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Thu, 6 Nov 2025 16:22:33 +0000 (GMT) Message-ID: <5dd6e694-8cf9-4b1c-ae83-088b6bd22a17@de.ibm.com> Date: Thu, 6 Nov 2025 17:22:33 +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 , kvm@vger.kernel.org Cc: 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> Content-Language: en-US From: Christian Borntraeger In-Reply-To: <20251106161117.350395-22-imbrenda@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: c46-cRktUHCAobPYCSnH0_UD5Kf9bEq7 X-Authority-Analysis: v=2.4 cv=MKhtWcZl c=1 sm=1 tr=0 ts=690ccb4f cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=IkcTkHD0fZMA:10 a=6UeiqGixMTsA:10 a=VkNPw1HP01LnGYTKEx00:22 a=6ItpLjnqAre2Uv_fE_cA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-ORIG-GUID: c46-cRktUHCAobPYCSnH0_UD5Kf9bEq7 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMTAxMDAwMSBTYWx0ZWRfXxScOihMx6Gr+ Qxxdn0Jpaak/ZRrvchASrb7hMX4elhK0ZQthGg8B01dkAJ4ivK5U+w+llbd3cqhxgtiefA0pTGr y5csPfqS5ZccKsRIBX2cFF8sFBWBw/UuZUI0zio8IcS+OtHGkiQxcpLlkPRpk4pAxmtpRP0xVQS xisdBp+/eMfEKoOgQPBDpeB06DR3I0VGRtwXCgBS7gPJ6m6jSYXEaMqlYdwqvLg2P7VLY83gin/ 0+H4dggPVzW7AlWa9imhlJHYkhZhpUlPVFufhwD6lboMrcA1fykRFYskUeRM77zPfYGqqDDm9xz LLVvU+/tj6kYzA7F4JXB4bvXQq5qSS7Bt3FnCm9ctdz8oOFksZw91hLxLbWx4sTI4QzD3N/sjEK qKZCKH2uOBoSHmXtXdrZVq04M/vxJA== 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 priorityscore=1501 suspectscore=0 bulkscore=0 impostorscore=0 clxscore=1011 lowpriorityscore=0 malwarescore=0 adultscore=0 phishscore=0 spamscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2510240000 definitions=main-2511010001 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? With this patch we then have 1MB pages for the guest mapping. As a future improvement, maybe also allow guest mapping 2GB pages.