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    SubjectRe: [PATCH 04/20 v3] powerpc/mm/fault.c: Port OOM changes to do_page_fault
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    On Wed, 2012-03-21 at 08:28 +1100, Benjamin Herrenschmidt wrote:
    > 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....

    BTW. Feel free to review what I've done, it's quite possible that I have
    screwed something up ...

    Cheers,
    Ben.

    > 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;
    > >
    >




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