[lttng-dev] [RFC-Patch 2/2] x86:Instruments page fault trace event

[Mathieu Desnoyers]

* Francis Deslauriers (fdeslaur at gmail.com) wrote:
> Signed-off-by: Francis Deslauriers <fdeslaur at gmail.com>
> Reviewed-by: Raphaël Beamonte <raphael.beamonte at gmail.com>
> ---
>  arch/x86/mm/fault.c |    7 +++++++
>  mm/memory.c         |    5 +++++
>  2 files changed, 12 insertions(+)
> 
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index 2b97525..6ceaaaa 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -20,6 +20,9 @@
>  #include <asm/fixmap.h>			/* VSYSCALL_START		*/
>  #include <asm/context_tracking.h>	/* exception_enter(), ...	*/
>  
> +#define CREATE_TRACE_POINTS
> +#include <trace/events/fault.h>		/* trace_page_fault_*(), ...	*/
> +
>  /*
>   * Page fault error code bits:
>   *
> @@ -754,12 +757,14 @@ __bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
>  
>  		if (likely(show_unhandled_signals))
>  			show_signal_msg(regs, error_code, address, tsk);
> +		trace_page_fault_entry(regs, address, error_code & PF_WRITE);
>  
>  		tsk->thread.cr2		= address;
>  		tsk->thread.error_code	= error_code;
>  		tsk->thread.trap_nr	= X86_TRAP_PF;
>  
>  		force_sig_info_fault(SIGSEGV, si_code, address, tsk, 0);

maybe we should put a comment in the patch when sending to LKML, e.g.:

        /*
         * Using -1 here, since there is no VM_FAULT flag to identify
         * user accesses triggering SIGSEGV.
         */

> +		trace_page_fault_exit(-1);

And maybe interesting hints will come from LKML.

The rest looks good,

Thanks,

Mathieu

>  
>  		return;
>  	}
> @@ -1183,7 +1188,9 @@ good_area:
>  	 * make sure we exit gracefully rather than endlessly redo
>  	 * the fault:
>  	 */
> +	trace_page_fault_entry(regs, address, write);
>  	fault = handle_mm_fault(mm, vma, address, flags);
> +	trace_page_fault_exit(fault);
>  
>  	if (unlikely(fault & (VM_FAULT_RETRY|VM_FAULT_ERROR))) {
>  		if (mm_fault_error(regs, error_code, address, fault))
> diff --git a/mm/memory.c b/mm/memory.c
> index 494526a..49a8119 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -67,6 +67,8 @@
>  #include <asm/tlbflush.h>
>  #include <asm/pgtable.h>
>  
> +#include <trace/events/fault.h>
> +
>  #include "internal.h"
>  
>  #ifdef LAST_NID_NOT_IN_PAGE_FLAGS
> @@ -1828,8 +1830,11 @@ long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
>  				if (foll_flags & FOLL_NOWAIT)
>  					fault_flags |= (FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT);
>  
> +				trace_page_fault_entry(0, start,
> +						foll_flags & FOLL_WRITE);
>  				ret = handle_mm_fault(mm, vma, start,
>  							fault_flags);
> +				trace_page_fault_exit(ret);
>  
>  				if (ret & VM_FAULT_ERROR) {
>  					if (ret & VM_FAULT_OOM)
> -- 
> 1.7.10.4
> 
> 
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-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com