Re: [PATCH 4/6] hugetlb: avoid allocation failed when page reporting is on going

[Alexander Duyck]

On Tue, Jan 5, 2021 at 7:50 PM Liang Li <liliang324@xxxxxxxxx> wrote:
>
> Page reporting isolates free pages temporarily when reporting
> free pages information. It will reduce the actual free pages
> and may cause application failed for no enough available memory.
> This patch try to solve this issue, when there is no free page
> and page repoting is on going, wait until it is done.
>
> Cc: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>

Please don't use this email address for me anymore. Either use
alexander.duyck@xxxxxxxxx or alexanderduyck@xxxxxx. I am getting
bounces when I reply to this thread because of the old address.

> Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
> Cc: David Hildenbrand <david@xxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Alex Williamson <alex.williamson@xxxxxxxxxx>
> Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
> Cc: Liang Li <liliang324@xxxxxxxxx>
> Signed-off-by: Liang Li <liliangleo@xxxxxxxxxxxxxx>
> ---
>  include/linux/hugetlb.h | 2 ++
>  mm/hugetlb.c            | 9 +++++++++
>  mm/page_reporting.c     | 6 +++++-
>  3 files changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index d55e6a00b3dc..73b2934ba91c 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -490,6 +490,7 @@ struct hstate {
>         unsigned long resv_huge_pages;
>         unsigned long surplus_huge_pages;
>         unsigned long nr_overcommit_huge_pages;
> +       unsigned long isolated_huge_pages;
>         struct list_head hugepage_activelist;
>         struct list_head hugepage_freelists[MAX_NUMNODES];
>         unsigned int nr_huge_pages_node[MAX_NUMNODES];
> @@ -500,6 +501,7 @@ struct hstate {
>         struct cftype cgroup_files_dfl[7];
>         struct cftype cgroup_files_legacy[9];
>  #endif
> +       struct mutex mtx_prezero;
>         char name[HSTATE_NAME_LEN];
>  };
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index eb533995cb49..0fccd5f96954 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -2320,6 +2320,12 @@ struct page *alloc_huge_page(struct vm_area_struct *vma,
>                 goto out_uncharge_cgroup_reservation;
>
>         spin_lock(&hugetlb_lock);
> +       while (h->free_huge_pages <= 1 && h->isolated_huge_pages) {
> +               spin_unlock(&hugetlb_lock);
> +               mutex_lock(&h->mtx_prezero);
> +               mutex_unlock(&h->mtx_prezero);
> +               spin_lock(&hugetlb_lock);
> +       }

This seems like a bad idea. It kind of defeats the whole point of
doing the page zeroing outside of the hugetlb_lock. Also it is
operating on the assumption that the only way you might get a page is
from the page zeroing logic.

With the page reporting code we wouldn't drop the count to zero. We
had checks that were going through and monitoring the watermarks and
if we started to hit the low watermark we would stop page reporting
and just assume there aren't enough pages to report. You might need to
look at doing something similar here so that you can avoid colliding
with the allocator.


>         /*
>          * glb_chg is passed to indicate whether or not a page must be taken
>          * from the global free pool (global change).  gbl_chg == 0 indicates
> @@ -3208,6 +3214,7 @@ void __init hugetlb_add_hstate(unsigned int order)
>         INIT_LIST_HEAD(&h->hugepage_activelist);
>         h->next_nid_to_alloc = first_memory_node;
>         h->next_nid_to_free = first_memory_node;
> +       mutex_init(&h->mtx_prezero);
>         snprintf(h->name, HSTATE_NAME_LEN, "hugepages-%lukB",
>                                         huge_page_size(h)/1024);
>
> @@ -5541,6 +5548,7 @@ void isolate_free_huge_page(struct page *page, struct hstate *h, int nid)
>
>         list_move(&page->lru, &h->hugepage_activelist);
>         set_page_refcounted(page);
> +       h->isolated_huge_pages++;
>  }
>
>  void putback_isolate_huge_page(struct hstate *h, struct page *page)
> @@ -5548,6 +5556,7 @@ void putback_isolate_huge_page(struct hstate *h, struct page *page)
>         int nid = page_to_nid(page);
>
>         list_move(&page->lru, &h->hugepage_freelists[nid]);
> +       h->isolated_huge_pages--;
>  }
>
>  bool isolate_huge_page(struct page *page, struct list_head *list)
> diff --git a/mm/page_reporting.c b/mm/page_reporting.c
> index cc31696225bb..99e1e688d7c1 100644
> --- a/mm/page_reporting.c
> +++ b/mm/page_reporting.c
> @@ -272,12 +272,15 @@ hugepage_reporting_process_hstate(struct page_reporting_dev_info *prdev,
>         int ret = 0, nid;
>
>         offset = max_items;
> +       mutex_lock(&h->mtx_prezero);
>         for (nid = 0; nid < MAX_NUMNODES; nid++) {
>                 ret = hugepage_reporting_cycle(prdev, h, nid, sgl, &offset,
>                                                max_items);
>
> -               if (ret < 0)
> +               if (ret < 0) {
> +                       mutex_unlock(&h->mtx_prezero);
>                         return ret;
> +               }
>         }
>
>         /* report the leftover pages before going idle */
> @@ -291,6 +294,7 @@ hugepage_reporting_process_hstate(struct page_reporting_dev_info *prdev,
>                 hugepage_reporting_drain(prdev, h, sgl, leftover, !ret);
>                 spin_unlock(&hugetlb_lock);
>         }
> +       mutex_unlock(&h->mtx_prezero);
>
>         return ret;
>  }
> --
> 2.18.2
>
>