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dkim=pass header.d=fb.com header.s=facebook header.b=n57rw0Oe; dmarc=pass (policy=reject) header.from=fb.com; spf=none (imf26.hostedemail.com: domain of "prvs=5094d560ed=songliubraving@fb.com" has no SPF policy when checking 67.231.153.30) smtp.mailfrom="prvs=5094d560ed=songliubraving@fb.com" X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 83B73140021 X-HE-Tag: 1649202928-513378 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: > 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 strate= gy.=20 >> IIUC, most of the kernel is not ready for huge page backed vmalloc memor= y. >> For example, all the module_alloc cannot work with huge pages at the mom= ent. >> 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 page= s.=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. Nicholas and Claudio,=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 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