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Wed, 29 Jul 2020 14:12:57 +0000 (GMT) Received: from linux.ibm.com (unknown [9.148.204.160]) by d06av26.portsmouth.uk.ibm.com (Postfix) with ESMTPS; Wed, 29 Jul 2020 14:12:57 +0000 (GMT) Date: Wed, 29 Jul 2020 17:12:54 +0300 From: Mike Rapoport To: David Hildenbrand Subject: Re: [RFC PATCH 0/6] decrease unnecessary gap due to pmem kmem alignment Message-ID: <20200729141254.GE3672596@linux.ibm.com> References: <20200729033424.2629-1-justin.he@arm.com> <20200729093150.GC3672596@linux.ibm.com> <20200729130025.GD3672596@linux.ibm.com> <170d7861-4df8-ecaf-dbdd-9e9a4a832f8f@redhat.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <170d7861-4df8-ecaf-dbdd-9e9a4a832f8f@redhat.com> X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235, 18.0.687 definitions=2020-07-29_07:2020-07-29, 2020-07-29 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 mlxscore=0 mlxlogscore=550 phishscore=0 malwarescore=0 lowpriorityscore=0 priorityscore=1501 suspectscore=0 spamscore=0 adultscore=0 bulkscore=0 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2007290091 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200729_101326_700029_E954F57B X-CRM114-Status: GOOD ( 21.46 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Kaly Xin , "Rafael J. Wysocki" , Catalin Marinas , Dave Hansen , "linux-mm@kvack.org" , Will Deacon , Justin He , "linux-nvdimm@lists.01.org" , Vishal Verma , Jason Gunthorpe , Kees Cook , Ira Weiny , Anshuman Khandual , Hsin-Yi Wang , Dave Jiang , Dan Williams , "linux-arm-kernel@lists.infradead.org" , Pankaj Gupta , Steve Capper , Greg Kroah-Hartman , "linux-kernel@vger.kernel.org" , Wei Yang , Andrew Morton , Logan Gunthorpe Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Jul 29, 2020 at 03:03:04PM +0200, David Hildenbrand wrote: > On 29.07.20 15:00, Mike Rapoport wrote: > > On Wed, Jul 29, 2020 at 11:35:20AM +0200, David Hildenbrand wrote: > >>> > >>> There is still large gap with ARM64_64K_PAGES, though. > >>> > >>> As for SPARSEMEM without VMEMMAP, are there actual benefits to use it? > >> > >> I was asking myself the same question a while ago and didn't really find > >> a compelling one. > > > > Memory overhead for VMEMMAP is larger, especially for arm64 that knows > > how to free empty parts of the memory map with "classic" SPARSEMEM. > > You mean the hole punching within section memmap? (which is why their > pfn_valid() implementation is special) Yes, arm (both 32 and 64) do this. And for smaller systems with a few memory banks this is very reasonable to trade slight (if any) slowdown in pfn_valid() for several megs of memory. > (I do wonder why that shouldn't work with VMEMMAP, or is it simply not > implemented?) It's not implemented. There was a patch [1] recently to implement this. [1] https://lore.kernel.org/lkml/20200721073203.107862-1-liwei213@huawei.com/ > -- > Thanks, > > David / dhildenb > -- Sincerely yours, Mike. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel