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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 03 Sep 2025 09:16:08.5739 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: c05b48f0-592c-47f0-6ae4-08ddeaca84ad 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: DB1PEPF000509EE.eurprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: AM7PR08MB5494 X-Rspamd-Queue-Id: DAA1020008 X-Stat-Signature: fgo3q78764ftp1yn6rsndmywwt34t7h8 X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1756890972-375720 X-HE-Meta: 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 DRiZFJ2P 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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 03/09/25 1:38 pm, Wei Yang wrote: > On Wed, Sep 03, 2025 at 11:16:34AM +0530, Dev Jain wrote: >> Currently khugepaged does not collapse a region which does not have a >> single writable page. This is wasteful since non-writable VMAs mapped by >> the application won't benefit from THP collapse. Therefore, remove this >> restriction and allow khugepaged to collapse a VMA with arbitrary >> protections. >> >> Along with this, currently MADV_COLLAPSE does not perform a collapse on a >> non-writable VMA, and this restriction is nowhere to be found on the >> manpage - the restriction itself sounds wrong to me since the user knows >> the protection of the memory it has mapped, so collapsing read-only >> memory via madvise() should be a choice of the user which shouldn't >> be overriden by the kernel. >> >> On an arm64 machine, an average of 5% improvement is seen on some mmtests >> benchmarks, particularly hackbench, with a maximum improvement of 12%. >> >> Signed-off-by: Dev Jain >> --- > [...] >> mm/khugepaged.c | 9 ++------- >> 1 file changed, 2 insertions(+), 7 deletions(-) >> >> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >> index 4ec324a4c1fe..a0f1df2a7ae6 100644 >> --- a/mm/khugepaged.c >> +++ b/mm/khugepaged.c >> @@ -676,9 +676,7 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma, >> writable = true; >> } >> >> - if (unlikely(!writable)) { >> - result = SCAN_PAGE_RO; >> - } else if (unlikely(cc->is_khugepaged && !referenced)) { > Would this cause more memory usage in system? > > For example, one application would fork itself many times. It executable area > is read only, so all of them share one copy in memory. > > Now we may collapse the range and create one copy for each process. > > Ok, we have max_ptes_shared, while if some ptes are none, could it still do > collapse? > > Maybe this is not realistic, just curious. Misunderstood your concern - you mean to say that a parent forks and the children VMAs are read-only pointing to the pages which were mapped by parent. Hmm. > >> + if (unlikely(cc->is_khugepaged && !referenced)) { >> result = SCAN_LACK_REFERENCED_PAGE; >> } else { >> result = SCAN_SUCCEED; >> @@ -1421,9 +1419,7 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm, >> mmu_notifier_test_young(vma->vm_mm, _address))) >> referenced++; >> } >> - if (!writable) { >> - result = SCAN_PAGE_RO; >> - } else if (cc->is_khugepaged && >> + if (cc->is_khugepaged && >> (!referenced || >> (unmapped && referenced < HPAGE_PMD_NR / 2))) { >> result = SCAN_LACK_REFERENCED_PAGE; >> @@ -2830,7 +2826,6 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, >> case SCAN_PMD_NULL: >> case SCAN_PTE_NON_PRESENT: >> case SCAN_PTE_UFFD_WP: >> - case SCAN_PAGE_RO: >> case SCAN_LACK_REFERENCED_PAGE: >> case SCAN_PAGE_NULL: >> case SCAN_PAGE_COUNT: >> -- >> 2.30.2 >>