2019-07-16 00:08:40

by Henry Burns

Subject: [PATCH v2] mm/z3fold.c: Reinitialize zhdr structs after migration

z3fold_page_migration() calls memcpy(new_zhdr, zhdr, PAGE_SIZE).
However, zhdr contains fields that can't be directly coppied over (ex:
list_head, a circular linked list). We only need to initialize the
linked lists in new_zhdr, as z3fold_isolate_page() already ensures
that these lists are empty

Additionally it is possible that zhdr->work has been placed in a
workqueue. In this case we shouldn't migrate the page, as zhdr->work
references zhdr as opposed to new_zhdr.

Fixes: bba4c5f96ce4 ("mm/z3fold.c: support page migration")
Signed-off-by: Henry Burns <[email protected]>
---
Changelog since v1:
- Made comments explicityly refer to new_zhdr->buddy.

mm/z3fold.c | 10 ++++++++++
1 file changed, 10 insertions(+)

diff --git a/mm/z3fold.c b/mm/z3fold.c
index 42ef9955117c..f4b2283b19a3 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -1352,12 +1352,22 @@ static int z3fold_page_migrate(struct address_space *mapping, struct page *newpa
z3fold_page_unlock(zhdr);
return -EBUSY;
}
+ if (work_pending(&zhdr->work)) {
+ z3fold_page_unlock(zhdr);
+ return -EAGAIN;
+ }
new_zhdr = page_address(newpage);
memcpy(new_zhdr, zhdr, PAGE_SIZE);
newpage->private = page->private;
page->private = 0;
z3fold_page_unlock(zhdr);
spin_lock_init(&new_zhdr->page_lock);
+ INIT_WORK(&new_zhdr->work, compact_page_work);
+ /*
+ * z3fold_page_isolate() ensures that new_zhdr->buddy is empty,
+ * so we only have to reinitialize it.
+ */
+ INIT_LIST_HEAD(&new_zhdr->buddy);
new_mapping = page_mapping(page);
__ClearPageMovable(page);
ClearPagePrivate(page);
--
2.22.0.510.g264f2c817a-goog

2019-07-16 21:22:04

by Shakeel Butt

Subject: Re: [PATCH v2] mm/z3fold.c: Reinitialize zhdr structs after migration

On Mon, Jul 15, 2019 at 5:05 PM Henry Burns <[email protected]> wrote:
>
> z3fold_page_migration() calls memcpy(new_zhdr, zhdr, PAGE_SIZE).
> However, zhdr contains fields that can't be directly coppied over (ex:
> list_head, a circular linked list). We only need to initialize the
> linked lists in new_zhdr, as z3fold_isolate_page() already ensures
> that these lists are empty
>
> Additionally it is possible that zhdr->work has been placed in a
> workqueue. In this case we shouldn't migrate the page, as zhdr->work
> references zhdr as opposed to new_zhdr.
>
> Fixes: bba4c5f96ce4 ("mm/z3fold.c: support page migration")
> Signed-off-by: Henry Burns <[email protected]>

Reviewed-by: Shakeel Butt <[email protected]>

> ---
> Changelog since v1:
> - Made comments explicityly refer to new_zhdr->buddy.
>
> mm/z3fold.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/mm/z3fold.c b/mm/z3fold.c
> index 42ef9955117c..f4b2283b19a3 100644
> --- a/mm/z3fold.c
> +++ b/mm/z3fold.c
> @@ -1352,12 +1352,22 @@ static int z3fold_page_migrate(struct address_space *mapping, struct page *newpa
> z3fold_page_unlock(zhdr);
> return -EBUSY;
> }
> + if (work_pending(&zhdr->work)) {
> + z3fold_page_unlock(zhdr);
> + return -EAGAIN;
> + }
> new_zhdr = page_address(newpage);
> memcpy(new_zhdr, zhdr, PAGE_SIZE);
> newpage->private = page->private;
> page->private = 0;
> z3fold_page_unlock(zhdr);
> spin_lock_init(&new_zhdr->page_lock);
> + INIT_WORK(&new_zhdr->work, compact_page_work);
> + /*
> + * z3fold_page_isolate() ensures that new_zhdr->buddy is empty,
> + * so we only have to reinitialize it.
> + */
> + INIT_LIST_HEAD(&new_zhdr->buddy);
> new_mapping = page_mapping(page);
> __ClearPageMovable(page);
> ClearPagePrivate(page);
> --
> 2.22.0.510.g264f2c817a-goog
>