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Wed, 17 Sep 2025 12:12:11 +0000 (GMT) Date: Wed, 17 Sep 2025 14:12:09 +0200 From: Claudio Imbrenda To: Heiko Carstens Cc: Christian Borntraeger , kvm@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, svens@linux.ibm.com, agordeev@linux.ibm.com, david@redhat.com, gerald.schaefer@linux.ibm.com Subject: Re: [PATCH v2 08/20] KVM: s390: KVM page table management functions: allocation Message-ID: <20250917141209.377a05aa@p-imbrenda> In-Reply-To: <20250916173644.27229Kcc-hca@linux.ibm.com> References: <20250910180746.125776-1-imbrenda@linux.ibm.com> <20250910180746.125776-9-imbrenda@linux.ibm.com> <20250916162653.27229G04-hca@linux.ibm.com> <20250916184737.47224f56@p-imbrenda> <63e8c905-28b1-4e1f-be77-e0789bd75692@de.ibm.com> <20250916190514.1a3082bd@p-imbrenda> <15f451d9-ecb3-4a82-9b9a-2de64b93944d@de.ibm.com> <20250916173644.27229Kcc-hca@linux.ibm.com> Organization: IBM X-Mailer: Claws Mail 4.3.1 (GTK 3.24.49; x86_64-redhat-linux-gnu) Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwOTE2MDIwNCBTYWx0ZWRfX9NDipppFPFFM JnZk1PUH7zG9niKR4MewqU7qdacMKQEhb6wZNH4rnwhAf9lO9+bFX9p98pYpEU8QB6dvgErPfqm /APL8lz+Xk87cPzEYOU5rHI0llkAmQshszOFU0nUTygZaXn/kjB6mMZoaCAgt0ne8ijMfqAHJN0 l1mYxfiHGAa5GW7VU6IHnPk7qOnxgKkqMQUErTw+gf9tuooZTD/YDx+OVYUZ3ATsfzmEr8h0oF1 P1hDHTNhVOvrcDYq+Auc+ml47mSeQhPN9QaF0MnX/IvyIBZHuagq13irrXpUI23Bgom2acyUdh4 rUcHha2UGQ6iFwuAPxqFmujDPgC8ruz2zSNfBR3663PFWY15KvFyQTh7gjLSCok4M13S5Vd61se gt0S8zC/ X-Proofpoint-ORIG-GUID: EYQUKlSnyC2_83UsxatAWFB_qtgRGLJR X-Proofpoint-GUID: EYQUKlSnyC2_83UsxatAWFB_qtgRGLJR X-Authority-Analysis: v=2.4 cv=cNzgskeN c=1 sm=1 tr=0 ts=68caa5a0 cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==:17 a=kj9zAlcOel0A:10 a=yJojWOMRYYMA:10 a=07d9gI8wAAAA:8 a=VnNF1IyMAAAA:8 a=ifL_N-yr7MKzoRw6B2EA:9 a=CjuIK1q_8ugA:10 a=e2CUPOnPG4QKp8I52DXD:22 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1117,Hydra:6.1.9,FMLib:17.12.80.40 definitions=2025-09-17_01,2025-09-17_01,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 clxscore=1015 spamscore=0 bulkscore=0 malwarescore=0 adultscore=0 priorityscore=1501 impostorscore=0 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2507300000 definitions=main-2509160204 On Tue, 16 Sep 2025 19:36:44 +0200 Heiko Carstens wrote: > On Tue, Sep 16, 2025 at 07:06:06PM +0200, Christian Borntraeger wrote: > > > > Am 16.09.25 um 19:05 schrieb Claudio Imbrenda: > > > > > > > I think GFP_ATOMIC actually gives more guarantees? > > > > > > > > In real life GFP_ATOMIC can fail, GFP_KERNEL does not.All gfp allocation failures > > > > are usually the atomic ones. > > > > > > interesting... then I guess I need GFP_KERNEL | GFP_ATOMIC ? > > > > No. ATOMIC always means: can fail. > > So GFP_KERNEL alone is what is needed here. It is undocumented that > small GFP_KERNEL allocations will never fail (retried for ever): > > https://lwn.net/Articles/627419/ > https://lwn.net/Articles/723317/ > > While GFP_ATOMIC will fail e.g. if I/O is required to free up some > memory. ah, "how small is small" is answered in those links, ignore my question