Re: [PATCH STABLE v6.1.y] mm/migrate: set swap entry values of THP tail pages properly.

Charan Teja Kalla
2024-03-13T11:23:39Z

On 3/6/2024 9:22 PM, Zi Yan wrote:
> From: Zi Yan <ziy@nvidia.com>
>
> The tail pages in a THP can have swap entry information stored in their
> private field. When migrating to a new page, all tail pages of the new
> page need to update ->private to avoid future data corruption.
>
> This fix is stable-only, since after commit 07e09c483cbe ("mm/huge_memory:
> work on folio->swap instead of page->private when splitting folio"),
> subpages of a swapcached THP no longer requires the maintenance.
>
> Adding THPs to the swapcache was introduced in commit
> 38d8b4e6bdc87 ("mm, THP, swap: delay splitting THP during swap out"),
> where each subpage of a THP added to the swapcache had its own swapcache
> entry and required the ->private field to point to the correct swapcache
> entry. Later, when THP migration functionality was implemented in commit
> 616b8371539a6 ("mm: thp: enable thp migration in generic path"),
> it initially did not handle the subpages of swapcached THPs, failing to
> update their ->private fields or replace the subpage pointers in the
> swapcache. Subsequently, commit e71769ae5260 ("mm: enable thp migration
> for shmem thp") addressed the swapcache update aspect. This patch fixes
> the update of subpage ->private fields.
>
> Closes: https://lore.kernel.org/linux-mm/1707814102-22682-1-git-send-email-quic_charante@quicinc.com/
> Fixes: 616b8371539a ("mm: thp: enable thp migration in generic path")
> Signed-off-by: Zi Yan <ziy@nvidia.com>
> Acked-by: David Hildenbrand <david@redhat.com>

Tested this patch for 6.1 kernel and observed no issues. With that,

Reported-and-tested-by: Charan Teja Kalla <quic_charante@quicinc.com>

Thanks,
Charan