From nobody Sat Feb 7 05:01:20 2026 Received: from mail-pg1-f179.google.com (mail-pg1-f179.google.com [209.85.215.179]) (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 BE606274B2A for ; Wed, 22 Oct 2025 15:33:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.215.179 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761147190; cv=none; b=ZeALcPcIjwafFkZGZt11gRIks8IQnmwXS/vUq0NLo94JGH5fRkemQqtfO5pZqT6jjrQhk9hKsjLcQgIeLhhpr4TCEqqN+HVl2cq4/7uECauBSFDhvPwcNc6z/HW0rMrYZ+3xDmlK0LLE/ZHfokGiQ7Gj0qtuThvtlXd2bOv+w1w= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761147190; c=relaxed/simple; bh=sp2jxQNYf3dyEV6Ht1dZIFg/5isuDrEtnNm4o3HOdu8=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=jcSoDReP202BMxXINQmQy4EuQODWrgENoHt/hMWP+xlHUJ12nFVOieOlZBfG0Z4Cq3EIPBgGfCwtffoI0QR7kMiYrCA1JApgdzPMT4OO+Mb4BvQ62SQ7s3PmfFYyVAhbfsPU8b81LWiRY+6mUpHJNa2LtcKenIT+fQ8tL8xiQNw= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=GhweH1Zo; arc=none smtp.client-ip=209.85.215.179 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="GhweH1Zo" Received: by mail-pg1-f179.google.com with SMTP id 41be03b00d2f7-b6cea7c527bso529610a12.3 for ; Wed, 22 Oct 2025 08:33:05 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1761147185; x=1761751985; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=bZVnN7fp0G3FFsg6wsk/hleC1984NY97+iWMyaKEDz8=; b=GhweH1ZonZ96nrRuCRk0iq/DrjFjMxSUVbQBDE5gfJLDVV2s9LJwAh1m4MKL4TXKEy olWmx27y0x0SFmAJ45RwLB7r0kgZAQgkKVs3qsCNHDWTSEuarG7Uv86M/Ay/4BNS9blI pRRfEiqkH+RDgfPKvTnRFAjD9BZ/iJTlX2V46rsPyQSxCPD3sbiB3Ykde02t1s60+JBy zpQ8ruzYrYCHny8JgVo7lNJ0bMTAyAAchO+7CXFdrZJQkye1Bza2vQ4Sp24/QogfpCkX 2Gw/oKrxmSYTlRxNBFhZDhjf6qlxfv58/HLruUzw40QywsXTEOXAuEP/QEBkrlANNflG x8kw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1761147185; x=1761751985; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=bZVnN7fp0G3FFsg6wsk/hleC1984NY97+iWMyaKEDz8=; b=ppOm+OV3nNbaJ+B6cjcdanJiIniGDhsPwpLzLX4h7H2a+iUH+zSQWuAMuhmEHZ9j6c 8s4jirh7j1RKsImwWXYinYJ1cT5N1GGE2cUGPq9hg2ttTwumPbdqQYf9+zkaGXIpQpFP p7O56U7YYleijgHIrqFg+Skoqk64t99/EnMO3+75wK2KfSb4t50zItRdM39ZUQxncg4H Z/4a+EaBRlPwXG2j9zz1AfT6hzh9t9lrEdBGzWxRpq//h1vtpiXjh0jnQog0oEzy1qCx 2YOwl7mPrP7GZqrkC70E1lHtLHcb0+6Rkjt7ghxGrNcKX29TTEcCr1gre5FtBfsjLmM9 OYYA== X-Forwarded-Encrypted: i=1; AJvYcCVtbARE6wBZqoqytszSMk2eGWOzGhgDMDXXI67r5vl5/zsyZll83uRiP/Hs8TfmKRc6PypJ5VncIK+IBiE=@vger.kernel.org X-Gm-Message-State: AOJu0YxLTxYR8BPZ9e5o3LGWvF76mkyW6nnjF7vT42aknyMgenYFVxeG jUayVDWrr1QjTls2wg7ihTFBqNm36ksbU9L7ek192MPU+FpTFEfcUR8k X-Gm-Gg: ASbGnctE3k3izbwCPnP7DdG9yrfYz6juEm9uvC7wqoKSHR77nGDiZ0tsUPlQrIwkTIT 08StY9eIWypyQ0EOhHEOLhtq27TfQ4yfzVmHZCd2YBMR7pcVCHzb1AE++qLT5yCyLOfnmDxNNXd K1YuVNmasefeC9SN7+98OsmSPi0vJBZ/JNm/dJjyQVQobdZ8JJcvtyV/83vHXyCvYU5PI6K5xw2 1qqO7xQEOkZO5fNQEuFkWyvaL4KtZDt8XyZLgeCWBFA4EACFSyANcYJaDPeZhoy26cRE2mX5N6e wnh0ZWAB2gFIWEayLDTpV2WIV/RVbJC3XciymBse6jS5BKx8Mg1B4HpfWjfy7BZwOzaSpftFWYx JU+QyMsoGH2e8epq3xov3pD5YQKXctVAxVDifZ+VqMbbBy54Nq40CKyuliIJxsBJ4CXAKSW2sTB gXUou5T3dPG+M/Tq1+oH1E7zpcOtmicOAj63jrnw== X-Google-Smtp-Source: AGHT+IGQkq0z/ZJ+qpM4UMe4gES4ssp4l9ztDVvOS3jum1ycvFbCo7Cw2cmJSkRbFVsQ3smyxo4c4w== X-Received: by 2002:a17:903:46c7:b0:274:aab9:4ed4 with SMTP id d9443c01a7336-290cb65f861mr280258655ad.57.1761147184829; Wed, 22 Oct 2025 08:33:04 -0700 (PDT) Received: from weg-ThinkPad-P16v-Gen-2.. ([2804:30c:166c:ce00:98e6:668e:c32f:8f4]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-292471fde15sm142097195ad.84.2025.10.22.08.33.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 22 Oct 2025 08:33:04 -0700 (PDT) From: Pedro Demarchi Gomes To: David Hildenbrand , Andrew Morton Cc: Xu Xin , Chengming Zhou , craftfever , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Pedro Demarchi Gomes Subject: [PATCH v4] ksm: use range-walk function to jump over holes in scan_get_next_rmap_item Date: Wed, 22 Oct 2025 12:30:59 -0300 Message-ID: <20251022153059.22763-1-pedrodemargomes@gmail.com> X-Mailer: git-send-email 2.43.0 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" Currently, scan_get_next_rmap_item() walks every page address in a VMA to locate mergeable pages. This becomes highly inefficient when scanning large virtual memory areas that contain mostly unmapped regions. This patch replaces the per-address lookup with a range walk using walk_page_range(). The range walker allows KSM to skip over entire unmapped holes in a VMA, avoiding unnecessary lookups. This problem was previously discussed in [1]. [1] https://lore.kernel.org/linux-mm/423de7a3-1c62-4e72-8e79-19a6413e420c@r= edhat.com/ Reported-by: craftfever Suggested-by: David Hildenbrand --- v4: - Make minimal changes to replace folio_walk by walk_page_range_vma v3: https://lore.kernel.org/all/20251016012236.4189-1-pedrodemargomes@gmail= .com/ - Treat THPs in ksm_pmd_entry - Update ksm_scan.address outside walk_page_range - Change goto to while loop v2: https://lore.kernel.org/all/20251014151126.87589-1-pedrodemargomes@gmai= l.com/ - Use pmd_entry to walk page range - Use cond_resched inside pmd_entry() - walk_page_range returns page+folio v1: https://lore.kernel.org/all/20251014055828.124522-1-pedrodemargomes@gma= il.com/ Reported-by: craftfever Closes: https://lkml.kernel.org/r/020cf8de6e773bb78ba7614ef250129f11a63781@= murena.io Suggested-by: David Hildenbrand Co-developed-by: David Hildenbrand Signed-off-by: David Hildenbrand Fixes: 31dbd01f3143 ("ksm: Kernel SamePage Merging") Signed-off-by: Pedro Demarchi Gomes --- mm/ksm.c | 113 ++++++++++++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 104 insertions(+), 9 deletions(-) diff --git a/mm/ksm.c b/mm/ksm.c index 3aed0478fdce..4f672f4f2140 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -2455,6 +2455,95 @@ static bool should_skip_rmap_item(struct folio *foli= o, return true; } =20 +struct ksm_next_page_arg { + struct folio *folio; + struct page *page; + unsigned long addr; +}; + +static int ksm_next_page_pmd_entry(pmd_t *pmdp, unsigned long addr, unsign= ed long end, + struct mm_walk *walk) +{ + struct ksm_next_page_arg *private =3D walk->private; + struct vm_area_struct *vma =3D walk->vma; + pte_t *start_ptep =3D NULL, *ptep, pte; + struct mm_struct *mm =3D walk->mm; + struct folio *folio; + struct page *page; + spinlock_t *ptl; + pmd_t pmd; + + if (ksm_test_exit(mm)) + return 0; + + cond_resched(); + + pmd =3D pmdp_get_lockless(pmdp); + if (!pmd_present(pmd)) + return 0; + + if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && pmd_leaf(pmd)) { + ptl =3D pmd_lock(mm, pmdp); + pmd =3D pmdp_get(pmdp); + + if (!pmd_present(pmd)) { + goto not_found_unlock; + } else if (pmd_leaf(pmd)) { + page =3D vm_normal_page_pmd(vma, addr, pmd); + if (!page) + goto not_found_unlock; + folio =3D page_folio(page); + + if (folio_is_zone_device(folio) || !folio_test_anon(folio)) + goto not_found_unlock; + + page +=3D ((addr & (PMD_SIZE - 1)) >> PAGE_SHIFT); + goto found_unlock; + } + spin_unlock(ptl); + } + + start_ptep =3D pte_offset_map_lock(mm, pmdp, addr, &ptl); + if (!start_ptep) + return 0; + + for (ptep =3D start_ptep; addr < end; ptep++, addr +=3D PAGE_SIZE) { + pte =3D ptep_get(ptep); + + if (!pte_present(pte)) + continue; + + page =3D vm_normal_page(vma, addr, pte); + if (!page) + continue; + folio =3D page_folio(page); + + if (folio_is_zone_device(folio) || !folio_test_anon(folio)) + continue; + goto found_unlock; + } + +not_found_unlock: + spin_unlock(ptl); + if (start_ptep) + pte_unmap(start_ptep); + return 0; +found_unlock: + folio_get(folio); + spin_unlock(ptl); + if (start_ptep) + pte_unmap(start_ptep); + private->page =3D page; + private->folio =3D folio; + private->addr =3D addr; + return 1; +} + +static struct mm_walk_ops ksm_next_page_ops =3D { + .pmd_entry =3D ksm_next_page_pmd_entry, + .walk_lock =3D PGWALK_RDLOCK, +}; + static struct ksm_rmap_item *scan_get_next_rmap_item(struct page **page) { struct mm_struct *mm; @@ -2542,21 +2631,27 @@ static struct ksm_rmap_item *scan_get_next_rmap_ite= m(struct page **page) ksm_scan.address =3D vma->vm_end; =20 while (ksm_scan.address < vma->vm_end) { + struct ksm_next_page_arg ksm_next_page_arg; struct page *tmp_page =3D NULL; - struct folio_walk fw; struct folio *folio; =20 if (ksm_test_exit(mm)) break; =20 - folio =3D folio_walk_start(&fw, vma, ksm_scan.address, 0); - if (folio) { - if (!folio_is_zone_device(folio) && - folio_test_anon(folio)) { - folio_get(folio); - tmp_page =3D fw.page; - } - folio_walk_end(&fw, vma); + int found; + + found =3D walk_page_range_vma(vma, ksm_scan.address, + vma->vm_end, + &ksm_next_page_ops, + &ksm_next_page_arg); + + if (found > 0) { + folio =3D ksm_next_page_arg.folio; + tmp_page =3D ksm_next_page_arg.page; + ksm_scan.address =3D ksm_next_page_arg.addr; + } else { + VM_WARN_ON_ONCE(found < 0); + ksm_scan.address =3D vma->vm_end - PAGE_SIZE; } =20 if (tmp_page) { --=20 2.43.0