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This is misleading as EINVAL suggests invalid arguments, whereas dirty/writeback pages represent transient conditions that may resolve on retry. Introduce SCAN_PAGE_DIRTY_OR_WRITEBACK to cover both dirty and writeback states, mapping it to -EAGAIN. For MADV_COLLAPSE, this provides userspace with a clear signal that retry may succeed after writeback completes. For khugepaged, this is harmless as it will naturally revisit the range during periodic scans after async writeback completes. Reported-by: Branden Moore Closes: https://lore.kernel.org/all/4e26fe5e-7374-467c-a333-9dd48f85d7cc@am= d.com Fixes: 34488399fa08 ("mm/madvise: add file and shmem support to MADV_COLLAP= SE") Reviewed-by: Dev Jain Reviewed-by: Lance Yang Signed-off-by: Shivank Garg --- include/trace/events/huge_memory.h | 3 ++- mm/khugepaged.c | 8 +++++--- 2 files changed, 7 insertions(+), 4 deletions(-) diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge= _memory.h index 4cde53b45a85..4e41bff31888 100644 --- a/include/trace/events/huge_memory.h +++ b/include/trace/events/huge_memory.h @@ -37,7 +37,8 @@ EM( SCAN_PAGE_HAS_PRIVATE, "page_has_private") \ EM( SCAN_STORE_FAILED, "store_failed") \ EM( SCAN_COPY_MC, "copy_poisoned_page") \ - EMe(SCAN_PAGE_FILLED, "page_filled") + EM( SCAN_PAGE_FILLED, "page_filled") \ + EMe(SCAN_PAGE_DIRTY_OR_WRITEBACK, "page_dirty_or_writeback") =20 #undef EM #undef EMe diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 97d1b2824386..219dfa2e523c 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -58,6 +58,7 @@ enum scan_result { SCAN_STORE_FAILED, SCAN_COPY_MC, SCAN_PAGE_FILLED, + SCAN_PAGE_DIRTY_OR_WRITEBACK, }; =20 #define CREATE_TRACE_POINTS @@ -1967,11 +1968,11 @@ static int collapse_file(struct mm_struct *mm, unsi= gned long addr, */ xas_unlock_irq(&xas); filemap_flush(mapping); - result =3D SCAN_FAIL; + result =3D SCAN_PAGE_DIRTY_OR_WRITEBACK; goto xa_unlocked; } else if (folio_test_writeback(folio)) { xas_unlock_irq(&xas); - result =3D SCAN_FAIL; + result =3D SCAN_PAGE_DIRTY_OR_WRITEBACK; goto xa_unlocked; } else if (folio_trylock(folio)) { folio_get(folio); @@ -2018,7 +2019,7 @@ static int collapse_file(struct mm_struct *mm, unsign= ed long addr, * folio is dirty because it hasn't been flushed * since first write. */ - result =3D SCAN_FAIL; + result =3D SCAN_PAGE_DIRTY_OR_WRITEBACK; goto out_unlock; } =20 @@ -2747,6 +2748,7 @@ static int madvise_collapse_errno(enum scan_result r) case SCAN_PAGE_LRU: case SCAN_DEL_PAGE_LRU: case SCAN_PAGE_FILLED: + case SCAN_PAGE_DIRTY_OR_WRITEBACK: return -EAGAIN; /* * Other: Trying again likely not to succeed / error intrinsic to --=20 2.43.0 From nobody Mon Dec 1 20:57:16 2025 Received: from PH7PR06CU001.outbound.protection.outlook.com (mail-westus3azon11010052.outbound.protection.outlook.com [52.101.201.52]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4774D227B94; 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Mon, 1 Dec 2025 13:03:18 -0600 From: Shivank Garg To: Andrew Morton , David Hildenbrand , Lorenzo Stoakes CC: Zi Yan , Baolin Wang , "Liam R . Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Steven Rostedt , Masami Hiramatsu , "Mathieu Desnoyers" , Zach O'Keefe , , , , , Branden Moore Subject: [PATCH V3 2/2] mm/khugepaged: retry with sync writeback for MADV_COLLAPSE Date: Mon, 1 Dec 2025 18:56:11 +0000 Message-ID: <20251201185604.210634-10-shivankg@amd.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20251201185604.210634-6-shivankg@amd.com> References: <20251201185604.210634-6-shivankg@amd.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 X-ClientProxiedBy: satlexmb08.amd.com (10.181.42.217) To satlexmb07.amd.com (10.181.42.216) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS2PEPF0000343F:EE_|BN7PPFD3499E3E3:EE_ X-MS-Office365-Filtering-Correlation-Id: d0b8dfb9-0545-4ebc-8463-08de310c4f10 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|82310400026|36860700013|376014|1800799024; X-Microsoft-Antispam-Message-Info: =?us-ascii?Q?nNYnCBrvYsYY9nPUA8wieq0EwAFQCjGpUQKMaWVlxDUl3yilNhLMI2d1XVEA?= =?us-ascii?Q?Yj/TG43x2PgZ0iYwHrdy7G4+oACCDWe0cCVFsA8r00lnF9HZkqJJ7zs6VbIl?= =?us-ascii?Q?Q9NOHiIlHDSz8zTUckZlcenskMx0taICGmnYmzTalN3HZFiT8aWNpuIDDocR?= =?us-ascii?Q?vU+cuJvaXzUbyz3ZTQqaPh7ChSMnnG3DDLeq3JVztL34tP0uSj/Y6Ig8OyO7?= =?us-ascii?Q?kCMVnCTZIqudnUJMwWxNY2ttnXGhUjb/LAcoPHJOqOoKPaDi9fXLd53M2xKv?= =?us-ascii?Q?A0EJ8gPt43iY2oxFrKPhaJVBOC7pMZNNhJflqcM8gyIXMIRH7gDdrB2ZFrvg?= =?us-ascii?Q?F5F30QRnsw8xJv3YOyx0D2hIEjie+c3hP8mPjs73sHFb7HC7AqZjMdLg/ajl?= =?us-ascii?Q?FYiUGE1qNo07GztSWbP7juG3X8fjoh0tjvJ17aTxVqKDIJ7lkFsFjip4q9zp?= =?us-ascii?Q?e4qOXIYnbsVPPR86ETqQ/nk7APCKZF0qw/XjDL0Uf6H+kXQFf6jWLUvSDZt9?= =?us-ascii?Q?/NRtHunYESo8O+4403YroMBIjV8FSb+y5hOBxVuRkiuDLjsW/6DzeyymdDqS?= =?us-ascii?Q?URdjl7LCielm7pMCNEQrLj3SBmzj+OogbuFTJjfaiNe6ZRCsq1ldbam5rsfj?= =?us-ascii?Q?PC94xnUTMYgmteLSn5899VNl3pV24Cq8jubXjU7MrNOpoH5XM41LYujsAyxm?= =?us-ascii?Q?Z0238o1tUUjCRXlXO2RA7m6sjhFKsZuSzI562lqArZtlSk9GyZVYwbjEDC4j?= =?us-ascii?Q?3lVJ3r8H8rbJDFGjSGqVixL1JGAGBqFsHpHfkAUm5SywlvKDQVcwjExxFPII?= =?us-ascii?Q?J2xOUx3gQZUrT6MJ/po/Al3fbjoQwsuiLIPFHfOSkNMO/mPz7BKI1t7qCsyQ?= =?us-ascii?Q?bz6x0XYBPoZ6RABAdmzTUsrUB/7E72R7TUWzoUtQKmadfQ/r+GEuP2NcSh/3?= =?us-ascii?Q?f6Ln2kwbWTw5XJNYTWJKJthx2IbspA+j2yezgaev+U8qqiC/mBZVUCUYfRgD?= =?us-ascii?Q?DYc/beukW5MhG7xqVFmYfJeL8j4gEG4tT5Xok7vjqYrlsnwUtircZbWgBV4d?= =?us-ascii?Q?/8Zn89pQpWIGmZiEyff1BLEpD8hipBx+lxN/GqSxu+oAmyK0IoIQ5WZrUKoh?= =?us-ascii?Q?i3a/gxbB6N1ms/PQOHI0TNO/Vdw9aT7qXmU3hrXNvkusZXcdM2E3KDGJ3J6W?= =?us-ascii?Q?bVPew1LBvrXz0+nm+APQDp929a9Ot8/KuuFuGcNai/IHDMJiMw39aHvlN16g?= =?us-ascii?Q?qhUvYEn+yZUWxSoPdUJvDpv+L3d56KK1/k2RjJFQMkD2huJAmGxbNaR24Z0+?= =?us-ascii?Q?NBuLZ+HiwZeee9iZ1pa7ycgqOtJKXhCCSSvpMLrncGzmu6WQEShSEK+PK424?= =?us-ascii?Q?sOOJEsoG4ZHDt4MtoSkxbyVlTnODqMFAU1ahQcxY9n7zo6hkqflXKW8vVLIQ?= =?us-ascii?Q?ENwjsP2Cpofu64A6FVANhHku0zBpAYZ3Ft9719rahnJqAbX7fW1KYKh7E8qY?= =?us-ascii?Q?bVlxkpN+0Lb3DwfWiPzaUjNfqOQ9P/4MFqqM?= X-Forefront-Antispam-Report: CIP:165.204.84.17;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:satlexmb07.amd.com;PTR:InfoDomainNonexistent;CAT:NONE;SFS:(13230040)(7416014)(82310400026)(36860700013)(376014)(1800799024);DIR:OUT;SFP:1101; X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 01 Dec 2025 19:03:26.8180 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: d0b8dfb9-0545-4ebc-8463-08de310c4f10 X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[satlexmb07.amd.com] X-MS-Exchange-CrossTenant-AuthSource: DS2PEPF0000343F.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN7PPFD3499E3E3 Content-Type: text/plain; charset="utf-8" When MADV_COLLAPSE is called on file-backed mappings (e.g., executable text sections), the pages may still be dirty from recent writes. collapse_file() will trigger async writeback and fail with SCAN_PAGE_DIRTY_OR_WRITEBACK (-EAGAIN). MADV_COLLAPSE is a synchronous operation where userspace expects immediate results. If the collapse fails due to dirty pages, perform synchronous writeback on the specific range and retry once. This avoids spurious failures for freshly written executables while avoiding unnecessary synchronous I/O for mappings that are already clean. Reported-by: Branden Moore Closes: https://lore.kernel.org/all/4e26fe5e-7374-467c-a333-9dd48f85d7cc@am= d.com Fixes: 34488399fa08 ("mm/madvise: add file and shmem support to MADV_COLLAP= SE") Suggested-by: David Hildenbrand Signed-off-by: Shivank Garg --- mm/khugepaged.c | 41 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 41 insertions(+) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 219dfa2e523c..7a12e9ef30b4 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -22,6 +22,7 @@ #include #include #include +#include =20 #include #include "internal.h" @@ -2787,9 +2788,11 @@ int madvise_collapse(struct vm_area_struct *vma, uns= igned long start, hend =3D end & HPAGE_PMD_MASK; =20 for (addr =3D hstart; addr < hend; addr +=3D HPAGE_PMD_SIZE) { + bool retried =3D false; int result =3D SCAN_FAIL; =20 if (!mmap_locked) { +retry: cond_resched(); mmap_read_lock(mm); mmap_locked =3D true; @@ -2819,6 +2822,44 @@ int madvise_collapse(struct vm_area_struct *vma, uns= igned long start, if (!mmap_locked) *lock_dropped =3D true; =20 + /* + * If the file-backed VMA has dirty pages, the scan triggers + * async writeback and returns SCAN_PAGE_DIRTY_OR_WRITEBACK. + * Since MADV_COLLAPSE is sync, we force sync writeback and + * retry once. + */ + if (result =3D=3D SCAN_PAGE_DIRTY_OR_WRITEBACK && !retried) { + /* + * File scan drops the lock. We must re-acquire it to + * safely inspect the VMA and hold the file reference. + */ + if (!mmap_locked) { + cond_resched(); + mmap_read_lock(mm); + mmap_locked =3D true; + result =3D hugepage_vma_revalidate(mm, addr, false, &vma, cc); + if (result !=3D SCAN_SUCCEED) + goto handle_result; + } + + if (!vma_is_anonymous(vma) && vma->vm_file && + mapping_can_writeback(vma->vm_file->f_mapping)) { + struct file *file =3D get_file(vma->vm_file); + pgoff_t pgoff =3D linear_page_index(vma, addr); + loff_t lstart =3D (loff_t)pgoff << PAGE_SHIFT; + loff_t lend =3D lstart + HPAGE_PMD_SIZE - 1; + + mmap_read_unlock(mm); + mmap_locked =3D false; + *lock_dropped =3D true; + filemap_write_and_wait_range(file->f_mapping, lstart, lend); + fput(file); + retried =3D true; + goto retry; + } + } + + handle_result: switch (result) { case SCAN_SUCCEED: --=20 2.43.0