Nishanth Aravamudan <nacc@xxxxxxxxxxxxxxxxxx> writes:
> In KVM guests on Power, in a guest not backed by hugepages, we see the
> following:
>
> AnonHugePages: 0 kB
> HugePages_Total: 0
> HugePages_Free: 0
> HugePages_Rsvd: 0
> HugePages_Surp: 0
> Hugepagesize: 64 kB
>
> HPAGE_SHIFT == 0 in this configuration, which indicates that hugepages
> are not supported at boot-time, but this is only checked in
> hugetlb_init(). Extract the check to a helper function, and use it in a
> few relevant places.
>
> This does make hugetlbfs not supported (not registered at all) in this
> environment. I believe this is fine, as there are no valid hugepages and
> that won't change at runtime.
>
> Signed-off-by: Nishanth Aravamudan <nacc@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
>
> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
> index d19b30a..cc8fcc7 100644
> --- a/fs/hugetlbfs/inode.c
> +++ b/fs/hugetlbfs/inode.c
> @@ -1017,6 +1017,11 @@ static int __init init_hugetlbfs_fs(void)
> int error;
> int i;
>
> + if (!hugepages_supported()) {
> + printk(KERN_ERR "hugetlbfs: Disabling because there are no supported hugepage sizes\n");
> + return -ENOTSUPP;
> + }
> +
> error = bdi_init(&hugetlbfs_backing_dev_info);
> if (error)
> return error;
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index 8c43cc4..0aea8de 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -450,4 +450,14 @@ static inline spinlock_t *huge_pte_lock(struct hstate *h,
> return ptl;
> }
>
> +static inline bool hugepages_supported(void)
> +{
> + /*
> + * Some platform decide whether they support huge pages at boot
> + * time. On these, such as powerpc, HPAGE_SHIFT is set to 0 when
> + * there is no such support
> + */
> + return HPAGE_SHIFT != 0;
> +}
> +
> #endif /* _LINUX_HUGETLB_H */
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index c01cb9f..1c99585 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1949,11 +1949,7 @@ module_exit(hugetlb_exit);
>
> static int __init hugetlb_init(void)
> {
> - /* Some platform decide whether they support huge pages at boot
> - * time. On these, such as powerpc, HPAGE_SHIFT is set to 0 when
> - * there is no such support
> - */
> - if (HPAGE_SHIFT == 0)
> + if (!hugepages_supported())
> return 0;
>
> if (!size_to_hstate(default_hstate_size)) {
> @@ -2069,6 +2065,9 @@ static int hugetlb_sysctl_handler_common(bool obey_mempolicy,
> unsigned long tmp;
> int ret;
>
> + if (!hugepages_supported())
> + return -ENOTSUPP;
> +
> tmp = h->max_huge_pages;
>
> if (write && h->order >= MAX_ORDER)
> @@ -2122,6 +2121,9 @@ int hugetlb_overcommit_handler(struct ctl_table *table, int write,
> unsigned long tmp;
> int ret;
>
> + if (!hugepages_supported())
> + return -ENOTSUPP;
> +
> tmp = h->nr_overcommit_huge_pages;
>
> if (write && h->order >= MAX_ORDER)
> @@ -2147,6 +2149,8 @@ out:
> void hugetlb_report_meminfo(struct seq_file *m)
> {
> struct hstate *h = &default_hstate;
> + if (!hugepages_supported())
> + return;
> seq_printf(m,
> "HugePages_Total: %5lu\n"
> "HugePages_Free: %5lu\n"
> @@ -2163,6 +2167,8 @@ void hugetlb_report_meminfo(struct seq_file *m)
> int hugetlb_report_node_meminfo(int nid, char *buf)
> {
> struct hstate *h = &default_hstate;
> + if (!hugepages_supported())
> + return 0;
> return sprintf(buf,
> "Node %d HugePages_Total: %5u\n"
> "Node %d HugePages_Free: %5u\n"
> @@ -2177,6 +2183,9 @@ void hugetlb_show_meminfo(void)
> struct hstate *h;
> int nid;
>
> + if (!hugepages_supported())
> + return;
> +
> for_each_node_state(nid, N_MEMORY)
> for_each_hstate(h)
> pr_info("Node %d hugepages_total=%u hugepages_free=%u hugepages_surp=%u hugepages_size=%lukB\n",
--
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