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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1783100365; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=pW9EcWBKiEFzIBYCM/zNKeXrU1lf4J5AtLZufC1tyqQ=; b=Zo7f1ThAcBbnyAQcXO/+plrAKEWiMXLaHnHmVuh3SXDXEDzJGc//Sy6CgoxXQ+iA19wdg+ 3es40LfRIQipUlY5UXU+OE6aIFzrxbnIBpxGZl0rfwwQ6j7zvrYWyyrP/pmwh5ivfCF38u fRXOObVQrj01VAiPzupLfzQvgHqhu5g= From: Usama Arif To: Andrew Morton , david@kernel.org, chrisl@kernel.org, kasong@tencent.com, ljs@kernel.org, ziy@nvidia.com, linux-mm@kvack.org Cc: ying.huang@linux.alibaba.com, Baoquan He , willy@infradead.org, youngjun.park@lge.com, hannes@cmpxchg.org, riel@surriel.com, shakeel.butt@linux.dev, alex@ghiti.fr, kas@kernel.org, baohua@kernel.org, dev.jain@arm.com, baolin.wang@linux.alibaba.com, npache@redhat.com, Liam R. Howlett , ryan.roberts@arm.com, Vlastimil Babka , lance.yang@linux.dev, linux-kernel@vger.kernel.org, nphamcs@gmail.com, shikemeng@huaweicloud.com, kernel-team@meta.com, Usama Arif Subject: [PATCH v3 02/11] mm: add PMD swap entry splitting support Date: Fri, 3 Jul 2026 10:38:19 -0700 Message-ID: <20260703173903.3789516-3-usama.arif@linux.dev> In-Reply-To: <20260703173903.3789516-1-usama.arif@linux.dev> References: <20260703173903.3789516-1-usama.arif@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT Add a swap branch in __split_huge_pmd_locked() that splits a PMD swap entry into 512 PTE swap entries. Unlike migration splits, no folio reference is needed because swap entries point to swap slots, not pages. Each PTE inherits the correct sub-slot offset and preserves soft_dirty, uffd_wp, and exclusive flags. This branch is reached from the explicit __split_huge_pmd() callers that hit a non-present PMD: partial-range mprotect / munmap, the wp_huge_pmd() PMD-COW fallback, and the swap-in / swapoff fallbacks added in later patches when the cached folio is no longer PMD-sized. page_vma_mapped_walk() does not iterate PMD swap entries, so try_to_unmap_one() and try_to_migrate_one() do not reach this branch and freeze=true cannot occur in this branch today. page and folio are therefore left uninitialized in the swap branch; a VM_WARN_ON_ONCE(freeze) catches any future caller that breaks this invariant before the freeze path dereferences page_to_pfn(page + i) or put_page(page). Signed-off-by: Usama Arif --- mm/huge_memory.c | 27 ++++++++++++++++++++++++++- 1 file changed, 26 insertions(+), 1 deletion(-) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index bdd8635922f9..201193ce0373 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -3143,6 +3143,12 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, folio_add_anon_rmap_ptes(folio, page, HPAGE_PMD_NR, vma, haddr, rmap_flags); } + } else if (pmd_is_swap_entry(*pmd)) { + VM_WARN_ON_ONCE(freeze); + old_pmd = *pmd; + soft_dirty = pmd_swp_soft_dirty(old_pmd); + uffd_wp = pmd_swp_uffd_wp(old_pmd); + anon_exclusive = pmd_swp_exclusive(old_pmd); } else { /* * Up to this point the pmd is present and huge and userland has @@ -3279,6 +3285,25 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, VM_WARN_ON(!pte_none(ptep_get(pte + i))); set_pte_at(mm, addr, pte + i, entry); } + } else if (pmd_is_swap_entry(old_pmd)) { + softleaf_t sl_entry = softleaf_from_pmd(old_pmd); + pte_t swp_pte; + swp_entry_t sub_entry; + + for (i = 0, addr = haddr; i < HPAGE_PMD_NR; + i++, addr += PAGE_SIZE) { + sub_entry = swp_entry(swp_type(sl_entry), + swp_offset(sl_entry) + i); + swp_pte = swp_entry_to_pte(sub_entry); + if (soft_dirty) + swp_pte = pte_swp_mksoft_dirty(swp_pte); + if (uffd_wp) + swp_pte = pte_swp_mkuffd_wp(swp_pte); + if (anon_exclusive) + swp_pte = pte_swp_mkexclusive(swp_pte); + VM_WARN_ON(!pte_none(ptep_get(pte + i))); + set_pte_at(mm, addr, pte + i, swp_pte); + } } else { pte_t entry; @@ -3302,7 +3327,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, } pte_unmap(pte); - if (!pmd_is_migration_entry(*pmd)) + if (!pmd_is_migration_entry(*pmd) && !pmd_is_swap_entry(*pmd)) folio_remove_rmap_pmd(folio, page, vma); if (freeze) put_page(page); -- 2.53.0-Meta