On 2/28/2025 9:12 PM, Zi Yan wrote:
> Pagecache uses multi-index entries for large folio, so does shmem. Only
> swap cache still stores multiple entries for a single large folio.
> Commit fc346d0a70a1 ("mm: migrate high-order folios in swap cache correctly")
> fixed swap cache but got shmem wrong by storing multiple entries for
> a large shmem folio. Fix it by storing a single entry for a shmem
> folio.
>
> Fixes: fc346d0a70a1 ("mm: migrate high-order folios in swap cache correctly")
> Reported-by: Liu Shixin <liushixin2@xxxxxxxxxx>
> Closes: https://lore.kernel.org/all/28546fb4-5210-bf75-16d6-43e1f8646080@xxxxxxxxxx/
> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
> ---
> mm/migrate.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 365c6daa8d1b..9db26f5527a8 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -44,6 +44,7 @@
> #include <linux/sched/sysctl.h>
> #include <linux/memory-tiers.h>
> #include <linux/pagewalk.h>
> +#include <linux/shmem_fs.h>
>
> #include <asm/tlbflush.h>
>
> @@ -524,7 +525,11 @@ static int __folio_migrate_mapping(struct address_space *mapping,
> folio_set_swapcache(newfolio);
> newfolio->private = folio_get_private(folio);
> }
> - entries = nr;
> + /* shmem uses high-order entry */
> + if (shmem_mapping(mapping))
> + entries = 1;
> + else
> + entries = nr;
LGTM functionally.
As a minor style suggestion, can we consider using a ternary operator:
entries = shmem_mapping(mapping) ? 1 : nr; /* shmem uses high-order entry */
This looks cleaner to me.
Reviewed-by: Shivank Garg <shivankg@xxxxxxx>
> } else {
> VM_BUG_ON_FOLIO(folio_test_swapcache(folio), folio);
> entries = 1;
