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Wed, 9 Jun 2021 17:47:44 +0000 (GMT) Received: from oc7455500831.ibm.com (unknown [9.171.13.5]) by d06av26.portsmouth.uk.ibm.com (Postfix) with ESMTP; Wed, 9 Jun 2021 17:47:44 +0000 (GMT) Subject: Re: [PATCH v2 1/2] mm/vmalloc: export __vmalloc_node_range To: Claudio Imbrenda , Christoph Hellwig Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-s390@vger.kernel.org, frankja@linux.ibm.com, cohuck@redhat.com, david@redhat.com, linux-mm@kvack.org, Andrew Morton , Nicholas Piggin , Uladzislau Rezki , Catalin Marinas , Thomas Gleixner , Ingo Molnar , David Rientjes References: <20210608180618.477766-1-imbrenda@linux.ibm.com> <20210608180618.477766-2-imbrenda@linux.ibm.com> <20210609182809.7ae07aad@ibm-vm> From: Christian Borntraeger Message-ID: <6bf6fb06-0930-8cae-3e2b-8cb3237a6197@de.ibm.com> Date: Wed, 9 Jun 2021 19:47:43 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.0 MIME-Version: 1.0 In-Reply-To: <20210609182809.7ae07aad@ibm-vm> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: ZsdyWAcx_73hJwtXE9Sp0Mco4mrsan6t X-Proofpoint-GUID: qH6CxK9epqyjYop4gXKwm76Ys42u_HKD X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.391,18.0.761 definitions=2021-06-09_04:2021-06-04,2021-06-09 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 impostorscore=0 lowpriorityscore=0 mlxlogscore=999 adultscore=0 clxscore=1011 bulkscore=0 phishscore=0 spamscore=0 suspectscore=0 malwarescore=0 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2104190000 definitions=main-2106090087 X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 1BF806000145 X-Stat-Signature: tczuod7pfg61tf8ngxpp1eo8mi465ezx Authentication-Results: imf25.hostedemail.com; dkim=pass header.d=ibm.com header.s=pp1 header.b=GyE176Th; dmarc=pass (policy=none) header.from=ibm.com; spf=pass (imf25.hostedemail.com: domain of borntraeger@de.ibm.com designates 148.163.158.5 as permitted sender) smtp.mailfrom=borntraeger@de.ibm.com X-HE-Tag: 1623260880-112434 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 09.06.21 18:28, Claudio Imbrenda wrote: > On Wed, 9 Jun 2021 16:59:17 +0100 > Christoph Hellwig wrote: > >> On Tue, Jun 08, 2021 at 08:06:17PM +0200, Claudio Imbrenda wrote: >>> The recent patches to add support for hugepage vmalloc mappings >>> added a flag for __vmalloc_node_range to allow to request small >>> pages. This flag is not accessible when calling vmalloc, the only >>> option is to call directly __vmalloc_node_range, which is not >>> exported. >>> >>> This means that a module can't vmalloc memory with small pages. >>> >>> Case in point: KVM on s390x needs to vmalloc a large area, and it >>> needs to be mapped with small pages, because of a hardware >>> limitation. >>> >>> This patch exports __vmalloc_node_range so it can be used in modules >>> too. >> >> No. I spent a lot of effort to mak sure such a low-level API is >> not exported. > > ok, but then how can we vmalloc memory with small pages from KVM? An alternative would be to provide a vmalloc_no_huge function in generic code (similar to vmalloc_32) (or if preferred in s390 base architecture code) Something like void *vmalloc_no_huge(unsigned long size) { return __vmalloc_node_flags(size, NUMA_NO_NODE,VM_NO_HUGE_VMAP | GFP_KERNEL | __GFP_ZERO); } EXPORT_SYMBOL(vmalloc_no_huge); or a similar vzalloc variant.