On Mon, Sep 21, 2020 at 10:42:56AM -0700, Minchan Kim wrote:
> IIRC, the problem was runtime pte popluating needs GFP_KERNEL but
> zs_map_object API runs under non-preemtible section.
Make sense.
> > - area->vm = alloc_vm_area(PAGE_SIZE * 2, NULL);
> > + area->vm = get_vm_area(PAGE_SIZE * 2, 0);
> > if (!area->vm)
> > return -ENOMEM;
> > return 0;
>
> I think it shoud work.
>
> diff --git a/mm/memory.c b/mm/memory.c
> index 05789aa4af12..6a1e4d854593 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2232,7 +2232,7 @@ static int apply_to_pte_range(struct mm_struct *mm, pmd_t *pmd,
> arch_enter_lazy_mmu_mode();
>
> do {
> - if (create || !pte_none(*pte)) {
> + if ((create || !pte_none(*pte)) && fn) {
> err = fn(pte++, addr, data);
> if (err)
> break;
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index 3e4fe3259612..9ef7daf3d279 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -1116,6 +1116,8 @@ static struct zspage *find_get_zspage(struct size_class *class)
> #ifdef CONFIG_ZSMALLOC_PGTABLE_MAPPING
> static inline int __zs_cpu_up(struct mapping_area *area)
> {
> + int ret;
> +
> /*
> * Make sure we don't leak memory if a cpu UP notification
> * and zs_init() race and both call zs_cpu_up() on the same cpu
> @@ -1125,7 +1127,13 @@ static inline int __zs_cpu_up(struct mapping_area *area)
> area->vm = get_vm_area(PAGE_SIZE * 2, 0);
> if (!area->vm)
> return -ENOMEM;
> - return 0;
> +
> + /*
> + * Populate ptes in advance to avoid pte allocation with GFP_KERNEL
> + * in non-preemtible context of zs_map_object.
> + */
> + ret = apply_to_page_range(&init_mm, NULL, PAGE_SIZE * 2, NULL, NULL);
> + return ret;
I think this needs the addr from the vm area somewhere..
We probaby want to add a trivial helper to prefault an area instead of
the open coded variant.
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