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Fri, 4 Sep 2026 11:10:31 -0400 (EDT) From: Kiryl Shutsemau To: Andrew Morton , David Hildenbrand , Lorenzo Stoakes Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, Zi Yan , Baolin Wang , "Liam R . Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Vlastimil Babka , Jann Horn , "Kiryl Shutsemau (Meta)" Subject: [PATCH 01/12] mm/khugepaged: drop redundant mm_struct pin in madvise_collapse() Date: Fri, 4 Sep 2026 16:10:15 +0100 Message-ID: <1ff754df1d57154e01356f35d72b1cb06c0f8664.1788533997.git.kas@kernel.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: wfhoh5shxfdw1a838rgjs5muw4qiaua9 X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 9C02940008 X-Rspam-User: X-HE-Tag: 1788534632-10415 X-HE-Meta: U2FsdGVkX19LuU0hLBlPaw+nZVIzUgTQWjdlzEy2Hl3siZQ/ngva9rEHS75N4UlRybvVvuJuN+y3dsEHgTKRSzq0ZWgalSRZdoIHW+Iet/PAOL05hml9FymLHQdMHePL5GXs6hQQ98mjMLSds0gfeMw3sLhGOjNakuvmFopp11/YAZBgbw80a2wBF+yJ6Vj0ht+rODiykM+C6PlR0YnBeXp/p0srENq3eAlrhLNdAx/Mn3MwZ3h0lWUT3pnSf8LPqwyfp6D5h5nPBR/QZANaEuMsjU56CmtUFmJhSWB+VnyBRojCB6u83AW3PmI68r5c7ge9+Ct6Eb5fQhOzHiVpCgbrUS5OxYSv+P8zoYnjd71RRx86yhUq/RlIw6JklDGA4oitxPPntAMJm4llbCLtNQKBogtqedJJs8CwI6Fb0bw7qhsn9Y0OnhwgcQHVvU8EYZoNTzBcrQ2fZMm+X69cU6pDKQ0ij0znqJnILpDX01RmtkP0LXw2qyLLnkWYXFoOru37YIrELk/AaUQzc5LaSlsk9aRHA9AESOjyjw6joFBPqMu3b987FQJB1MM5XMjz+JNMSoVC+rNbcEPO1Jk4LXHBX3PoQRxTssGgLGIBXmvP/SoWfnzsegab4h93VIXFcG83O72H84WXhnUGrwfUhD1tW4B/n89HaSf1T/HvDQI6SjhJSfI60zkxP64RcVzPulYPsxZzBopFmkeq2fxO22x7tL8wpCAism6RObKM9PS36CqSWylq8S0PJPHvLWBqxgQ2tBVT87xeqh/Bw6W7bFrwveGPay41BekrqmoI4na97NWgkDyKHMKK/REqY/hcifL+uznE0E7nKTtJSMx5qWdCefraUuzfxL0QqHV/3sp1ouUdj+fOvZNpnm6eZbPaB2ka4d/0Fm8ZZVXUXmaTUx0z6TjvZiey5BMMD2Or0NaQ6J0SbVWfsKpBM9Kf1rBlCAv7jIvqKEjra++snmR tVCleSmv fr42CFwWMlpc1u9gqL3oHhELwf8+iF2qDy6Kq+EdOym0YxPZv0CZthAfOQAOCr7cguTivRn3Zr0uzGW/J3OPEIyvP4OAmaU6yWKmRdDlH2xCxNEbL3QogH8VeTzr/DgU++CT2PHnOxYaRelDO3SR5uysea1HotSiRexMmIobyBqD0KA8PpQM3CYNI1ZJO/wZzTfsARdg3O+y8dbrZSL/QxfjA92EuJENAyejCzxqDlG12lrof5iYwEAyNStiooexubNfc3+BPKoDfrjxvukvpHLqCrt3MoGEt2ueqaIaeI3wEiyqxIMkyRSKVoupzyCBIAlHJ1EImQ6G9L6FgpMAw0R8qOeMgLJl2G6Ax9mX1ISQGFGqYOXEU7yAxQEyZ8oNDOdVrCg4MztcOPOCd34IN/yOdCDy5IVbctxC4k059nV/A5Avgqcav6SuBcG8VxRKuqrHeNn2JVqp5OI8Of43l7YFCYQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: "Kiryl Shutsemau (Meta)" madvise_collapse() holds an mmgrab() reference across its work. It is redundant. Every caller already holds mm_users: - madvise(2) works on current->mm, which lives as long as the task is in the syscall; - process_madvise(2) reaches a remote mm through mm_access(), which takes an mm_users reference and holds it until the syscall returns; - io_uring passes current->mm; - DAMON takes one with get_task_mm() and drops it after the call. Drop the mmgrab()/mmdrop() pair. Assisted-by: Claude-Code:claude-opus-5 Signed-off-by: Kiryl Shutsemau (Meta) --- mm/khugepaged.c | 2 -- 1 file changed, 2 deletions(-) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index f49a6710933b..f1f8d4375e96 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -3236,7 +3236,6 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, cc->is_khugepaged = false; cc->progress = 0; - mmgrab(mm); lru_add_drain_all(); for (addr = hstart; addr < hend; addr += HPAGE_PMD_SIZE) { @@ -3292,7 +3291,6 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, } out_nolock: mmap_assert_locked(mm); - mmdrop(mm); kfree(cc); return thps == ((hend - hstart) >> HPAGE_PMD_SHIFT) ? 0 -- 2.54.0