On 21/03/2017 10:12, Aneesh Kumar K.V wrote: > Laurent Dufour <[email protected]> writes: > >> In do_page_fault() if handle_mm_fault() returns VM_FAULT_RETRY, retry >> the page fault handling before anything else. >> >> This would simplify the handling of the mmap_sem lock in this part of >> the code. >> >> Signed-off-by: Laurent Dufour <[email protected]> >> --- >> arch/powerpc/mm/fault.c | 67 >> ++++++++++++++++++++++++++++--------------------- >> 1 file changed, 38 insertions(+), 29 deletions(-) >> >> diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c >> index ee09604bbe12..2a6bc7e6e69a 100644 >> --- a/arch/powerpc/mm/fault.c >> +++ b/arch/powerpc/mm/fault.c >> @@ -434,6 +434,26 @@ int do_page_fault(struct pt_regs *regs, unsigned long >> address, >> * the fault. >> */ >> fault = handle_mm_fault(vma, address, flags); >> + >> + /* >> + * Handle the retry right now, the mmap_sem has been released in that >> + * case. >> + */ >> + if (unlikely(fault & VM_FAULT_RETRY)) { >> + /* We retry only once */ >> + if (flags & FAULT_FLAG_ALLOW_RETRY) { >> + /* >> + * Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk >> + * of starvation. >> + */ >> + flags &= ~FAULT_FLAG_ALLOW_RETRY; >> + flags |= FAULT_FLAG_TRIED; >> + if (!fatal_signal_pending(current)) >> + goto retry; >> + } >> + /* We will enter mm_fault_error() below */ >> + } >> + >> if (unlikely(fault & (VM_FAULT_RETRY|VM_FAULT_ERROR))) { >> if (fault & VM_FAULT_SIGSEGV) >> goto bad_area; >> @@ -445,38 +465,27 @@ int do_page_fault(struct pt_regs *regs, unsigned long >> address, >> } > > We could make it further simpler, by handling the FAULT_RETRY without > FLAG_ALLOW_RETRY set earlier. But i guess that can be done later ?
Thanks for the review, I agree that double checking against VM_FAULT_RETRY is confusing here. But handling all the retry path in the first if() statement means that we'll have to handle part of the mm_fault_error() code and segv here... Unless we can't identify what is really relevant in that retry path. It would take time to review all that tricky part, but I agree it should be simplified later. > > Reviewed-by: Aneesh Kumar K.V <[email protected]> > > >> >> /* >> - * 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. >> + * Major/minor page fault accounting. >> */ >> - if (flags & FAULT_FLAG_ALLOW_RETRY) { >> - if (fault & VM_FAULT_MAJOR) { >> - current->maj_flt++; >> - perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1, >> - regs, address); >> + if (fault & 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)) { >> - u32 page_ins; >> - >> - preempt_disable(); >> - page_ins = be32_to_cpu(get_lppaca()->page_ins); >> - page_ins += 1 << PAGE_FACTOR; >> - get_lppaca()->page_ins = cpu_to_be32(page_ins); >> - preempt_enable(); >> - } >> -#endif /* CONFIG_PPC_SMLPAR */ >> - } else { >> - current->min_flt++; >> - perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1, >> - regs, address); >> - } >> - if (fault & VM_FAULT_RETRY) { >> - /* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk >> - * of starvation. */ >> - flags &= ~FAULT_FLAG_ALLOW_RETRY; >> - flags |= FAULT_FLAG_TRIED; >> - goto retry; >> + if (firmware_has_feature(FW_FEATURE_CMO)) { >> + u32 page_ins; >> + >> + preempt_disable(); >> + page_ins = be32_to_cpu(get_lppaca()->page_ins); >> + page_ins += 1 << PAGE_FACTOR; >> + get_lppaca()->page_ins = cpu_to_be32(page_ins); >> + preempt_enable(); >> } >> +#endif /* CONFIG_PPC_SMLPAR */ >> + } else { >> + current->min_flt++; >> + perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1, >> + regs, address); >> } >> >> up_read(&mm->mmap_sem); >> -- >> 2.7.4
