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Message-ID: <20111113103202.GG27746@n2100.arm.linux.org.uk>
Date: Sun, 13 Nov 2011 10:32:02 +0000
From: Russell King - ARM Linux <linux@....linux.org.uk>
To: Kautuk Consul <consul.kautuk@...il.com>
Cc: Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will.deacon@....com>, Ingo Molnar <mingo@...e.hu>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1 v3] arch/arm/mm/fault.c: Porting OOM changes into
__do_page_fault
On Sat, Nov 12, 2011 at 08:32:26PM -0500, Kautuk Consul wrote:
> Commits d065bd810b6deb67d4897a14bfe21f8eb526ba99 and
> 37b23e0525d393d48a7d59f870b3bc061a30ccdb introduced changes into
> the x86 pagefault handler for making the page fault handler
> retryable as well as killable.
Please include the summary of those commit IDs in the description.
> These changes reduce the mmap_sem hold time(for x86), which is crucial
> during OOM killer invocation.
We don't need (for x86) because that's not really relevant, and also
implied by the above paragraph.
> Porting these changes to ARM.
"Port" not "Porting" - it's not something that happens continuously
(or even something that happens each time the commit text is read!)
>
> Without these changes, my ARM board encounters many hang and livelock
> scenarios.
> After applying this patch, OOM feature performance improves according to
> my testing.
>
> Motivation for porting these changes:
> ------------------------------------
> Embedded devices such as SMART TVs and SMART phones have the capability
> to download and run apps from the internet.
> Due to this, the device user might run some malignant app that
> allocates too much memory.
> In that case, OOM killer performance is very important so that the
> device can free up memory for other apps as well as the kernel.
>
> Signed-off-by: Kautuk Consul <consul.kautuk@...il.com>
This now looks better, thanks.
I don't think we need the "motivation" section in here - it should be
below the '---'.
> ---
> arch/arm/mm/fault.c | 50 ++++++++++++++++++++++++++++++++++++++------------
> 1 files changed, 38 insertions(+), 12 deletions(-)
>
> diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
> index aa33949..9aeba03 100644
> --- a/arch/arm/mm/fault.c
> +++ b/arch/arm/mm/fault.c
> @@ -231,7 +231,7 @@ static inline bool access_error(unsigned int fsr, struct vm_area_struct *vma)
>
> static int __kprobes
> __do_page_fault(struct mm_struct *mm, unsigned long addr, unsigned int fsr,
> - struct task_struct *tsk)
> + unsigned int flags, struct task_struct *tsk)
> {
> struct vm_area_struct *vma;
> int fault;
> @@ -257,13 +257,9 @@ good_area:
> * If for any reason at all we couldn't handle the fault, make
> * sure we exit gracefully rather than endlessly redo the fault.
> */
> - fault = handle_mm_fault(mm, vma, addr & PAGE_MASK, (fsr & FSR_WRITE) ? FAULT_FLAG_WRITE : 0);
> + fault = handle_mm_fault(mm, vma, addr & PAGE_MASK, flags);
> if (unlikely(fault & VM_FAULT_ERROR))
> return fault;
> - if (fault & VM_FAULT_MAJOR)
> - tsk->maj_flt++;
> - else
> - tsk->min_flt++;
> return fault;
>
> check_stack:
> @@ -279,6 +275,9 @@ do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
> struct task_struct *tsk;
> struct mm_struct *mm;
> int fault, sig, code;
> + int write = fsr & FSR_WRITE;
> + unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE |
> + (write ? FAULT_FLAG_WRITE : 0);
>
> if (notify_page_fault(regs, fsr))
> return 0;
> @@ -305,6 +304,7 @@ do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
> if (!down_read_trylock(&mm->mmap_sem)) {
> if (!user_mode(regs) && !search_exception_tables(regs->ARM_pc))
> goto no_context;
> +retry:
> down_read(&mm->mmap_sem);
> } else {
> /*
> @@ -320,14 +320,40 @@ do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
> #endif
> }
>
> - fault = __do_page_fault(mm, addr, fsr, tsk);
> - up_read(&mm->mmap_sem);
> + fault = __do_page_fault(mm, addr, fsr, flags, tsk);
> +
> + /* If we need to retry but a fatal signal is pending, handle the
> + * signal first. We do not need to release the mmap_sem because
> + * it would already be released in __lock_page_or_retry in
> + * mm/filemap.c. */
> + if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
> + return 0;
>
> + /*
> + * Major/minor page fault accounting is only done on the
> + * initial attempt. If we go through a retry, it is extremely
> + * likely that the page will be found in page cache at that point.
> + */
> perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, addr);
> - if (fault & VM_FAULT_MAJOR)
> - perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1, regs, addr);
> - else if (fault & VM_FAULT_MINOR)
> - perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1, regs, addr);
> + if (flags & FAULT_FLAG_ALLOW_RETRY) {
> + if (fault & VM_FAULT_MAJOR) {
> + tsk->maj_flt++;
> + perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1,
> + regs, addr);
> + } else {
> + tsk->min_flt++;
> + perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1,
> + regs, addr);
> + }
> + if (fault & VM_FAULT_RETRY) {
> + /* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
> + * of starvation. */
> + flags &= ~FAULT_FLAG_ALLOW_RETRY;
> + goto retry;
> + }
> + }
> +
> + up_read(&mm->mmap_sem);
>
> /*
> * Handle the "normal" case first - VM_FAULT_MAJOR / VM_FAULT_MINOR
> --
> 1.7.5.4
>
--
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