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Sun, 11 Jan 2026 04:19:50 -0800 (PST) From: Vernon Yang X-Google-Original-From: Vernon Yang To: akpm@linux-foundation.org, david@kernel.org Cc: lorenzo.stoakes@oracle.com, ziy@nvidia.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Vernon Yang Subject: [PATCH mm-new v4 3/6] mm: khugepaged: just skip when the memory has been collapsed Date: Sun, 11 Jan 2026 20:19:06 +0800 Message-ID: <20260111121909.8410-4-yanglincheng@kylinos.cn> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260111121909.8410-1-yanglincheng@kylinos.cn> References: <20260111121909.8410-1-yanglincheng@kylinos.cn> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 45E80180002 X-Stat-Signature: iqr5eyy3t3nue9xiop41u78t1pq1httg X-Rspam-User: X-HE-Tag: 1768133992-342601 X-HE-Meta: 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 a+VPXQOF heMThe+Iu62cl/rFvpp2IFGm0bsYw67ZZganzNJz1o5USoijq/xPETAEnwbZmd/H4jWOXq15fFVkML4Qjmq2bAsPJdwZCkLEqjxNWHS4xJAShp6Off+UMlm4C1FVlgac+JUFa/fqjcnsTN8NQ/10/LBMhbpsDeRS4ii0e5OkK5cXkluxA5ZsArYHoZkuZJ80WHbY4pwkAYitrTFA6Kt05JGSheCpAAZ5ldF5oewAI/EPBEu1VioAijWIWQm8EKpPe4weHovfdWHcCWVyeakM/DZGxeQh/0A2h2mRNuMyQCwlTU7dLz+sjV+nceQ/F7POtNHBLZ+pCAsM6SkRmW19pgKF7t3gGSvDWD2Zzs0sFxzWdvhj3bHXA2D+CY9S4RAhh3Cfy 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: The following data is traced by bpftrace on a desktop system. After the system has been left idle for 10 minutes upon booting, a lot of SCAN_PMD_MAPPED or SCAN_NO_PTE_TABLE are observed during a full scan by khugepaged. @scan_pmd_status[1]: 1 ## SCAN_SUCCEED @scan_pmd_status[6]: 2 ## SCAN_EXCEED_SHARED_PTE @scan_pmd_status[3]: 142 ## SCAN_PMD_MAPPED @scan_pmd_status[2]: 178 ## SCAN_NO_PTE_TABLE total progress size: 674 MB Total time : 419 seconds ## include khugepaged_scan_sleep_millisecs The khugepaged_scan list save all task that support collapse into hugepage, as long as the task is not destroyed, khugepaged will not remove it from the khugepaged_scan list. This exist a phenomenon where task has already collapsed all memory regions into hugepage, but khugepaged continues to scan it, which wastes CPU time and invalid, and due to khugepaged_scan_sleep_millisecs (default 10s) causes a long wait for scanning a large number of invalid task, so scanning really valid task is later. After applying this patch, when the memory is either SCAN_PMD_MAPPED or SCAN_NO_PTE_TABLE, just skip it, as follow: @scan_pmd_status[6]: 2 @scan_pmd_status[3]: 147 @scan_pmd_status[2]: 173 total progress size: 45 MB Total time : 20 seconds Signed-off-by: Vernon Yang --- mm/khugepaged.c | 17 +++++++++++------ 1 file changed, 11 insertions(+), 6 deletions(-) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 5c6015ac7b5e..6df2857d94c6 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -68,7 +68,10 @@ enum scan_result { static struct task_struct *khugepaged_thread __read_mostly; static DEFINE_MUTEX(khugepaged_mutex); -/* default scan 8*HPAGE_PMD_NR ptes (or vmas) every 10 second */ +/* + * default scan 8*HPAGE_PMD_NR ptes, pmd_mapped, no_pte_table or vmas + * every 10 second. + */ static unsigned int khugepaged_pages_to_scan __read_mostly; static unsigned int khugepaged_pages_collapsed; static unsigned int khugepaged_full_scans; @@ -1267,7 +1270,7 @@ static enum scan_result hpage_collapse_scan_pmd(struct mm_struct *mm, result = find_pmd_or_thp_or_none(mm, start_addr, &pmd); if (result != SCAN_SUCCEED) { if (cur_progress) - *cur_progress = HPAGE_PMD_NR; + *cur_progress = 1; goto out; } @@ -1276,7 +1279,7 @@ static enum scan_result hpage_collapse_scan_pmd(struct mm_struct *mm, pte = pte_offset_map_lock(mm, pmd, start_addr, &ptl); if (!pte) { if (cur_progress) - *cur_progress = HPAGE_PMD_NR; + *cur_progress = 1; result = SCAN_NO_PTE_TABLE; goto out; } @@ -2347,9 +2350,6 @@ static enum scan_result hpage_collapse_scan_file(struct mm_struct *mm, unsigned continue; } - if (cur_progress) - *cur_progress += folio_nr_pages(folio); - if (folio_order(folio) == HPAGE_PMD_ORDER && folio->index == start) { /* Maybe PMD-mapped */ @@ -2361,9 +2361,14 @@ static enum scan_result hpage_collapse_scan_file(struct mm_struct *mm, unsigned * returning. */ folio_put(folio); + if (cur_progress) + *cur_progress += 1; break; } + if (cur_progress) + *cur_progress += folio_nr_pages(folio); + node = folio_nid(folio); if (hpage_collapse_scan_abort(node, cc)) { result = SCAN_SCAN_ABORT; -- 2.51.0