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@lst.de

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)