From nobody Mon Oct 6 11:57:05 2025 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id AE7FA1E8320 for ; Tue, 22 Jul 2025 15:06:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753196787; cv=none; b=Jg5bws1Z34KN37Pv3xTuYPz/H+Chbg11msuHaRUgfGqIa1YVUEF0tC01rgfQwlUptCO72F+qMehkdrjGjPbnCBVOIrCY4g21TBRJwTsm1wz9Fg5hw39gEExYMlqVj7iPdbP7vdjCDxP85AhZE7Vu/gFzjCzDvazAf1V3uB3xaFA= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753196787; c=relaxed/simple; bh=t9/tPmYresC045E3z38JghIzYZjCr3lnQYnP61HpYWU=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=QTupzy2j/Nc7MQRcIYP1vn9vW1822qTJuo3eL47WS/eWOvIgGs/Fv6fPMpcYIfABTD3acVpRya2d5IDOy5BWRrrvItzb1+6NIm8E9KnwcDHJIX8ufAB7y7u2ePtkc2Ab7ZH9j/bkrQJNtvDhTqhi/SS6N/fYOsWDm/hkgYZdxWk= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 73E59152B; Tue, 22 Jul 2025 08:06:19 -0700 (PDT) Received: from localhost.localdomain (unknown [10.163.92.223]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id EFB1F3F6A8; Tue, 22 Jul 2025 08:06:20 -0700 (PDT) From: Dev Jain To: akpm@linux-foundation.org, david@redhat.com Cc: ziy@nvidia.com, baolin.wang@linux.alibaba.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, baohua@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Dev Jain Subject: [PATCH v3 2/3] khugepaged: Optimize __collapse_huge_page_copy_succeeded() by PTE batching Date: Tue, 22 Jul 2025 20:35:58 +0530 Message-Id: <20250722150559.96465-3-dev.jain@arm.com> X-Mailer: git-send-email 2.39.5 (Apple Git-154) In-Reply-To: <20250722150559.96465-1-dev.jain@arm.com> References: <20250722150559.96465-1-dev.jain@arm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Use PTE batching to optimize __collapse_huge_page_copy_succeeded(). On arm64, suppose khugepaged is scanning a pte-mapped 2MB THP for collapse. Then, calling ptep_clear() for every pte will cause a TLB flush for every contpte block. Instead, clear_ptes() does a contpte_try_unfold_partial() which will flush the TLB only for the (if any) starting and ending contpte block, if they partially overlap with the range khugepaged is looking at. For all arches, there should be a benefit due to batching atomic operations on mapcounts due to folio_remove_rmap_ptes() and saving some calls. Signed-off-by: Dev Jain Acked-by: David Hildenbrand Reviewed-by: Baolin Wang --- mm/khugepaged.c | 25 ++++++++++++++++++------- 1 file changed, 18 insertions(+), 7 deletions(-) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index a55fb1dcd224..63517ef7eafb 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -700,12 +700,15 @@ static void __collapse_huge_page_copy_succeeded(pte_t= *pte, spinlock_t *ptl, struct list_head *compound_pagelist) { + unsigned long end =3D address + HPAGE_PMD_SIZE; struct folio *src, *tmp; - pte_t *_pte; pte_t pteval; + pte_t *_pte; + int nr_ptes; =20 - for (_pte =3D pte; _pte < pte + HPAGE_PMD_NR; - _pte++, address +=3D PAGE_SIZE) { + for (_pte =3D pte; _pte < pte + HPAGE_PMD_NR; _pte +=3D nr_ptes, + address +=3D nr_ptes * PAGE_SIZE) { + nr_ptes =3D 1; pteval =3D ptep_get(_pte); if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1); @@ -722,18 +725,26 @@ static void __collapse_huge_page_copy_succeeded(pte_t= *pte, struct page *src_page =3D pte_page(pteval); =20 src =3D page_folio(src_page); - if (!folio_test_large(src)) + + if (folio_test_large(src)) { + int max_nr_ptes =3D (end - address) >> PAGE_SHIFT; + + nr_ptes =3D folio_pte_batch(src, _pte, pteval, max_nr_ptes); + } else { release_pte_folio(src); + } + /* * ptl mostly unnecessary, but preempt has to * be disabled to update the per-cpu stats * inside folio_remove_rmap_pte(). */ spin_lock(ptl); - ptep_clear(vma->vm_mm, address, _pte); - folio_remove_rmap_pte(src, src_page, vma); + clear_ptes(vma->vm_mm, address, _pte, nr_ptes); + folio_remove_rmap_ptes(src, src_page, nr_ptes, vma); spin_unlock(ptl); - free_folio_and_swap_cache(src); + free_swap_cache(src); + folio_put_refs(src, nr_ptes); } } =20 --=20 2.30.2