On 7/17/20 2:51 AM, Anshuman Khandual wrote: > > > On 07/17/2020 02:06 PM, Will Deacon wrote: >> On Fri, Jul 17, 2020 at 10:32:53AM +0530, Anshuman Khandual wrote: >>> >>> >>> On 07/16/2020 11:55 PM, Mike Kravetz wrote: >>>> >From 17c8f37afbf42fe7412e6eebb3619c6e0b7e1c3c Mon Sep 17 00:00:00 2001 >>>> From: Mike Kravetz <mike.kravetz@xxxxxxxxxx> >>>> Date: Tue, 14 Jul 2020 15:54:46 -0700 >>>> Subject: [PATCH] hugetlb: move cma reservation to code setting up gigantic >>>> hstate >>>> >>>> Instead of calling hugetlb_cma_reserve() directly from arch specific >>>> code, call from hugetlb_add_hstate when adding a gigantic hstate. >>>> hugetlb_add_hstate is either called from arch specific huge page setup, >>>> or as the result of hugetlb command line processing. In either case, >>>> this is late enough in the init process that all numa memory information >>>> should be initialized. And, it is early enough to still use early >>>> memory allocator. >>> >>> This assumes that hugetlb_add_hstate() is called from the arch code at >>> the right point in time for the generic HugeTLB to do the required CMA >>> reservation which is not ideal. I guess it must have been a reason why >>> CMA reservation should always called by the platform code which knows >>> the boot sequence timing better. >> >> Ha, except we've moved it around two or three times already in the last >> month or so, so I'd say we don't have a clue when to call it in the arch >> code. > > The arch dependency is not going way with this change either. Just that > its getting transferred to hugetlb_add_hstate() which gets called from > arch_initcall() in every architecture. > > The perfect timing here happens to be because of arch_initcall() instead. > This is probably fine, as long as > > 0. hugetlb_add_hstate() is always called at arch_initcall() In another reply, I give reasoning why it would be safe to call even later at hugetlb command line processing time. > 1. N_MEMORY mask is guaranteed to be initialized at arch_initcall() This is a bit more difficult to guarantee. I find the init sequence hard to understand. Looking at the arm code, arch_initcall(hugetlbpage_init) happens after N_MEMORY mask is setup. I can't imagine any arch code setting up huge pages before N_MEMORY. But, I suppose it is possible and we would need to somehow guarantee this. > 2. CMA reservation is available to be called at arch_initcall() Since I am pretty sure we can delay the reservation until hugetlb command line processing time, it would be great if it was always done there. Unfortunately, I can not immediately think of an easy way to do this. -- Mike Kravetz
