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Wed, 21 Oct 2026 14:07:56 +0000 (GMT) Received: from fedora (unknown [9.5.7.39]) by smtpav04.fra02v.mail.ibm.com (Postfix) with ESMTPS; Wed, 21 Oct 2026 14:07:56 +0000 (GMT) Date: Wed, 21 Oct 2026 19:46:21 +0530 From: Amit Machhiwal To: Michal =?utf-8?B?U3VjaMOhbmVr?= Cc: Amit Machhiwal , Steven Rostedt , Masami Hiramatsu , linux-trace-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, Vincent Donnefort , Mathieu Desnoyers , Madhavan Srinivasan , "Ritesh Harjani (IBM)" , Harsh Prateek Bora , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, kvm-ppc@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH v2] ring-buffer: Do not check si_mem_available() before deferred init completes Message-ID: <20261021194442.d82d52ff-07-amachhiw@linux.ibm.com> Mail-Followup-To: Michal =?utf-8?B?U3VjaMOhbmVr?= , Steven Rostedt , Masami Hiramatsu , linux-trace-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, Vincent Donnefort , Mathieu Desnoyers , Madhavan Srinivasan , "Ritesh Harjani (IBM)" , Harsh Prateek Bora , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, kvm-ppc@vger.kernel.org, stable@vger.kernel.org References: <20261009163557.88467-3-amachhiw@linux.ibm.com> <20261016134247.70722-1-amachhiw@linux.ibm.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYxMDIxMDA1NCBTYWx0ZWRfXyG65JXecQ1qZ XTrj6qOaw599HABgWv3Eww0Xs9tLyqxfAKHoR+2McAqaVtBYvr3IrTcJrbmkMlRuUQuvANACUEW 7IluMJcNfVuTpkOTRtuMf6laDL8JULOhPdDV76eGJDCcMKAAG0fDCtg9tMFNgqghXzkEWHxq5ae xU5BARihXwnoT4+ZbGcX7OPy87xGLE1RuVu5/FunFdVpRq35lxYeolBGPNTEfTUSU9irEmVea1C a5qm55uFNWYwqMcg0WUh7smrsVRv2mIjQLTTsNjaCjOeIM1NHVy/PUgMm6LHastdF8ZKU0flIuk +CwOXDrwyy28c5fVpnBIu+iqrz5aRN6NkMnUgLRafIzE5dkj4h7LGugRrljWdlTfkSfunDJskEI qRIr4PWFC5q7t/MwLeEpKWnGC/mxmhtGJEThA/flhxLEvBV1Ujf894BzFFnj1I4kJrDvlIU3fkn XvlmDwAbfn+AIjd93GA== X-Proofpoint-ORIG-GUID: hyUw3X5wNZrdxkXQRgY-MffWMIOFZAJT X-Proofpoint-GUID: KO4BRUAyOt7JDDy1mg87zV7Y6gkDWO3B X-Proofpoint-Spam-Info: AW1haW4tMjYxMDIxMDA1NCBTYWx0ZWRfX8uqSMDpxuI6A J8xRgCnNYesbvsgxGa0BeU2aPp1OqIHPJasPEANYOfB6h98yFst7I5eeh2JXUc3yxHAKO+6G9Tu fFH9RfJll9qgCA8BfNMPMFUZ2ipTKoE= X-Authority-Analysis: v=2.4 cv=ZfSIpcVA c=1 sm=1 tr=0 ts=6ad8c747 cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=8nJEP1OIZ-IA:10 a=660iZSQnnn4A:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=RzCfie-kr_QcCd8fBx8p:22 a=M0V5yE8pmHsQCC-Gis0A:9 a=3ZKOabzyN94A:10 a=wPNLvfGTeEIA:10 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.138,FMLib:17.12.100.49 definitions=2026-10-21_03,2026-10-21_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 impostorscore=0 malwarescore=0 spamscore=0 suspectscore=0 clxscore=1015 phishscore=0 bulkscore=0 lowpriorityscore=0 adultscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2610190000 definitions=main-2610210054 On 2026/10/19 12:57 PM, Michal Suchánek wrote: > On Fri, Oct 16, 2026 at 07:12:47PM +0530, Amit Machhiwal wrote: > > During early boot (early_trace_init() called from start_kernel()), > > tracing allocates initial ring buffers (temp_buffer, array_buffer, and > > snapshot_buffer) for CPU 0. Later, as secondary CPUs come online during > > smp_init(), each CPU's ring buffer is allocated via trace_rb_cpu_prepare(). > > > > Before attempting page allocation, __rb_allocate_pages() performs a > > heuristic check using si_mem_available() to return early with -ENOMEM if > > memory appears insufficient. > > > > kernel/trace/ring_buffer.c | 14 ++++++++++++++ > > 1 file changed, 14 insertions(+) > > > > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c > > index 04bb94c29f58..aa877a272c89 100644 > > --- a/kernel/trace/ring_buffer.c > > +++ b/kernel/trace/ring_buffer.c > > @@ -2452,10 +2452,24 @@ static int __rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer, > > * memory. It may not be accurate. But we don't care, we just want > > * to prevent doing any allocation when it is obvious that it is > > * not going to succeed. > > + * > > + * With CONFIG_DEFERRED_STRUCT_PAGE_INIT, NR_FREE_PAGES only reflects > > + * the initial non-deferred pool during early boot and throughout SMP > > + * bring-up (smp_init() runs before page_alloc_init_late() completes > > + * deferred initialization). si_mem_available() returns a false negative > > + * across this entire window while actual allocations succeed by growing > > + * the zone on demand via deferred_grow_zone(). Only re-enable the check > > + * from SYSTEM_FREEING_INITMEM onward, after page_alloc_init_late() has > > + * finished and si_mem_available() is accurate. > > */ > > i = si_mem_available(); > > +#ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT > > + if (system_state >= SYSTEM_FREEING_INITMEM && i < nr_pages) > > + return -ENOMEM; > > +#else > > if (i < nr_pages) > > return -ENOMEM; > > +#endif > > > > /* > > * If a user thread allocates too much, and si_mem_available() > > > > base-commit: 2f2f7eeef8b0a1a9b9ca998231419873ccae8d4e > > Hello, > > due to other conflicting changes this no longer applies. > > Will you send a rebase? Hi Michal, Thanks for checking and notifying. I'll look into it and send a v3 as needed. Thanks, Amit