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Mon, 30 May 2022 18:29:34 GMT Received: from d06av21.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 12CBA5204F; Mon, 30 May 2022 18:29:34 +0000 (GMT) Received: from [9.171.42.121] (unknown [9.171.42.121]) by d06av21.portsmouth.uk.ibm.com (Postfix) with ESMTP id D9F875204E; Mon, 30 May 2022 18:29:30 +0000 (GMT) Message-ID: <58b163b1-22ec-7634-dcd3-5a0a54adec45@linux.ibm.com> Date: Mon, 30 May 2022 20:29:30 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.8.0 Subject: Re: [PATCH v4] mm: Avoid unnecessary page fault retires on shared memory types Content-Language: en-US To: Peter Xu Cc: Heiko Carstens , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Will Deacon , Matt Turner , linux-s390@vger.kernel.org, Andrew Morton , Brian Cain , Borislav Petkov , linux-alpha@vger.kernel.org, Alistair Popple , Jonas Bonn , linux-arm-kernel@lists.infradead.org, linux-ia64@vger.kernel.org, Michael Ellerman , Stefan Kristiansson , linux-snps-arc@lists.infradead.org, Vineet Gupta , Vasily Gorbik , Vlastimil Babka , Ivan Kokshaysky , Rich Felker , sparclinux@vger.kernel.org, Russell King , David Hildenbrand , Benjamin Herrenschmidt , Nicholas Piggin , "James E . J . Bottomley" , linux-xtensa@linux-xtensa.org, linux-sh@vger.kernel.org, Paul Walmsley , linux-m68k@lists.linux-m68k.org, linuxppc-dev@lists.ozlabs.org, Richard Henderson , Guo Ren , linux-parisc@vger.kernel.org, Andrea Arcangeli , Helge Deller , Al Viro , Albert Ou , linux-um@lists.infradead.org, "H . Peter Anvin" , Janosch Frank , Sven Schnelle , Anton Ivanov , openrisc@lists.librecores.org, Thomas Bogendoerfer , linux-hexagon@vger.kernel.org, Andy Lutomirski , Stafford Horne , linux-csky@vger.kernel.org, Thomas Gleixner , linux-mips@vger.kernel.org, Paul Mackerras , Alexander Gordeev , Dinh Nguyen , Palmer Dabbelt , "David S . Miller" , Johannes Weiner , Hugh Dickins , Ingo Molnar , Peter Zijlstra , linux-riscv@lists.infradead.org, Max Filippov , Catalin Marinas , Geert Uytterhoeven , Johannes Berg , Chris Zankel , Michal Simek , x86@kernel.org, Yoshinori Sato , Dave Hansen , Richard Weinberger , Ingo Molnar References: <20220527193936.30678-1-peterx@redhat.com> <33fd4731-9765-d78b-bdc3-f8243c98e81f@linux.ibm.com> From: Christian Borntraeger In-Reply-To: X-TM-AS-GCONF: 00 X-Proofpoint-GUID: BcnqcIajExbqAnGujS-ZUqcYMX48oxDt X-Proofpoint-ORIG-GUID: iK5fU7K0gq48iA5OulnJebFyFFDVydua X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.874,Hydra:6.0.517,FMLib:17.11.64.514 definitions=2022-05-30_07,2022-05-30_03,2022-02-23_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 mlxscore=0 lowpriorityscore=0 priorityscore=1501 phishscore=0 suspectscore=0 adultscore=0 malwarescore=0 impostorscore=0 spamscore=0 mlxlogscore=999 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2204290000 definitions=main-2205300096 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220530_112955_298424_78E705FB X-CRM114-Status: GOOD ( 24.09 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org Am 30.05.22 um 18:00 schrieb Peter Xu: > On Mon, May 30, 2022 at 11:52:54AM -0400, Peter Xu wrote: >> On Mon, May 30, 2022 at 11:35:10AM +0200, Christian Borntraeger wrote: >>> >>> >>> Am 29.05.22 um 22:33 schrieb Heiko Carstens: >>> [...] >>>> >>>> Guess the patch below on top of your patch is what we want. >>>> Just for clarification: if gmap is not NULL then the process is a kvm >>>> process. So, depending on the workload, this optimization makes sense. >>>> >>>> diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c >>>> index 4608cc962ecf..e1d40ca341b7 100644 >>>> --- a/arch/s390/mm/fault.c >>>> +++ b/arch/s390/mm/fault.c >>>> @@ -436,12 +436,11 @@ static inline vm_fault_t do_exception(struct pt_regs *regs, int access) >>>> /* The fault is fully completed (including releasing mmap lock) */ >>>> if (fault & VM_FAULT_COMPLETED) { >>>> - /* >>>> - * Gmap will need the mmap lock again, so retake it. TODO: >>>> - * only conditionally take the lock when CONFIG_PGSTE set. >>>> - */ >>>> - mmap_read_lock(mm); >>>> - goto out_gmap; >>>> + if (gmap) { >>>> + mmap_read_lock(mm); >>>> + goto out_gmap; >>>> + } >>>> + goto out; > > Hmm, right after I replied I found "goto out" could be problematic, since > all s390 callers of do_exception() will assume it an error condition (side > note: "goto out_gmap" contains one step to clear "fault" to 0). I'll > replace this with "return 0" instead if it looks good to both of you. > > I'll wait for a confirmation before reposting. Thanks, Yes, that sounds good and thank you for double checking. _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv