Re: [PATCH 2/8] mm/huge_memory: use folio_swap_entry() when splitting a swapcache folio
From: "Zi Yan" <ziy@nvidia.com>
Date: 2026-08-31 14:50:47
Also in:
linux-mm, lkml
On Sun Aug 30, 2026 at 6:32 AM EDT, Tal Zussman wrote:
quoted hunk ↗ jump to hunk
__split_folio_to_order() open-codes the swap entry computation for the split-out folios. Use folio_swap_entry() instead. No functional change. Signed-off-by: Tal Zussman <redacted> --- mm/huge_memory.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 54494c3fa983..03287f995d92 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c@@ -3760,7 +3760,7 @@ static void __split_folio_to_order(struct folio *folio, int old_order, VM_WARN_ON_ONCE_PAGE(new_folio->private, new_head); if (folio_test_swapcache(folio)) - new_folio->swap.val = folio->swap.val + i; + new_folio->swap = folio_swap_entry(folio, i);
folio_swap_entry() checks folio_nr_pages(folio) internally. folio->_nr_pages is in first tail page of folio. If new_order is 0, it is basically checking memcg_data in the first new_folio. And after first iteration, folio->_nr_page will be clobbered. Without NR_PAGES_IN_LARGE_FOLIO, folio_nr_pages() is derived from folio_order(), which is in folio->_flags_1. It can have the same issue. Please keep it open coded. You can add a comment like "during split, not all folio fields are avaialbe, open code the swap calculation".
/* Page flags must be visible before we make the page non-compound. */ smp_wmb();
-- Best Regards, Yan, Zi