From c262ffd72c8539d16ada8641a6348c5a88f0c542 Mon Sep 17 00:00:00 2001 From: Kairui Song Date: Mon, 28 Jul 2025 15:53:01 +0800 Subject: [PATCH] mm/shmem, swap: tidy up THP swapin checks Move all THP swapin related checks under CONFIG_TRANSPARENT_HUGEPAGE, so they will be trimmed off by the compiler if not needed. And add a WARN if shmem sees a order > 0 entry when CONFIG_TRANSPARENT_HUGEPAGE is disabled, that should never happen unless things went very wrong. There should be no observable feature change except the new added WARN. Link: https://lkml.kernel.org/r/20250728075306.12704-4-ryncsn@gmail.com Signed-off-by: Kairui Song Reviewed-by: Baolin Wang Cc: Baoquan He Cc: Barry Song Cc: Chris Li Cc: Dev Jain Cc: Hugh Dickins Cc: Kemeng Shi Cc: Matthew Wilcox (Oracle) Cc: Nhat Pham Signed-off-by: Andrew Morton --- mm/shmem.c | 39 ++++++++++++++++++--------------------- 1 file changed, 18 insertions(+), 21 deletions(-) diff --git a/mm/shmem.c b/mm/shmem.c index 6e00d2ec40a9..88058d53ae55 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -2017,26 +2017,38 @@ static struct folio *shmem_swap_alloc_folio(struct inode *inode, swp_entry_t entry, int order, gfp_t gfp) { struct shmem_inode_info *info = SHMEM_I(inode); + int nr_pages = 1 << order; struct folio *new; void *shadow; - int nr_pages; /* * We have arrived here because our zones are constrained, so don't * limit chance of success with further cpuset and node constraints. */ gfp &= ~GFP_CONSTRAINT_MASK; - if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && order > 0) { - gfp_t huge_gfp = vma_thp_gfp_mask(vma); + if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) { + if (WARN_ON_ONCE(order)) + return ERR_PTR(-EINVAL); + } else if (order) { + /* + * If uffd is active for the vma, we need per-page fault + * fidelity to maintain the uffd semantics, then fallback + * to swapin order-0 folio, as well as for zswap case. + * Any existing sub folio in the swap cache also blocks + * mTHP swapin. + */ + if ((vma && unlikely(userfaultfd_armed(vma))) || + !zswap_never_enabled() || + non_swapcache_batch(entry, nr_pages) != nr_pages) + return ERR_PTR(-EINVAL); - gfp = limit_gfp_mask(huge_gfp, gfp); + gfp = limit_gfp_mask(vma_thp_gfp_mask(vma), gfp); } new = shmem_alloc_folio(gfp, order, info, index); if (!new) return ERR_PTR(-ENOMEM); - nr_pages = folio_nr_pages(new); if (mem_cgroup_swapin_charge_folio(new, vma ? vma->vm_mm : NULL, gfp, entry)) { folio_put(new); @@ -2320,9 +2332,6 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index, /* Look it up and read it in.. */ folio = swap_cache_get_folio(swap, NULL, 0); if (!folio) { - int nr_pages = 1 << order; - bool fallback_order0 = false; - /* Or update major stats only when swapin succeeds?? */ if (fault_type) { *fault_type |= VM_FAULT_MAJOR; @@ -2330,20 +2339,8 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index, count_memcg_event_mm(fault_mm, PGMAJFAULT); } - /* - * If uffd is active for the vma, we need per-page fault - * fidelity to maintain the uffd semantics, then fallback - * to swapin order-0 folio, as well as for zswap case. - * Any existing sub folio in the swap cache also blocks - * mTHP swapin. - */ - if (order > 0 && ((vma && unlikely(userfaultfd_armed(vma))) || - !zswap_never_enabled() || - non_swapcache_batch(swap, nr_pages) != nr_pages)) - fallback_order0 = true; - /* Skip swapcache for synchronous device. */ - if (!fallback_order0 && data_race(si->flags & SWP_SYNCHRONOUS_IO)) { + if (data_race(si->flags & SWP_SYNCHRONOUS_IO)) { folio = shmem_swap_alloc_folio(inode, vma, index, swap, order, gfp); if (!IS_ERR(folio)) { skip_swapcache = true; -- 2.47.2