On Fri, Sep 18, 2020 at 06:37:19PM +0200, Christoph Hellwig wrote:
> There is no obvious reason why zsmalloc needs to pre-fault the PTEs
> given that it later uses map_kernel_range to just like vmap().
IIRC, the problem was runtime pte popluating needs GFP_KERNEL but
zs_map_object API runs under non-preemtible section.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
> mm/zsmalloc.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index c36fdff9a37131..3e4fe3259612fd 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -1122,7 +1122,7 @@ static inline int __zs_cpu_up(struct mapping_area *area)
> */
> if (area->vm)
> return 0;
> - 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;
}
static inline void __zs_cpu_down(struct mapping_area *area)
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