From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-177.mta0.migadu.com (out-177.mta0.migadu.com [91.218.175.177]) (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 BA4A842DA47 for ; Mon, 13 Jul 2026 13:36:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.177 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783949796; cv=none; b=AF7Z2pgRF9C2N3XPCtegHoOMa2DR+4TG1MvUjJXSBtcFfdbWQtMkcw1nPi+GVtIkWMkakyU0eaoXcRTuMZcrYq9HUcBGFfSi4fSLmlPEgWENK2S+y7doJe2n1lJnqZINFnE/ZOnbbe4js8IB6a6AA1btM6R/xFDqCO2ynw2+QCU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783949796; c=relaxed/simple; bh=+jFyYxKO7p27oyDCYMBlSlBoHCxMm84X/SqyvMXHXs0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=QZ7S80YpKDCYXsKkRQwZuPOozPwBSB6+PTbRfDJ0FmTZaBdDAwCt1MRk377uUVap6ENn3tYbbne7JcdyQbSk09+fCfteGOMT+g184wnrSVkXNVaxSJcGbU0nZIYhRQiqDcOk05Ds5M+w+DKdqdypWt1K3dBCrxJwObzWARJbcq8= 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=M7MNGg3Q; arc=none smtp.client-ip=91.218.175.177 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="M7MNGg3Q" 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=1783949792; 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=zUERJd2UgNsh+Iab1xJmAl5cWHaF6LdlBWi3pKgh33Y=; b=M7MNGg3QmSrpvjpN81xLgRREOq5NGH5mBPFZVto+uLgOuCYdeOMhbgRXRN8URC53lOHyp5 xTHp2tF/E2JmUwM8Ogg/ImqQw8ns/f8O1HtWB05FN2s/0t0aonKnK6f4KdabnYkWhpivjb I5Z9jNuzu7w+Rv4/ehVDrG3fGJZ8xJk= 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, yosry@kernel.org, kernel-team@meta.com, Usama Arif Subject: [PATCH v4 02/11] mm: add PMD swap entry splitting support Date: Mon, 13 Jul 2026 06:35:37 -0700 Message-ID: <20260713133613.2707815-3-usama.arif@linux.dev> In-Reply-To: <20260713133613.2707815-1-usama.arif@linux.dev> References: <20260713133613.2707815-1-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. 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() by the time the gate runs, and the invalidated bit pattern can decode as a plausible swap entry via softleaf_from_pmd() (any type_num < MAX_SWAPFILES reads as SWAP). 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 0dc6d630570f..e602cf2b48db 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -3208,6 +3208,12 @@ 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 @@ -3344,6 +3350,25 @@ 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; @@ -3371,7 +3396,7 @@ 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