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Wed, 01 Jul 2026 04:47:32 -0700 (PDT) Received: from localhost.localdomain ([2607:f130:0:11a::31]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-30ee327cea7sm22518169eec.31.2026.07.01.04.47.28 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Wed, 01 Jul 2026 04:47:32 -0700 (PDT) From: wang lian To: damon@lists.linux.dev, linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, sj@kernel.org, gutierrez.asier@huawei-partners.com, daichaobing@sangfor.com.cn, lianux.wang@processmission.com, Wang Lian , Kunwu Chan Subject: [PATCH v2 2/5] mm/khugepaged: add damon_collapse_folio_range() for external callers Date: Wed, 1 Jul 2026 19:47:13 +0800 Message-ID: <20260701114716.56503-3-lianux.mm@gmail.com> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20260701114716.56503-1-lianux.mm@gmail.com> References: <20260701114716.56503-1-lianux.mm@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 9EC7FC0004 X-Rspam-User: X-Stat-Signature: kqejpuk9zrqogj34be1gmyx9wdbj1ckf X-HE-Tag: 1782906453-242344 X-HE-Meta: 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 PkpAJB0X 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: Wang Lian 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: Wang Lian Signed-off-by: Wang Lian --- include/linux/khugepaged.h | 3 +++ mm/khugepaged.c | 39 ++++++++++++++++++++++++++++++++++++++ 2 files changed, 42 insertions(+) diff --git a/include/linux/khugepaged.h b/include/linux/khugepaged.h index d7a9053ff4fe..6fb8a6857790 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)) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 617bca76db49..0387841ba2e7 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -3272,3 +3272,42 @@ 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 = { + .is_khugepaged = false, + }; + 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; + + result = collapse_huge_page(mm, start_addr, 1, 0, &cc, target_order); + if (result == SCAN_SUCCEED) + return 0; + return madvise_collapse_errno(result); +} +EXPORT_SYMBOL_GPL(damon_collapse_folio_range); -- 2.50.1 (Apple Git-155)