From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-185.mta0.migadu.com (out-185.mta0.migadu.com [91.218.175.185]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 616C03F5BD3 for ; Tue, 2 Jun 2026 14:26:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.185 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780410405; cv=none; b=qgPb+L9iM55rwl9WmqYH1KuJ6DQS4V7GDgfO4nToeWGdES6l/INQux9l6GzO6wYirIjvRGYaK1DuM4YVqKp6Mr6DyaFtkQJc8Wr8C+kHVTrCame5tLmoVul2Co00NscZs8Gg2iNT0o7/3fdNYJCE3PvF9DeFyOmUv4gxvFoaZIE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780410405; c=relaxed/simple; bh=g8fXFVvJ0sBwhRN4cmWnUh3DT3FnZaQP4kruSTH5CgM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=tA1wxHxk9I405xZmS/UCE7urUudRMvNuZazLoJGSkHMYSfhv9rGuHbuwgQYF+shx8Si0K6P9mB8UNgjx5FmS9yeljoev+uD/3xa4k5Pe6PLL1OsxUKIslfotyBFqmAKzVhMZS44fA5MSW/1Epfx7rtKDl84TWcS3pr1mnEcdLGk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=OSwv9tii; arc=none smtp.client-ip=91.218.175.185 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="OSwv9tii" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1780410402; 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=UoRYKXRwctRxeiN8IuNvbapEIDidQ7fOG8OMVHSTk9c=; b=OSwv9tiieOZAw8uPxayyWCtZQKicqUWhHhLedJmLmiqEIUkciBN9wm/QHQLU2gM1YTlgXj wp8GvYuT9Qea5XT4j9jwxI2neJ4zW4n9wSIlUKt3ZAnCdTnd4tw78aJn1zz8tm619kr4QB Upq9B7LTov4H9OqWzUrYWb1BDzd5nBM= From: Usama Arif To: Andrew Morton , david@kernel.org, chrisl@kernel.org, kasong@tencent.com, ljs@kernel.org, ziy@nvidia.com 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: [v2 08/16] mm: add PMD swap entry splitting support Date: Tue, 2 Jun 2026 07:24:16 -0700 Message-ID: <20260602142537.198755-9-usama.arif@linux.dev> In-Reply-To: <20260602142537.198755-1-usama.arif@linux.dev> References: <20260602142537.198755-1-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 af6a9c20131a..7cb1afde46e1 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -3144,6 +3144,12 @@ 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 @@ -3280,6 +3286,25 @@ 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; @@ -3303,7 +3328,7 @@ 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); -- 2.52.0