linux-kernel - Re: [External] Re: [PATCH v7 06/15] mm/hugetlb: Disable freeing vmemmap if struct page size is not power of two

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Date:   Wed, 9 Dec 2020 18:10:50 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Jonathan Corbet <corbet@....net>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Thomas Gleixner <tglx@...utronix.de>, mingo@...hat.com,
        bp@...en8.de, x86@...nel.org, hpa@...or.com,
        dave.hansen@...ux.intel.com, luto@...nel.org,
        Peter Zijlstra <peterz@...radead.org>, viro@...iv.linux.org.uk,
        Andrew Morton <akpm@...ux-foundation.org>, paulmck@...nel.org,
        mchehab+huawei@...nel.org, pawan.kumar.gupta@...ux.intel.com,
        Randy Dunlap <rdunlap@...radead.org>, oneukum@...e.com,
        anshuman.khandual@....com, jroedel@...e.de,
        Mina Almasry <almasrymina@...gle.com>,
        David Rientjes <rientjes@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Oscar Salvador <osalvador@...e.de>,
        Michal Hocko <mhocko@...e.com>,
        "Song Bao Hua (Barry Song)" <song.bao.hua@...ilicon.com>,
        Xiongchun duan <duanxiongchun@...edance.com>,
        linux-doc@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [External] Re: [PATCH v7 06/15] mm/hugetlb: Disable freeing
 vmemmap if struct page size is not power of two

On Wed, Dec 9, 2020 at 6:06 PM David Hildenbrand <david@...hat.com> wrote:
>
> On 09.12.20 11:03, Muchun Song wrote:
> > On Wed, Dec 9, 2020 at 5:57 PM David Hildenbrand <david@...hat.com> 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 <songmuchun@...edance.com>
> >>> ---
> >>>  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.

When someone enables this feature via the boot cmdline, maybe he should
want to know whether this feature works. From this point of view, the pr_info
is necessary. Right?

>
> --
> Thanks,
>
> David / dhildenb
>


-- 
Yours,
Muchun