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

Henry Burns
2019-07-15T19:57:16Z

>>
>> 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 <henryburns@google.com>
>> ---
>> mm/z3fold.c | 10 ++++++++++
>> 1 file changed, 10 insertions(+)
>>
>> diff --git a/mm/z3fold.c b/mm/z3fold.c
>> index 42ef9955117c..9da471bcab93 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 this list is empty, so we only
>> + * have to reinitialize it.
>> + */
>
>
> On the nitpicking side, we seem to have ensured that directly in migrate :) Looks OK to me otherwise.
Ok, I see it happens in the call to do_compact_page(). Got it, new
patch coming out now.

>
> ~Vitaly
>
>> + INIT_LIST_HEAD(&new_zhdr->buddy);
>> new_mapping = page_mapping(page);
>> __ClearPageMovable(page);
>> ClearPagePrivate(page);
>> --
>> 2.22.0.510.g264f2c817a-goog
>>