Re: [PATCH 04/20 v3] powerpc/mm/fault.c: Port OOM changes to do_page_fault

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Tue, 2012-03-20 at 12:01 -0400, Kautuk Consul wrote:
> Commit d065bd810b6deb67d4897a14bfe21f8eb526ba99
> (mm: retry page fault when blocking on disk transfer) and
> commit 37b23e0525d393d48a7d59f870b3bc061a30ccdb
> (x86,mm: make pagefault killable)
> 
> The above commits introduced changes into the x86 pagefault handler
> for making the page fault handler retryable as well as killable.
> 
> These changes reduce the mmap_sem hold time, which is crucial
> during OOM killer invocation.
> 
> Port these changes to powerpc.

I have done that port already :-) It's in powerpc-next which I will send
to Linus to pull today or tomorrow....

Cheers,
Ben.

> Signed-off-by: Mohd. Faris <mohdfarisq2010@gmail.com>
> Signed-off-by: Kautuk Consul <consul.kautuk@gmail.com>
> ---
>  arch/powerpc/mm/fault.c |   51 +++++++++++++++++++++++++++++++++-------------
>  1 files changed, 36 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
> index 2f0d1b0..a3b1176 100644
> --- a/arch/powerpc/mm/fault.c
> +++ b/arch/powerpc/mm/fault.c
> @@ -129,6 +129,7 @@ int __kprobes do_page_fault(struct pt_regs *regs, unsigned long address,
>  	int is_write = 0, ret;
>  	int trap = TRAP(regs);
>   	int is_exec = trap == 0x400;
> +	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
>  
>  #if !(defined(CONFIG_4xx) || defined(CONFIG_BOOKE))
>  	/*
> @@ -212,6 +213,7 @@ int __kprobes do_page_fault(struct pt_regs *regs, unsigned long address,
>  		if (!user_mode(regs) && !search_exception_tables(regs->nip))
>  			goto bad_area_nosemaphore;
>  
> +retry:
>  		down_read(&mm->mmap_sem);
>  	}
>  
> @@ -313,6 +315,7 @@ good_area:
>  	} else if (is_write) {
>  		if (!(vma->vm_flags & VM_WRITE))
>  			goto bad_area;
> +		flags |= FAULT_FLAG_WRITE;
>  	/* a read */
>  	} else {
>  		/* protection fault */
> @@ -327,7 +330,11 @@ good_area:
>  	 * make sure we exit gracefully rather than endlessly redo
>  	 * the fault.
>  	 */
> -	ret = handle_mm_fault(mm, vma, address, is_write ? FAULT_FLAG_WRITE : 0);
> +	ret = handle_mm_fault(mm, vma, address, flags);
> +
> +	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
> +		return 0;
> +
>  	if (unlikely(ret & VM_FAULT_ERROR)) {
>  		if (ret & VM_FAULT_OOM)
>  			goto out_of_memory;
> @@ -335,22 +342,36 @@ good_area:
>  			goto do_sigbus;
>  		BUG();
>  	}
> -	if (ret & VM_FAULT_MAJOR) {
> -		current->maj_flt++;
> -		perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1,
> -				     regs, address);
> -#ifdef CONFIG_PPC_SMLPAR
> -		if (firmware_has_feature(FW_FEATURE_CMO)) {
> -			preempt_disable();
> -			get_lppaca()->page_ins += (1 << PAGE_FACTOR);
> -			preempt_enable();
> +	if (flags & FAULT_FLAG_ALLOW_RETRY) {
> +		if (ret & VM_FAULT_MAJOR) {
> +			current->maj_flt++;
> +			perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1,
> +					     regs, address);
> +#ifdef CONFIG_PPC_SMLPAR
> +			if (firmware_has_feature(FW_FEATURE_CMO)) {
> +				preempt_disable();
> +				get_lppaca()->page_ins += (1 << PAGE_FACTOR);
> +				preempt_enable();
> +			}
> +#endif
> +		} else {
> +			current->min_flt++;
> +			perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1,
> +					     regs, address);
> +		}
> +		if (fault & VM_FAULT_RETRY) {
> +			flags &= ~FAULT_FLAG_ALLOW_RETRY;
> +
> +			/*
> +			 * No need to up_read(&mm->mmap_sem) as we would
> +			 * have already released it in __lock_page_or_retry
> +			 * in mm/filemap.c.
> +			 */
> +
> +			goto retry;
>  		}
> -#endif
> -	} else {
> -		current->min_flt++;
> -		perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1,
> -				     regs, address);
>  	}
> +
>  	up_read(&mm->mmap_sem);
>  	return 0;
>