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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 01 Sep 2025 08:40:04.3513 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: e297f122-8208-4ec8-2960-08dde93325e1 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: DU6PEPF00009527.eurprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: AS4PR08MB7949 X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 1808920007 X-Stat-Signature: pisgf4csiraaomweeajbgzhkuhsy5ewt X-Rspam-User: X-HE-Tag: 1756716010-579723 X-HE-Meta: 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 s+xb1N9O 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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 01/09/25 1:53 pm, Kiryl Shutsemau wrote: > On Mon, Sep 01, 2025 at 01:18:17PM +0530, Dev Jain wrote: >> Currently khugepaged does not collapse a region which does not have a >> single writable page. This is wasteful since, apart from any non-writable >> memory mapped by the application, there are a lot of non-writable VMAs >> which will benefit from collapsing - the VMAs of the executable, those >> of the glibc, vvar and vdso, which won't be unmapped during the lifetime >> of the process, as opposed to other VMAs which maybe unmapped. 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. >> >> I dug into the history of this and couldn't find any concrete reason of >> the current behaviour - [1] is the v1 of the original khugepaged patch >> which required all ptes to be writable. [2] is the v1 of the patch which >> changed this behaviour to require at least one pte to be writable. The >> closest thing I could find was: in response to [2], Kirill says in [3] - >> "As a side effect it will effectively allow collapse in PROT_READ vmas, >> right? I'm not convinced it's a good idea." (Although Kirill realizes in >> [4] that this was not the intention of the patch). > Hm. I don't see a justification for only collapsing writable pages. Glad we are on the same page :) > >> I can see performance improvements on mmtests run on an arm64 machine >> comparing with 6.17-rc2. (I) denotes statistically significant improvement, >> (R) denotes statistically significant regression (Please ignore the >> numbers in the middle column): > Could you give a summary instead of raw data? It is too much for commit > message. Raw data can be put under "---" for reference. Okay. > > BTW, why did you pick hackbench as a benchmark? Seems random. I didn't actually run mmtests myself (in fact I have consistently failed to run mmtests - someday I'll gather the courage to figure it out again :)) - I just start a test pipeline which runs tests for me and gets me results. The pipeline ran sysbench-cpu, sysbench-mutex, sysbench-thread, kernbench and hackbench for me. For the others not mentioned in the below table, I didn't get any statistically significant results. > >> +------------------------------------+----------------------------------------------------------+-----------------------+--------------------------+ >> | mmtests/hackbench | process-pipes-1 (seconds) | 0.145 | -0.06% | >> | | process-pipes-4 (seconds) | 0.4335 | -0.27% | >> | | process-pipes-7 (seconds) | 0.823 | (I) -12.13% | >> | | process-pipes-12 (seconds) | 1.3538333333333334 | (I) -5.32% | >> | | process-pipes-21 (seconds) | 1.8971666666666664 | (I) -2.87% | >> | | process-pipes-30 (seconds) | 2.5023333333333335 | (I) -3.39% | >> | | process-pipes-48 (seconds) | 3.4305 | (I) -5.65% | >> | | process-pipes-79 (seconds) | 4.245833333333334 | (I) -6.74% | >> | | process-pipes-110 (seconds) | 5.114833333333333 | (I) -6.26% | >> | | process-pipes-141 (seconds) | 6.1885 | (I) -4.99% | >> | | process-pipes-172 (seconds) | 7.231833333333334 | (I) -4.45% | >> | | process-pipes-203 (seconds) | 8.393166666666668 | (I) -3.65% | >> | | process-pipes-234 (seconds) | 9.487499999999999 | (I) -3.45% | >> | | process-pipes-256 (seconds) | 10.316166666666666 | (I) -3.47% | >> | | process-sockets-1 (seconds) | 0.289 | 2.13% | >> | | process-sockets-4 (seconds) | 0.7596666666666666 | 1.02% | >> | | process-sockets-7 (seconds) | 1.1663333333333334 | -0.26% | >> | | process-sockets-12 (seconds) | 1.8641666666666665 | -1.24% | >> | | process-sockets-21 (seconds) | 3.0773333333333333 | 0.01% | >> | | process-sockets-30 (seconds) | 4.2405 | -0.15% | >> | | process-sockets-48 (seconds) | 6.459666666666666 | 0.15% | >> | | process-sockets-79 (seconds) | 10.156833333333333 | 1.45% | >> | | process-sockets-110 (seconds) | 14.317833333333333 | -1.64% | >> | | process-sockets-141 (seconds) | 20.8735 | (I) -4.27% | >> | | process-sockets-172 (seconds) | 26.205333333333332 | 0.30% | >> | | process-sockets-203 (seconds) | 31.298000000000002 | -1.71% | >> | | process-sockets-234 (seconds) | 36.104000000000006 | -1.94% | >> | | process-sockets-256 (seconds) | 39.44016666666667 | -0.71% | >> | | thread-pipes-1 (seconds) | 0.17550000000000002 | 0.66% | >> | | thread-pipes-4 (seconds) | 0.44716666666666666 | 1.66% | >> | | thread-pipes-7 (seconds) | 0.7345 | -0.17% | >> | | thread-pipes-12 (seconds) | 1.405833333333333 | (I) -4.12% | >> | | thread-pipes-21 (seconds) | 2.0113333333333334 | (I) -2.13% | >> | | thread-pipes-30 (seconds) | 2.6648333333333336 | (I) -3.78% | >> | | thread-pipes-48 (seconds) | 3.6341666666666668 | (I) -5.77% | >> | | thread-pipes-79 (seconds) | 4.4085 | (I) -5.31% | >> | | thread-pipes-110 (seconds) | 5.374666666666666 | (I) -6.12% | >> | | thread-pipes-141 (seconds) | 6.385666666666666 | (I) -4.00% | >> | | thread-pipes-172 (seconds) | 7.403000000000001 | (I) -3.01% | >> | | thread-pipes-203 (seconds) | 8.570333333333332 | (I) -2.62% | >> | | thread-pipes-234 (seconds) | 9.719166666666666 | (I) -2.00% | >> | | thread-pipes-256 (seconds) | 10.552833333333334 | (I) -2.30% | >> | | thread-sockets-1 (seconds) | 0.3065 | (R) 2.39% | >> +------------------------------------+----------------------------------------------------------+-----------------------+--------------------------+ >> >> +------------------------------------+----------------------------------------------------------+-----------------------+--------------------------+ >> | mmtests/sysbench-mutex | sysbenchmutex-1 (usec) | 194.38333333333333 | -0.02% | >> | | sysbenchmutex-4 (usec) | 200.875 | -0.02% | >> | | sysbenchmutex-7 (usec) | 201.23000000000002 | 0.00% | >> | | sysbenchmutex-12 (usec) | 201.77666666666664 | 0.12% | >> | | sysbenchmutex-21 (usec) | 203.03 | -0.40% | >> | | sysbenchmutex-30 (usec) | 203.285 | 0.08% | >> | | sysbenchmutex-48 (usec) | 231.30000000000004 | 2.59% | >> | | sysbenchmutex-79 (usec) | 362.075 | -0.80% | >> | | sysbenchmutex-110 (usec) | 516.8233333333334 | -3.87% | >> | | sysbenchmutex-128 (usec) | 593.3533333333334 | (I) -4.46% | >> +------------------------------------+----------------------------------------------------------+-----------------------+--------------------------+ >> >> No regressions were observed with mm-selftests. >> >> [1] https://lore.kernel.org/all/679861e2e81b32a0ae08.1264054854@v2.random/ >> [2] https://lore.kernel.org/all/1421999256-3881-1-git-send-email-ebru.akagunduz@gmail.com/ >> [3] https://lore.kernel.org/all/20150123113701.GB5975@node.dhcp.inet.fi/ >> [4] https://lore.kernel.org/all/20150123155802.GA7011@node.dhcp.inet.fi/ >> >> Signed-off-by: Dev Jain >> --- >> Based on mm-new. >> >> Not very sure of the tracing parts which this patch changes. I have kept >> the writable portion for the tracing to maintain backward compat, just >> dropped it as a collapse condition. >> >> include/trace/events/huge_memory.h | 2 +- >> mm/khugepaged.c | 11 +++-------- >> 2 files changed, 4 insertions(+), 9 deletions(-) >> >> diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h >> index 2305df6cb485..f2472c1c132a 100644 >> --- a/include/trace/events/huge_memory.h >> +++ b/include/trace/events/huge_memory.h >> @@ -19,7 +19,7 @@ >> EM( SCAN_PTE_NON_PRESENT, "pte_non_present") \ >> EM( SCAN_PTE_UFFD_WP, "pte_uffd_wp") \ >> EM( SCAN_PTE_MAPPED_HUGEPAGE, "pte_mapped_hugepage") \ >> - EM( SCAN_PAGE_RO, "no_writable_page") \ >> + EM( SCAN_PAGE_RO, "no_writable_page") /* deprecated */ \ > Why not remove SCAN_PAGE_RO? I was wondering whether any userspace script could fail due to using this metric already? > >> EM( SCAN_LACK_REFERENCED_PAGE, "lack_referenced_page") \ >> EM( SCAN_PAGE_NULL, "page_null") \ >> EM( SCAN_SCAN_ABORT, "scan_aborted") \ >> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >> index 4ec324a4c1fe..5ef8482597a9 100644 >> --- a/mm/khugepaged.c >> +++ b/mm/khugepaged.c >> @@ -39,7 +39,7 @@ enum scan_result { >> SCAN_PTE_NON_PRESENT, >> SCAN_PTE_UFFD_WP, >> SCAN_PTE_MAPPED_HUGEPAGE, >> - SCAN_PAGE_RO, >> + SCAN_PAGE_RO, /* deprecated */ >> SCAN_LACK_REFERENCED_PAGE, >> SCAN_PAGE_NULL, >> SCAN_SCAN_ABORT, >> @@ -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)) { >> + 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 && > The only practical use of the writable is gone. The only other usage is > tracing which can be dropped to as it is not actionable anymore. > > Could you drop writable? Maybe as a separate commit. > >> (!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 >>