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dkim=pass header.d=fb.com header.s=facebook header.b=cg4mIjMD; spf=none (imf07.hostedemail.com: domain of "prvs=5096605e4a=songliubraving@fb.com" has no SPF policy when checking 67.231.145.42) smtp.mailfrom="prvs=5096605e4a=songliubraving@fb.com"; dmarc=pass (policy=reject) header.from=fb.com X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: EEF1C40005 X-HE-Tag: 1649361504-608449 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Hi Nicholas and Claudio,=20 > On Apr 5, 2022, at 4:54 PM, Song Liu wrote: >=20 >> On Apr 5, 2022, at 12:07 AM, Christoph Hellwig wrote= : >>=20 >> 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. >>>=20 >>> After reading the code a little more, I wonder what would be best strat= egy.=20 >>> IIUC, most of the kernel is not ready for huge page backed vmalloc memo= ry. >>> For example, all the module_alloc cannot work with huge pages at the mo= ment. >>> And the error Paul Menzel reported in drm_fb_helper.c will probably hit= =20 >>> powerpc with 5.17 kernel as-is? (trace attached below)=20 >>>=20 >>> Right now, we have VM_NO_HUGE_VMAP to let a user to opt out of huge pag= es.=20 >>> However, given there are so many users of vmalloc, vzalloc, etc., we=20 >>> probably do need a flag for the user to opt-in?=20 >>>=20 >>> Does this make sense? Any recommendations are really appreciated.=20 >>=20 >> I think there is multiple aspects here: >>=20 >> - if we think that the kernel is not ready for hugepage backed vmalloc >> in general we need to disable it in powerpc for now. >=20 > Nicholas and Claudio,=20 >=20 > What do you think about the status of hugepage backed vmalloc on powerpc?= =20 > 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=20 > current opt-out flag, VM_NO_HUGE_VMAP) make sense to you?=20 Could you please share your comments on this? Specifically, does it make=20 sense to replace VM_NO_HUGE_VMAP with an opt-in flag? If we think current opt-out flag is better approach, what would be the best practice to find=20 all the cases to opt-out? Thanks, Song > Thanks, > Song >=20 >> - 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 >=20