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From: "Aneesh Kumar K.V" Message-ID: Date: Mon, 17 May 2021 13:14:54 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: 8NTR7gbVZVmRTsV-q01Kmv5NdwaQNC_6 X-Proofpoint-ORIG-GUID: 8NTR7gbVZVmRTsV-q01Kmv5NdwaQNC_6 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.391, 18.0.761 definitions=2021-05-17_01:2021-05-12, 2021-05-17 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 mlxscore=0 lowpriorityscore=0 impostorscore=0 malwarescore=0 clxscore=1015 suspectscore=0 bulkscore=0 adultscore=0 priorityscore=1501 spamscore=0 mlxlogscore=999 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2104190000 definitions=main-2105170052 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On 5/17/21 12:55 PM, Anshuman Khandual wrote: > > > On 5/17/21 11:25 AM, Aneesh Kumar K.V wrote: >> On 5/17/21 11:17 AM, Christophe Leroy wrote: >>> +aneesh >>> +linuxppc-dev list >>> >>> Le 17/05/2021 à 07:44, Anshuman Khandual a écrit : >>>> Hello Christophe, >>>> >>>> DEBUG_VM_PGTABLE has now been re-enabled on powerpc recently ? was not >>>> aware about this. From the error log, it failed explicitly on 4K page >>>> size hash config. >>>> >>>> static inline pmd_t hash__pmd_mkhuge(pmd_t pmd) >>>> { >>>> BUG(); ------> Failed >>>> return pmd; >>>> } >>>> >>>> static inline pmd_t __pmd_mkhuge(pmd_t pmd) >>>> { >>>> if (radix_enabled()) >>>> return radix__pmd_mkhuge(pmd); >>>> return hash__pmd_mkhuge(pmd); >>>> } >>>> >>>> pmd_t pfn_pmd(unsigned long pfn, pgprot_t pgprot) >>>> { >>>> unsigned long pmdv; >>>> >>>> pmdv = (pfn << PAGE_SHIFT) & PTE_RPN_MASK; >>>> >>>> return __pmd_mkhuge(pmd_set_protbits(__pmd(pmdv), pgprot)); >>>> } >>>> >>>> It seems like on powerpc, where pfn_pmd() makes a huge page but which >>>> is not supported on 4K hash config thus triggering the BUG(). But all >>>> pfn_pmd() call sites inside the debug_vm_pgtable() test are protected >>>> with CONFIG_TRANSPARENT_HUGEPAGE. IIUC unlike powerpc, pfn_pmd() does >>>> not directly make a huge page on other platforms. >>>> >>>> Looking at arch/powerpc/include/asm/book3s/64/hash-4k.h, all relevant >>>> THP helpers has BUG() or 0 which indicates THP might not be supported >>>> on 4K page size hash config ? >>>> >>>> But looking at arch/powerpc/platforms/Kconfig.cputype, it seems like >>>> HAVE_ARCH_TRANSPARENT_HUGEPAGE is invariably selected on PPC_BOOK3S_64 >>>> platforms which I assume includes 4K page size hash config as well. >>>> >>>> Is THP some how getting enabled on this 4K page size hash config where >>>> it should not be (thus triggering the BUG) ? OR am I missing something >>>> here. >>>> >>> >> >> We should put those pfn_pmd() and pfn_pud() after >> >> if (!has_transparent_hugepage()) >> return; >> >> >> On hash with 4K page size, we can't support leaf page table entry and PMD and PUD level. Hence we don't support THP for them. > > But could CONFIG_TRANSPARENT_HUGEPAGE be enabled on such configs ? > Otherwise, wondering how the BUG() just got triggered there. > yes. We do support THP with radix translation and 4K page size. -aneesh