From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f169.google.com (mail-pl1-f169.google.com [209.85.214.169]) (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 33F3F47CC83 for ; Thu, 2 Jul 2026 09:46:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.169 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782985606; cv=none; b=uc9kzagIaZSmnIpK8E0/61mbjLRje8oZ6/J2G2/n/NwVnWSS6IR8HLU/DHqXDaKhuui060aftWFiADqffwDWeqED73dWw8nIe3mGwZbcU2P93LaN6gs056izq+c2S046jyPXOdkIO5wV7DQhdyPIlIGBJMQ+PggTQ9YG/6Xu/LA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782985606; c=relaxed/simple; bh=JwJSC6QBIXHZ6EVUA6kz1vznH9OKSQxIf7AtLS4NMYQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=pCW0M4NcqCwaO3szBatX6Of0l7oYtUVd5rfKXM7e08B/nuPaaCnX7KJS7XssZOJh1XirzzdFhxZ4RkJmItqHVM/eeZ8A1hT+T5gDKhGmludOOCNvdrsYOP/hagE4YCzmEibvHixICFJHZ6vbF5gAfAB2yx55XTyuAQFk0dZ1hjc= 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=lHnE+Qvb; arc=none smtp.client-ip=209.85.214.169 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="lHnE+Qvb" Received: by mail-pl1-f169.google.com with SMTP id d9443c01a7336-2c7ebfb63c6so12208275ad.3 for ; Thu, 02 Jul 2026 02:46:45 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1782985604; x=1783590404; darn=lists.linux.dev; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=icPP3MmY8t9qE9Xpwb6MvphYCRwC/sqcyq3pTHjWUnM=; b=lHnE+Qvb6OflTpXpWp/4IqvkRXvz5+Vt1QKOK8OnEhh54UCFy9rwNCZnAG11jGTnPB k+JmIz8gm55tVsc8XNhdcMz9p4ZLiIYzU9Fo0BQnGXGPzizzCqWE0Nbe4ardVBUv2ASj k3NYAj/OB5olvFdWonIbcKCk2H7lCkNXQzniWyU9oZcqagk0n1fzDNEqDaSBylM9yDxq rjRbiOuIO60wqKYVnPMDDB+KxSZirul62AW/HEyszdbBVn8/Q3RS3EjCCokg3JSC0NtU bwIZpeb7TKlJkl/sLawUiClY/+DHK8ZyY7C/9K1gsWqG/DIbT8/6mc8V7REFA6MpDDSM wBIQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1782985604; x=1783590404; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-gg:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to; bh=icPP3MmY8t9qE9Xpwb6MvphYCRwC/sqcyq3pTHjWUnM=; b=SsfOUYOPIdu6nTLhR8gupFLxNmxfzEqc28KkvxFRe52hKJQM0p3kgerwl1VtxaOgJ/ u0M0VXdhU/jbu/LR0SFKsS7NbPUIvLNXrZuw7T2JCg/Crhfix/KwEKecoNYYqoXt+Vnq V/KTn1ZlzfzwgmSDZtIJ3jopnLT+mWVOb5HevTAg4h8Jvnmb3yyVog/DK+Z6TJZ3nmbR 5XwtMQ+/hw4b06z07MPK2H+t2JuyzqC815Ge68EAgL47o987kpWDbesd8RYgYRTW3ghA WjCYCM9bHqplEWsv3GlY42IIm1rYKyK4bekcbtwwJq7yQguItqJXbSVvnzawYSaaJOsD nTVw== X-Gm-Message-State: AOJu0YzkyTgMWuoHgiA1mkwOFG3Z9khqe6WS7jtrrIjMU+Uxpn22iF2j 1RVkrwVkDmsVVnFG55TVdJE6Q0GVpolqd0L8Hdrhyl1xeZvEMXMaXtKl X-Gm-Gg: AfdE7cnFqhFZ0fnDsjeC2raUt1npnfna+uqUWVELf9vPMDkKIqWlbyvpJtrUn1GcSUz ZsiFP+6fgS5AZMfWW/wmnhrdOGLWTVu14zIy5jaYZ3QEzXvlXk+qAKJM1XQ7EU9+A6LVlBiG9LF SfNZxNsrOZddgEguq5gwRBcgvFL2nqIO1aGXOPiLnah7Mhl61YSibaZ/MsBY0ojYUrsbT2H1lDc wde8UX/8wC/pdGkrwam/E9qFnatG5Fxc18O4MfG1DyZiRmHCGUnK9gH+XJVFuRslnkeI3mInMEB DSmUcn8CsLo+tNtqRm/g6GPG7Qpui+jAFpbdjH2HmX6n2Qawv+pmD4CL7pM0LIh0o6Qf3SbPtWW mogXjRvlr6IDd6Td6U/DdHW7J7AyYc4j4XpZwWrhXVqBBmbVH96PFh3i+8vzxoPykiEcRuz0+PU jbuA== X-Received: by 2002:a05:6a20:6f93:b0:3bf:9a30:3a12 with SMTP id adf61e73a8af0-3bff4301c4dmr5363264637.50.1782985604293; Thu, 02 Jul 2026 02:46:44 -0700 (PDT) Received: from localhost.localdomain ([2607:f130:0:11a::31]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-30f116065c5sm5261121eec.11.2026.07.02.02.46.42 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Thu, 02 Jul 2026 02:46:44 -0700 (PDT) From: Lian Wang To: sj@kernel.org Cc: damon@lists.linux.dev, linux-mm@kvack.org, daichaobing@sangfor.com.cn, kunwu.chan@gmail.com Subject: [RESEND RFC PATCH v2 2/5] mm/khugepaged: add damon_collapse_folio_range() for external callers Date: Thu, 2 Jul 2026 17:46:30 +0800 Message-ID: <20260702094633.75658-3-lianux.mm@gmail.com> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20260702094633.75658-1-lianux.mm@gmail.com> References: <20260702094633.75658-1-lianux.mm@gmail.com> Precedence: bulk X-Mailing-List: damon@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Export a thin wrapper around collapse_huge_page() that allows external subsystems such as DAMON to trigger THP collapse on a target address range. Currently restricted to PMD order (HPAGE_PMD_ORDER), since collapse_huge_page() does not yet support arbitrary mTHP orders. The restriction can be relaxed when khugepaged gains mTHP support. The caller must hold a reference to @mm. Do not hold mmap lock: collapse_huge_page() acquires mmap_read_lock for validation, releases it, then acquires mmap_write_lock for the actual collapse. Holding an outer mmap_read_lock would cause a self-deadlock when the same thread attempts the inner mmap_write_lock. Co-developed-by: Kunwu Chan Signed-off-by: Kunwu Chan Signed-off-by: Lian Wang Signed-off-by: Lian Wang --- include/linux/khugepaged.h | 9 ++++++++ mm/khugepaged.c | 46 ++++++++++++++++++++++++++++++++++++++ 2 files changed, 55 insertions(+) diff --git a/include/linux/khugepaged.h b/include/linux/khugepaged.h index d7a9053ff4fe..f7d49cba712f 100644 --- a/include/linux/khugepaged.h +++ b/include/linux/khugepaged.h @@ -20,6 +20,9 @@ extern bool current_is_khugepaged(void); void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr, bool install_pmd); +int damon_collapse_folio_range(struct mm_struct *mm, unsigned long start_addr, + unsigned int target_order); + static inline void khugepaged_fork(struct mm_struct *mm, struct mm_struct *oldmm) { if (mm_flags_test(MMF_VM_HUGEPAGE, oldmm)) @@ -47,6 +50,12 @@ static inline void collapse_pte_mapped_thp(struct mm_struct *mm, { } +static inline int damon_collapse_folio_range(struct mm_struct *mm, + unsigned long start_addr, unsigned int target_order) +{ + return -EINVAL; +} + static inline void khugepaged_min_free_kbytes_update(void) { } diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 617bca76db49..7fe9ce1e0533 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -3272,3 +3272,49 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, return thps == ((hend - hstart) >> HPAGE_PMD_SHIFT) ? 0 : madvise_collapse_errno(last_fail); } + +/** + * damon_collapse_folio_range() - Collapse base pages in range into a THP + * @mm: mm_struct of the target process + * @start_addr: start address (must be order-aligned) + * @target_order: page order of the collapse result (currently only + * HPAGE_PMD_ORDER is supported) + * + * Thin wrapper around collapse_huge_page() for external callers such as + * DAMON. The caller must hold a reference to @mm. Do not hold mmap + * lock: collapse_huge_page() acquires mmap_read_lock for validation, + * releases it, then acquires mmap_write_lock for the collapse. Holding + * an outer mmap_read_lock would self-deadlock. + * + * Return: 0 on success, -EINVAL on bad arguments, negative error from + * madvise_collapse_errno() otherwise. + */ +int damon_collapse_folio_range(struct mm_struct *mm, unsigned long start_addr, + unsigned int target_order) +{ + struct collapse_control *cc; + enum scan_result result; + + if (target_order != HPAGE_PMD_ORDER) { + pr_warn_once("%s: only PMD order (%u) is supported, got %u\n", + __func__, HPAGE_PMD_ORDER, target_order); + return -EINVAL; + } + if (start_addr & ((PAGE_SIZE << target_order) - 1)) + return -EINVAL; + + cc = kmalloc_obj(*cc); + if (!cc) + return -ENOMEM; + cc->is_khugepaged = false; + cc->progress = 0; + + lru_add_drain_all(); + + result = collapse_huge_page(mm, start_addr, 1, 0, cc, target_order); + kfree(cc); + if (result == SCAN_SUCCEED || result == SCAN_PMD_MAPPED) + return 0; + return madvise_collapse_errno(result); +} +EXPORT_SYMBOL_GPL(damon_collapse_folio_range);