================================
> --- /dev/null	1970-01-01 00:00:00.000000000 +0000
> +++ linux-2.6-lttng/include/trace/swap.h	2008-07-15 14:02:54.000000000 -0400
> @@ -0,0 +1,20 @@
> +#ifndef _TRACE_SWAP_H
> +#define _TRACE_SWAP_H
> +
> +#include <linux/swap.h>
> +#include <linux/tracepoint.h>
> +
> +DEFINE_TRACE(swap_in,
> +	TPPROTO(struct page *page, swp_entry_t entry),
> +	TPARGS(page, entry));
> +DEFINE_TRACE(swap_out,
> +	TPPROTO(struct page *page),
> +	TPARGS(page));
> +DEFINE_TRACE(swap_file_open,
> +	TPPROTO(struct file *file, char *filename),
> +	TPARGS(file, filename));
> +DEFINE_TRACE(swap_file_close,
> +	TPPROTO(struct file *file),
> +	TPARGS(file));
> +
> +#endif
> 

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