Re: [PATCH v3] mm/page_alloc: clear page->private in free_pages_prepare()

[Zi Yan <ziy@nvidia.com>]

On 9 Feb 2026, at 20:20, Baolin Wang wrote:

> On 2/10/26 3:42 AM, Zi Yan wrote:
>> On 9 Feb 2026, at 14:39, David Hildenbrand (Arm) wrote:
>>
>>> On 2/9/26 18:44, Zi Yan wrote:
>>>> On 9 Feb 2026, at 12:36, David Hildenbrand (Arm) wrote:
>>>>
>>>>> On 2/9/26 17:33, Zi Yan wrote:
>>>>>>
>>>>>>
>>>>>> I agree. Silently fixing non zero ->private just moves the work/responsibility
>>>>>> from users to core mm. They could do better. :)
>>>>>>
>>>>>> We can have a patch or multiple patches to fix users do not zero ->private
>>>>>> when freeing a page and add the patch below.
>>>>>
>>>>> Do we know roughly which ones don't zero it out?
>>>>
>>>> So far based on [1], I found:
>>>>
>>>> 1. shmem_swapin_folio() in mm/shmem.c does not zero ->swap.val (overlapping
>>>> with private);
>
> After Kairui’s series [1], the shmem part looks good to me. As we no longer skip the swapcache now, we shouldn’t clear the ->swap.val of a swapcache folio if failed to swap-in.

What do you mean by "after Kairui's series[1]"? Can you elaborate a little bit more?

For the diff below, does the "folio_put(folio)" have different outcomes based on
skip_swapcache? Only if skip_swapcache is true, "folio_put(folio)" frees the folio?

Thanks.

diff --git a/mm/shmem.c b/mm/shmem.c
index ec6c01378e9d..546e193ef993 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2437,8 +2437,10 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index,
 failed_nolock:
        if (skip_swapcache)
                swapcache_clear(si, folio->swap, folio_nr_pages(folio));
-       if (folio)
+       if (folio) {
+               folio->swap.val = 0;
                folio_put(folio);
+       }
        put_swap_device(si);

        return error;

>
> [1]https://lore.kernel.org/all/20251219195751.61328-1-ryncsn@gmail.com/T/#mcba8a32e1021dc28ce1e824c9d042dca316a30d7
>
>>>> 2. __free_slab() in mm/slub.c does not zero ->inuse, ->objects, ->frozen
>>>> (overlapping with private).
>>>>
>>>> Mikhail found ttm_pool_unmap_and_free() in drivers/gpu/drm/ttm/ttm_pool.c
>>>> does not zero ->private, which stores page order.


--
Best Regards,
Yan, Zi