Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751840AbdHUG7s (ORCPT ); Mon, 21 Aug 2017 02:59:48 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:53445 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751088AbdHUG7q (ORCPT ); Mon, 21 Aug 2017 02:59:46 -0400 Subject: Re: [PATCH v2 20/20] powerpc/mm: Add speculative page fault To: Laurent Dufour , paulmck@linux.vnet.ibm.com, peterz@infradead.org, akpm@linux-foundation.org, kirill@shutemov.name, ak@linux.intel.com, mhocko@kernel.org, dave@stgolabs.net, jack@suse.cz, Matthew Wilcox , benh@kernel.crashing.org, mpe@ellerman.id.au, paulus@samba.org, Thomas Gleixner , Ingo Molnar , hpa@zytor.com, Will Deacon References: <1503007519-26777-1-git-send-email-ldufour@linux.vnet.ibm.com> <1503007519-26777-21-git-send-email-ldufour@linux.vnet.ibm.com> Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, haren@linux.vnet.ibm.com, khandual@linux.vnet.ibm.com, npiggin@gmail.com, bsingharora@gmail.com, Tim Chen , linuxppc-dev@lists.ozlabs.org, x86@kernel.org From: Anshuman Khandual Date: Mon, 21 Aug 2017 12:28:46 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1 MIME-Version: 1.0 In-Reply-To: <1503007519-26777-21-git-send-email-ldufour@linux.vnet.ibm.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable x-cbid: 17082106-0004-0000-0000-0000022B2DAB X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17082106-0005-0000-0000-00005E12076C Message-Id: X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-08-21_05:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1707230000 definitions=main-1708210111 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3247 Lines: 93 On 08/18/2017 03:35 AM, Laurent Dufour wrote: > This patch enable the speculative page fault on the PowerPC > architecture. > > This will try a speculative page fault without holding the mmap_sem, > if it returns with WM_FAULT_RETRY, the mmap_sem is acquired and the s/WM_FAULT_RETRY/VM_FAULT_RETRY/ > traditional page fault processing is done. > > Support is only provide for BOOK3S_64 currently because: > - require CONFIG_PPC_STD_MMU because checks done in > set_access_flags_filter() What checks are done in set_access_flags_filter() ? We are just adding the code block in do_page_fault(). > - require BOOK3S because we can't support for book3e_hugetlb_preload() > called by update_mmu_cache() > > Signed-off-by: Laurent Dufour > --- > arch/powerpc/include/asm/book3s/64/pgtable.h | 5 +++++ > arch/powerpc/mm/fault.c | 30 +++++++++++++++++++++++++++- > 2 files changed, 34 insertions(+), 1 deletion(-) > > diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h > index 818a58fc3f4f..897f8b9f67e6 100644 > --- a/arch/powerpc/include/asm/book3s/64/pgtable.h > +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h > @@ -313,6 +313,11 @@ extern unsigned long pci_io_base; > /* Advertise support for _PAGE_SPECIAL */ > #define __HAVE_ARCH_PTE_SPECIAL > > +/* Advertise that we call the Speculative Page Fault handler */ > +#if defined(CONFIG_PPC_BOOK3S_64) > +#define __HAVE_ARCH_CALL_SPF > +#endif > + > #ifndef __ASSEMBLY__ > > /* > diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c > index 4c422632047b..7b3cc4c30eab 100644 > --- a/arch/powerpc/mm/fault.c > +++ b/arch/powerpc/mm/fault.c > @@ -291,9 +291,36 @@ int do_page_fault(struct pt_regs *regs, unsigned long address, > if (is_write && is_user) > store_update_sp = store_updates_sp(regs); > > - if (is_user) > + if (is_user) { > flags |= FAULT_FLAG_USER; > > +#if defined(__HAVE_ARCH_CALL_SPF) > + /* let's try a speculative page fault without grabbing the > + * mmap_sem. > + */ > + > + /* > + * flags is set later based on the VMA's flags, for the common > + * speculative service, we need some flags to be set. > + */ > + if (is_write) > + flags |= FAULT_FLAG_WRITE; > + > + fault = handle_speculative_fault(mm, address, flags); > + if (!(fault & VM_FAULT_RETRY || fault & VM_FAULT_ERROR)) { > + perf_sw_event(PERF_COUNT_SW_SPF_DONE, 1, > + regs, address); > + goto done; Why we should retry with classical page fault on VM_FAULT_ERROR ? We should always return VM_FAULT_RETRY in case there is a clear collision some where which requires retry with classical method and return VM_FAULT_ERROR in cases where we know that it cannot be retried and fail for good. Should not handle_speculative_fault() be changed to accommodate this ? > + } > + > + /* > + * Resetting flags since the following code assumes > + * FAULT_FLAG_WRITE is not set. > + */ > + flags &= ~FAULT_FLAG_WRITE; > +#endif /* defined(__HAVE_ARCH_CALL_SPF) */ Setting and resetting of FAULT_FLAG_WRITE seems confusing. Why you say that some flags need to be set for handle_speculative_fault() function. Could you elaborate on this ?