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Thu, 6 Nov 2025 16:37:58 +0000 (GMT) Message-ID: <95a76871-771a-4fac-9771-c9e1f4a888ea@de.ibm.com> Date: Thu, 6 Nov 2025 17:37:57 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 21/23] KVM: s390: Enable 1M pages for gmap To: Claudio Imbrenda Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, frankja@linux.ibm.com, nsg@linux.ibm.com, nrb@linux.ibm.com, seiden@linux.ibm.com, schlameuss@linux.ibm.com, hca@linux.ibm.com, svens@linux.ibm.com, agordeev@linux.ibm.com, gor@linux.ibm.com, david@redhat.com, gerald.schaefer@linux.ibm.com References: <20251106161117.350395-1-imbrenda@linux.ibm.com> <20251106161117.350395-22-imbrenda@linux.ibm.com> <5dd6e694-8cf9-4b1c-ae83-088b6bd22a17@de.ibm.com> <20251106173650.31907261@p-imbrenda> Content-Language: en-US From: Christian Borntraeger In-Reply-To: <20251106173650.31907261@p-imbrenda> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=StmdKfO0 c=1 sm=1 tr=0 ts=690cceeb cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=IkcTkHD0fZMA:10 a=6UeiqGixMTsA:10 a=VkNPw1HP01LnGYTKEx00:22 a=VnNF1IyMAAAA:8 a=5sJ8VKY1vcdsYsRJmOUA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-ORIG-GUID: Dxoqecpu3TmIX9REChJRyfO3QtVplp-3 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMTAxMDAxOCBTYWx0ZWRfX3LmNWjF9h0IQ EGv+27rIKyfOfjobr7eDaySxCX8Vicm6hHee4KW+Ke9HukAqpi+/rOJpJVrLmOmaEALiVBxi6BF mJ/82fD072gWkhQ9rfxEb/7HU5ui7lgEsPxzpVYjGyvGktLG7HiPYB1lIC9FjXoIIEVv4KiHwEP wdN6Hjt7J7jLIQ0QS8cMYmd/8toGfvcrddeQiiavtx02fjdNT49FTCdnO+PmLp40GyZmHZN+rkM J/f/8SqADtWPn1QsOUwMcXJ0X6l+eDoYYONC0jBUHHzVtu1Su4IbW3UIjLuI8P4+d9P3I1JYoGA bAnUIvlpa6A1CNbekzNcPN0ZapiXcFd5iAZxHOArQNEVqgXO7kuXubrsRDxFyceJYg/Sq7+YHWO TwvmxLya2R3NPTVhjDz2uJ5rlbwRRg== X-Proofpoint-GUID: Dxoqecpu3TmIX9REChJRyfO3QtVplp-3 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.100.49 definitions=2025-11-06_03,2025-11-06_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 phishscore=0 impostorscore=0 priorityscore=1501 malwarescore=0 clxscore=1015 adultscore=0 bulkscore=0 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2510240000 definitions=main-2511010018 Am 06.11.25 um 17:36 schrieb Claudio Imbrenda: > On Thu, 6 Nov 2025 17:22:33 +0100 > Christian Borntraeger wrote: > >> Am 06.11.25 um 17:11 schrieb Claudio Imbrenda: >>> While userspace is allowed to have pages of any size, the new gmap >>> would always use 4k pages to back the guest. >>> >>> Enable 1M pages for gmap. >>> >>> This allows 1M pages to be used to back a guest when userspace is using >>> 1M pages for the corresponding addresses (e.g. THP or hugetlbfs). >>> >>> Remove the limitation that disallowed having nested guests and >>> hugepages at the same time. >> >> Nice. This might allow us to enable hpage=1 as new default as soon as >> things stabilize. >> >> We would also be able to use 2GB huge pages for the qemu mapping? > > yes, but I don't think that userspace can have 2G THPs right now Not THP, but hugetlbfs.