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charset="us-ascii" Content-ID: <8CA306781FF3BD43BD81B09631D0720C@namprd15.prod.outlook.com> MIME-Version: 1.0 X-OriginatorOrg: fb.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: SA1PR15MB5109.namprd15.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 514ea588-ac1c-49ce-153a-08da175fa4b2 X-MS-Exchange-CrossTenant-originalarrivaltime: 05 Apr 2022 23:54:37.7719 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: v06S8TU81pBk7B0RCnJHDYKlsVYkiVph4xrPUdExd2Qva78ZwaD6AXtOiAppw24qFA+zICsKHtL0rVwFXewnbQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM5PR15MB1804 X-Proofpoint-ORIG-GUID: GgN7tVFU65_vh8wVEdt3TOX7gnwKIl-S X-Proofpoint-GUID: GgN7tVFU65_vh8wVEdt3TOX7gnwKIl-S X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.850,Hydra:6.0.425,FMLib:17.11.64.514 definitions=2022-04-05_08,2022-04-05_01,2022-02-23_01 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org > On Apr 5, 2022, at 12:07 AM, Christoph Hellwig wrote: > > On Fri, Apr 01, 2022 at 10:22:00PM +0000, Song Liu wrote: >>>> Please fix the underlying issues instead of papering over them and >>>> creating a huge maintainance burden for others. >> >> After reading the code a little more, I wonder what would be best strategy. >> IIUC, most of the kernel is not ready for huge page backed vmalloc memory. >> For example, all the module_alloc cannot work with huge pages at the moment. >> And the error Paul Menzel reported in drm_fb_helper.c will probably hit >> powerpc with 5.17 kernel as-is? (trace attached below) >> >> Right now, we have VM_NO_HUGE_VMAP to let a user to opt out of huge pages. >> However, given there are so many users of vmalloc, vzalloc, etc., we >> probably do need a flag for the user to opt-in? >> >> Does this make sense? Any recommendations are really appreciated. > > I think there is multiple aspects here: > > - if we think that the kernel is not ready for hugepage backed vmalloc > in general we need to disable it in powerpc for now. Nicholas and Claudio, What do you think about the status of hugepage backed vmalloc on powerpc? I found module_alloc and kvm_s390_pv_alloc_vm() opt-out of huge pages. But I am not aware of users that benefit from huge pages (except vfs hash, which was mentioned in 8abddd968a30). Does an opt-in flag (instead of current opt-out flag, VM_NO_HUGE_VMAP) make sense to you? Thanks, Song > - if we think even in the longer run only some users can cope with > hugepage backed vmalloc we need to turn it into an opt-in in > general and not just for x86 > - there still to appear various unresolved underlying x86 specific > issues that need to be fixed either way