Re: [External] RE: [PATCH v6 14/16] mm/hugetlb: Add a kernel parameter hugetlb_free_vmemmap

[Muchun Song <songmuchun@bytedance.com>]

On Tue, Nov 24, 2020 at 6:54 PM Song Bao Hua (Barry Song)
<song.bao.hua@hisilicon.com> wrote:
>
>
>
> > -----Original Message-----
> > From: Muchun Song [mailto:songmuchun@bytedance.com]
> > Sent: Tuesday, November 24, 2020 10:53 PM
> > To: corbet@lwn.net; mike.kravetz@oracle.com; tglx@linutronix.de;
> > mingo@redhat.com; bp@alien8.de; x86@kernel.org; hpa@zytor.com;
> > dave.hansen@linux.intel.com; luto@kernel.org; peterz@infradead.org;
> > viro@zeniv.linux.org.uk; akpm@linux-foundation.org; paulmck@kernel.org;
> > mchehab+huawei@kernel.org; pawan.kumar.gupta@linux.intel.com;
> > rdunlap@infradead.org; oneukum@suse.com; anshuman.khandual@arm.com;
> > jroedel@suse.de; almasrymina@google.com; rientjes@google.com;
> > willy@infradead.org; osalvador@suse.de; mhocko@suse.com; Song Bao Hua
> > (Barry Song) <song.bao.hua@hisilicon.com>
> > Cc: duanxiongchun@bytedance.com; linux-doc@vger.kernel.org;
> > linux-kernel@vger.kernel.org; linux-mm@kvack.org;
> > linux-fsdevel@vger.kernel.org; Muchun Song <songmuchun@bytedance.com>
> > Subject: [PATCH v6 14/16] mm/hugetlb: Add a kernel parameter
> > hugetlb_free_vmemmap
> >
> > Add a kernel parameter hugetlb_free_vmemmap to disable the feature of
> > freeing unused vmemmap pages associated with each hugetlb page on boot.
> >
> > Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> > ---
> >  Documentation/admin-guide/kernel-parameters.txt |  9 +++++++++
> >  Documentation/admin-guide/mm/hugetlbpage.rst    |  3 +++
> >  mm/hugetlb_vmemmap.c                            | 19
> > ++++++++++++++++++-
> >  3 files changed, 30 insertions(+), 1 deletion(-)
> >
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt
> > b/Documentation/admin-guide/kernel-parameters.txt
> > index 5debfe238027..d28c3acde965 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -1551,6 +1551,15 @@
> >                       Documentation/admin-guide/mm/hugetlbpage.rst.
> >                       Format: size[KMG]
> >
> > +     hugetlb_free_vmemmap=
> > +                     [KNL] When CONFIG_HUGETLB_PAGE_FREE_VMEMMAP is set,
> > +                     this controls freeing unused vmemmap pages associated
> > +                     with each HugeTLB page.
> > +                     Format: { on | off (default) }
> > +
> > +                     on:  enable the feature
> > +                     off: disable the feature
> > +
>
> We've a parameter here. but wouldn't it be applied to "x86/mm/64/:disable
> Pmd page mapping of vmemmap" as well?
> If (hugetlb_free_vmemmap_enabled)
>         Do Basepage mapping?

Oh, yeah, we can. Thanks.

>
> >       hung_task_panic=
> >                       [KNL] Should the hung task detector generate panics.
> >                       Format: 0 | 1
> > diff --git a/Documentation/admin-guide/mm/hugetlbpage.rst
> > b/Documentation/admin-guide/mm/hugetlbpage.rst
> > index f7b1c7462991..6a8b57f6d3b7 100644
> > --- a/Documentation/admin-guide/mm/hugetlbpage.rst
> > +++ b/Documentation/admin-guide/mm/hugetlbpage.rst
> > @@ -145,6 +145,9 @@ default_hugepagesz
> >
> >       will all result in 256 2M huge pages being allocated.  Valid default
> >       huge page size is architecture dependent.
> > +hugetlb_free_vmemmap
> > +     When CONFIG_HUGETLB_PAGE_FREE_VMEMMAP is set, this enables
> > freeing
> > +     unused vmemmap pages associated each HugeTLB page.
> >
> >  When multiple huge page sizes are supported, ``/proc/sys/vm/nr_hugepages``
> >  indicates the current number of pre-allocated huge pages of the default size.
> > diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
> > index 509ca451e232..b2222f8d1245 100644
> > --- a/mm/hugetlb_vmemmap.c
> > +++ b/mm/hugetlb_vmemmap.c
> > @@ -131,6 +131,22 @@ typedef void (*vmemmap_pte_remap_func_t)(struct
> > page *reuse, pte_t *ptep,
> >                                        unsigned long start, unsigned long end,
> >                                        void *priv);
> >
> > +static bool hugetlb_free_vmemmap_enabled __initdata;
> > +
> > +static int __init early_hugetlb_free_vmemmap_param(char *buf)
> > +{
> > +     if (!buf)
> > +             return -EINVAL;
> > +
> > +     if (!strcmp(buf, "on"))
> > +             hugetlb_free_vmemmap_enabled = true;
> > +     else if (strcmp(buf, "off"))
> > +             return -EINVAL;
> > +
> > +     return 0;
> > +}
> > +early_param("hugetlb_free_vmemmap",
> > early_hugetlb_free_vmemmap_param);
> > +
> >  static inline unsigned int vmemmap_pages_per_hpage(struct hstate *h)
> >  {
> >       return free_vmemmap_pages_per_hpage(h) + RESERVE_VMEMMAP_NR;
> > @@ -322,7 +338,8 @@ void __init hugetlb_vmemmap_init(struct hstate *h)
> >       unsigned int order = huge_page_order(h);
> >       unsigned int vmemmap_pages;
> >
> > -     if (!is_power_of_2(sizeof(struct page))) {
> > +     if (!is_power_of_2(sizeof(struct page)) ||
> > +         !hugetlb_free_vmemmap_enabled) {
> >               pr_info("disable freeing vmemmap pages for %s\n", h->name);
> >               return;
> >       }
> > --
> > 2.11.0
>
> Thanks
> Barry
>


-- 
Yours,
Muchun