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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 26 Jun 2025 03:53:05.2346 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 22259c31-bc01-4832-83b5-08ddb464f4cc X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[4.158.2.129];Helo=[outbound-uk1.az.dlp.m.darktrace.com] X-MS-Exchange-CrossTenant-AuthSource: AM2PEPF0001C708.eurprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DBBPR08MB6283 X-Rspamd-Queue-Id: 3A526120005 X-Rspam-User: X-Rspamd-Server: rspam06 X-Stat-Signature: oc5fbb7e8uypd4npxcz4oxmmtfp9u16d X-HE-Tag: 1750909991-147266 X-HE-Meta: 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 Uncg9rmY 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 25/06/25 6:58 pm, Lorenzo Stoakes wrote: > On Wed, Jun 25, 2025 at 11:28:06AM +0530, Dev Jain wrote: >> Suppose a folio is under migration, and khugepaged is also trying to >> collapse it. collapse_pte_mapped_thp() will retrieve the folio from the >> page cache via filemap_lock_folio(), thus taking a reference on the folio >> and sleeping on the folio lock, since the lock is held by the migration >> path. Migration will then fail in >> __folio_migrate_mapping -> folio_ref_freeze. Reduce the probability of >> such a race happening (leading to migration failure) by bailing out >> if we detect a PMD is marked with a migration entry. >> >> This fixes the migration-shared-anon-thp testcase failure on Apple M3. > Hm is this related to the series at all? Seems somewhat unrelated? Not related. > > Is there a Fixes, Closes, etc.? Do we need something in stable? We don't need anything. This is an "expected race" in the sense that both migration and khugepaged collapse are best effort algorithms. I am just seeing a test failure on my system because my system hits the race more often. So this patch reduces the window for the race. For some previous context, you may look at: https://lore.kernel.org/all/20240801081657.1386743-1-dev.jain@arm.com/ and https://lore.kernel.org/all/20240830051609.4037834-1-dev.jain@arm.com/ > >> Signed-off-by: Dev Jain >> --- >> mm/khugepaged.c | 12 ++++++++++-- >> 1 file changed, 10 insertions(+), 2 deletions(-) >> >> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >> index 4c8d33abfbd8..bc8774f62e86 100644 >> --- a/mm/khugepaged.c >> +++ b/mm/khugepaged.c >> @@ -31,6 +31,7 @@ enum scan_result { >> SCAN_FAIL, >> SCAN_SUCCEED, >> SCAN_PMD_NULL, >> + SCAN_PMD_MIGRATION, >> SCAN_PMD_NONE, >> SCAN_PMD_MAPPED, >> SCAN_EXCEED_NONE_PTE, >> @@ -956,6 +957,8 @@ static inline int check_pmd_state(pmd_t *pmd) >> >> if (pmd_none(pmde)) >> return SCAN_PMD_NONE; >> + if (is_pmd_migration_entry(pmde)) >> + return SCAN_PMD_MIGRATION; >> if (!pmd_present(pmde)) >> return SCAN_PMD_NULL; >> if (pmd_trans_huge(pmde)) >> @@ -1518,9 +1521,12 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr, >> !range_in_vma(vma, haddr, haddr + HPAGE_PMD_SIZE)) >> return SCAN_VMA_CHECK; >> >> - /* Fast check before locking page if already PMD-mapped */ >> + /* >> + * Fast check before locking folio if already PMD-mapped, or if the >> + * folio is under migration >> + */ >> result = find_pmd_or_thp_or_none(mm, haddr, &pmd); >> - if (result == SCAN_PMD_MAPPED) >> + if (result == SCAN_PMD_MAPPED || result == SCAN_PMD_MIGRATION) >> return result; >> >> /* >> @@ -2745,6 +2751,7 @@ static int madvise_collapse_errno(enum scan_result r) >> case SCAN_PAGE_LRU: >> case SCAN_DEL_PAGE_LRU: >> case SCAN_PAGE_FILLED: >> + case SCAN_PMD_MIGRATION: >> return -EAGAIN; >> /* >> * Other: Trying again likely not to succeed / error intrinsic to >> @@ -2834,6 +2841,7 @@ int madvise_collapse(struct vm_area_struct *vma, struct vm_area_struct **prev, >> goto handle_result; >> /* Whitelisted set of results where continuing OK */ >> case SCAN_PMD_NULL: >> + case SCAN_PMD_MIGRATION: >> case SCAN_PTE_NON_PRESENT: >> case SCAN_PTE_UFFD_WP: >> case SCAN_PAGE_RO: >> -- >> 2.30.2 >>