From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta0.migadu.com (out-110.mta0.migadu.com [91.218.175.110]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 90D7D47278D for ; Tue, 18 Aug 2026 13:12:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.110 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787058745; cv=none; b=aMoeaqy5gKTZVC4NRjrF1+hAEQPKLoiMb33hwtPMj1oB8CTkIXPaphdiYg2PIpmMeZnXqD2xqzeLgI5Yi/iB8X4f702y6KhIf/wF+GMCkBsPZu0EH/Di5mFeFncCg+Q0FEE5/wLWhHEGTcdVUuAHUh9SV4hyqFjvZg+e2DGPxKU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787058745; c=relaxed/simple; bh=1Dz5t2k/qHsfuuzKgM9VwuvNQXNi7pjePtn1+ZkgY2I=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=XHZtZQt2NzDwR+USXVUPg+otQjDABZqD6ZpvRueeR0m0gWybI6MFTIwposBHLDRblveLvYaVNRUeeUyCTyKMbKSP4a7AeLHENleh6fIFgZhdXeU2DJk5+JCi9NQZm5lC2V9ExgInpo8VhB10EpQvw0hnHfzqB+X7eWag2FbWce0= 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=ePR1CsFS; arc=none smtp.client-ip=91.218.175.110 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="ePR1CsFS" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=1Dz5t2k/qHsfuuzKgM9VwuvNQXNi7pjePtn1+ZkgY2I=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1787058741; v=1; x=1787663541; b=ePR1CsFSfhtZnZDwdzp278rbXm8Fa/19ikhEl7qhC9YsSoeftTdy+Lf6sIPvRiKMyN1OB208 DTU5CEAEzL+MTIT3nlp1lfEVSmD0gQu61fhKKMUP+r7SWZ4IvXz7XZVKBeflgERBPyvmBtrjFYt u3wJ9i5U9DwEHpNIK9QKyAXs= X-Envelope-To: linux-kernel@vger.kernel.org Received: from localhost (2a03:2880:10ff:48::) by mta11.migadu.com with ESMTPS id 841d0e040e1652fc; Tue, 18 Aug 2026 13:12:21 +0000 X-Migadu-Flow: FLOW_OUT 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, Nico Pache , Liam R. Howlett , ryan.roberts@arm.com, Vlastimil Babka , lance.yang@linux.dev, linux-kernel@vger.kernel.org, nphamcs@gmail.com, shikemeng@huaweicloud.com, yosry@kernel.org, kernel-team@meta.com, Usama Arif Subject: [PATCH v6 03/12] mm: add PMD swap entry splitting support Date: Tue, 18 Aug 2026 06:09:44 -0700 Message-ID: <20260818131202.494754-4-usama.arif@linux.dev> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260818131202.494754-1-usama.arif@linux.dev> References: <20260818131202.494754-1-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 Add a swap branch in __split_huge_pmd_locked() that splits a PMD swap entry into 512 PTE swap entries. No folio reference is needed because swap entries point to swap slots rather than pages. Each PTE inherits the correct sub-slot offset and preserves soft_dirty, uffd_wp, and exclusive flags. The folio_remove_rmap_pmd() gate at the end must inspect old_pmd rather than *pmd: for a present THP split, *pmd has already been cleared by pmdp_invalidate(), and that invalidated bit pattern can decode as a plausible swap entry. 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 | 29 ++++++++++++++++++++++++++++- 1 file changed, 28 insertions(+), 1 deletion(-) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 1b6b0aa2baa3b..a473e85d30f51 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -3252,6 +3252,14 @@ 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); + /* Swap entries have no page for the migration freeze path. */ + freeze = false; + old_pmd = *pmd; + soft_dirty = pmd_swp_soft_dirty(old_pmd); + uffd_wp = pmd_swp_uffd(old_pmd); + anon_exclusive = pmd_swp_exclusive(old_pmd); } else { /* * Up to this point the pmd is present and huge and userland has @@ -3388,6 +3396,25 @@ 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(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; @@ -3415,7 +3442,7 @@ 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(old_pmd) && !pmd_is_swap_entry(old_pmd)) folio_remove_rmap_pmd(folio, page, vma); if (freeze) put_page(page); -- 2.53.0-Meta