On 2022/7/4 9:33, Naoya Horiguchi wrote:
> From: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
>
> I found a weird state of 1GB hugepage pool, caused by the following
> procedure:
>
> - run a process reserving all free 1GB hugepages,
> - shrink free 1GB hugepage pool to zero (i.e. writing 0 to
> /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages), then
> - kill the reserving process.
>
> , then all the hugepages are free *and* surplus at the same time.
>
> $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages
> 3
> $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/free_hugepages
> 3
> $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/resv_hugepages
> 0
> $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/surplus_hugepages
> 3
>
> This state is resolved by reserving and allocating the pages then
> freeing them again, so this seems not to result in serious problem.
> But it's a little surprising (shrinking pool suddenly fails).
>
> This behavior is caused by hstate_is_gigantic() check in
> return_unused_surplus_pages(). This was introduced so long ago in 2008
> by commit aa888a74977a ("hugetlb: support larger than MAX_ORDER"), and
> at that time the gigantic pages were not supposed to be allocated/freed
> at run-time. Now kernel can support runtime allocation/free, so let's
> check gigantic_page_runtime_supported() together.
>
> Signed-off-by: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
This patch looks good to me with a few question below.
> ---
> v2 -> v3:
> - Fixed typo in patch description,
> - add !gigantic_page_runtime_supported() check instead of removing
> hstate_is_gigantic() check (suggested by Miaohe and Muchun)
> - add a few more !gigantic_page_runtime_supported() check in
> set_max_huge_pages() (by Mike).
> ---
> mm/hugetlb.c | 19 ++++++++++++++++---
> 1 file changed, 16 insertions(+), 3 deletions(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 2a554f006255..bdc4499f324b 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -2432,8 +2432,7 @@ static void return_unused_surplus_pages(struct hstate *h,
> /* Uncommit the reservation */
> h->resv_huge_pages -= unused_resv_pages;
>
> - /* Cannot return gigantic pages currently */
> - if (hstate_is_gigantic(h))
> + if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported())
> goto out;
>
> /*
> @@ -3315,7 +3314,8 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
> * the user tries to allocate gigantic pages but let the user free the
> * boottime allocated gigantic pages.
> */
> - if (hstate_is_gigantic(h) && !IS_ENABLED(CONFIG_CONTIG_ALLOC)) {
> + if (hstate_is_gigantic(h) && (!IS_ENABLED(CONFIG_CONTIG_ALLOC) ||
> + !gigantic_page_runtime_supported())) {
> if (count > persistent_huge_pages(h)) {
> spin_unlock_irq(&hugetlb_lock);
> mutex_unlock(&h->resize_lock);
> @@ -3363,6 +3363,19 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
> goto out;
> }
>
> + /*
> + * We can not decrease gigantic pool size if runtime modification
> + * is not supported.
> + */
> + if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported()) {
> + if (count < persistent_huge_pages(h)) {
> + spin_unlock_irq(&hugetlb_lock);
> + mutex_unlock(&h->resize_lock);
> + NODEMASK_FREE(node_alloc_noretry);
> + return -EINVAL;
> + }
> + }
With above change, we're not allowed to decrease the pool size now. But it was allowed previously
even if !gigantic_page_runtime_supported. Does this will break user?
And it seems it's not allowed to adjust the max_huge_pages now if !gigantic_page_runtime_supported
for gigantic huge page. Should we just return for such case as there should be nothing to do now?
Or am I miss something?
Thanks!
> +
> /*
> * Decrease the pool size
> * First return free pages to the buddy allocator (being careful
>
