On Fri 20-11-20 14:43:21, Muchun Song wrote:
> Add a kernel parameter hugetlb_free_vmemmap to disable the feature of
> freeing unused vmemmap pages associated with each hugetlb page on boot.
As replied to the config patch. This is fine but I would argue that the
default should be flipped. Saving memory is nice but it comes with
overhead and therefore should be an opt-in. The config option should
only guard compile time dependencies not a user choice.
> Signed-off-by: Muchun Song <songmuc...@bytedance.com>
> ---
> Documentation/admin-guide/kernel-parameters.txt | 9 +++++++++
> Documentation/admin-guide/mm/hugetlbpage.rst | 3 +++
> mm/hugetlb_vmemmap.c | 21 +++++++++++++++++++++
> 3 files changed, 33 insertions(+)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt
> b/Documentation/admin-guide/kernel-parameters.txt
> index 5debfe238027..ccf07293cb63 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 (default) | off }
> +
> + on: enable the feature
> + off: disable the feature
> +
> 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..7d6129ee97dd 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 disables 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 3629165d8158..c958699d1393 100644
> --- a/mm/hugetlb_vmemmap.c
> +++ b/mm/hugetlb_vmemmap.c
> @@ -144,6 +144,22 @@ static inline bool vmemmap_pmd_huge(pmd_t *pmd)
> }
> #endif
>
> +static bool hugetlb_free_vmemmap_disabled __initdata;
> +
> +static int __init early_hugetlb_free_vmemmap_param(char *buf)
> +{
> + if (!buf)
> + return -EINVAL;
> +
> + if (!strcmp(buf, "off"))
> + hugetlb_free_vmemmap_disabled = true;
> + else if (strcmp(buf, "on"))
> + 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;
> @@ -541,6 +557,11 @@ void __init hugetlb_vmemmap_init(struct hstate *h)
> unsigned int order = huge_page_order(h);
> unsigned int vmemmap_pages;
>
> + if (hugetlb_free_vmemmap_disabled) {
> + pr_info("disable free vmemmap pages for %s\n", h->name);
> + return;
> + }
> +
> vmemmap_pages = ((1 << order) * sizeof(struct page)) >> PAGE_SHIFT;
> /*
> * The head page and the first tail page are not to be freed to buddy
> --
> 2.11.0
--
Michal Hocko
SUSE Labs
