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Wed, 09 Dec 2020 07:51:35 -0800 (PST) MIME-Version: 1.0 References: <20201130151838.11208-1-songmuchun@bytedance.com> <20201130151838.11208-7-songmuchun@bytedance.com> <4b8a9389-1704-4d8c-ec58-abd753814dd9@redhat.com> <33779de1-7a7a-aa5c-e756-92925d4b097d@redhat.com> In-Reply-To: <33779de1-7a7a-aa5c-e756-92925d4b097d@redhat.com> From: Muchun Song Date: Wed, 9 Dec 2020 23:50:58 +0800 Message-ID: Subject: Re: [External] Re: [PATCH v7 06/15] mm/hugetlb: Disable freeing vmemmap if struct page size is not power of two To: David Hildenbrand Cc: Jonathan Corbet , Mike Kravetz , Thomas Gleixner , mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, dave.hansen@linux.intel.com, luto@kernel.org, Peter Zijlstra , viro@zeniv.linux.org.uk, Andrew Morton , paulmck@kernel.org, mchehab+huawei@kernel.org, pawan.kumar.gupta@linux.intel.com, Randy Dunlap , oneukum@suse.com, anshuman.khandual@arm.com, jroedel@suse.de, Mina Almasry , David Rientjes , Matthew Wilcox , Oscar Salvador , Michal Hocko , "Song Bao Hua (Barry Song)" , Xiongchun duan , linux-doc@vger.kernel.org, LKML , Linux Memory Management List , linux-fsdevel Content-Type: text/plain; charset="UTF-8" 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 Wed, Dec 9, 2020 at 11:48 PM David Hildenbrand wrote: > > On 09.12.20 16:13, Muchun Song wrote: > > On Wed, Dec 9, 2020 at 6:10 PM David Hildenbrand wrote: > >> > >> On 09.12.20 11:06, David Hildenbrand wrote: > >>> On 09.12.20 11:03, Muchun Song wrote: > >>>> On Wed, Dec 9, 2020 at 5:57 PM David Hildenbrand wrote: > >>>>> > >>>>> On 30.11.20 16:18, Muchun Song wrote: > >>>>>> We only can free the tail vmemmap pages of HugeTLB to the buddy allocator > >>>>>> when the size of struct page is a power of two. > >>>>>> > >>>>>> Signed-off-by: Muchun Song > >>>>>> --- > >>>>>> mm/hugetlb_vmemmap.c | 5 +++++ > >>>>>> 1 file changed, 5 insertions(+) > >>>>>> > >>>>>> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c > >>>>>> index 51152e258f39..ad8fc61ea273 100644 > >>>>>> --- a/mm/hugetlb_vmemmap.c > >>>>>> +++ b/mm/hugetlb_vmemmap.c > >>>>>> @@ -111,6 +111,11 @@ void __init hugetlb_vmemmap_init(struct hstate *h) > >>>>>> unsigned int nr_pages = pages_per_huge_page(h); > >>>>>> unsigned int vmemmap_pages; > >>>>>> > >>>>>> + if (!is_power_of_2(sizeof(struct page))) { > >>>>>> + pr_info("disable freeing vmemmap pages for %s\n", h->name); > >>>>> > >>>>> I'd just drop that pr_info(). Users are able to observe that it's > >>>>> working (below), so they are able to identify that it's not working as well. > >>>> > >>>> The below is just a pr_debug. Do you suggest converting it to pr_info? > >>> > >>> Good question. I wonder if users really have to know in most cases. > >>> Maybe pr_debug() is good enough in environments where we want to debug > >>> why stuff is not working as expected. > >>> > >> > >> Oh, another thought, can we glue availability of > >> HUGETLB_PAGE_FREE_VMEMMAP (or a new define based on the config and the > >> size of a stuct page) to the size of struct page somehow? > >> > >> I mean, it's known at compile time that this will never work. > > > > I want to define a macro which indicates the size of the > > struct page. There is place (kernel/bounds.c) where can > > do similar things. When I added the following code in > > that file. > > > > DEFINE(STRUCT_PAGE_SIZE, sizeof(struct page)); > > > > Then the compiler will output a message like: > > > > Hm, from what I understand you cannot use sizeof() in #if etc. So it > might not be possible after all. At least the compiler should optimize > code like > > if (!is_power_of_2(sizeof(struct page))) { > // either this > } else { > // or that > } > > that can never be reached Got it. Thanks so much. > > -- > Thanks, > > David / dhildenb > -- Yours, Muchun