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Sat, 03 Jan 2026 21:41:54 -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, richard.weiyang@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Vernon Yang Subject: [PATCH v3 3/6] mm: khugepaged: just skip when the memory has been collapsed Date: Sun, 4 Jan 2026 13:41:09 +0800 Message-ID: <20260104054112.4541-4-yanglincheng@kylinos.cn> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260104054112.4541-1-yanglincheng@kylinos.cn> References: <20260104054112.4541-1-yanglincheng@kylinos.cn> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Queue-Id: 3E4B220002 X-Rspamd-Server: rspam10 X-Stat-Signature: cdkmj1i73ikozjn4fos99zgwrz4wxzur X-HE-Tag: 1767505316-237058 X-HE-Meta: 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 3bImAwdB 8CYwctOihL1YtpGwGM7lfRGyRh5MaOsY9UCnX6R9MoMPL5ROPDKNeI0ueqbBggsGZ2rxsNuxRKtqCTJnpDYUHZcHQEYvf/qNmwiomL0jjmmHtyCKUMwmPQyl36hPUGJD8Ks+DaSzeBduAGIr2SxbwA0WYi9LkiN1EhzH0koFk4f0CyyuPusm/2jdRPPFOMRYPMgw4Qdxh4PU4dC6rCIrPF5Wye5XioSm5890VUg0POoYYHX6yXqTs9Us/ZSK/XG8XtyCeWDupiJXRmo0LuhNIzaJU6TWR07P7h0IQ3AcfL3WFxVsY+ReRnitXLX617i9fI5r5N2zV/hbnLxNmxpMmcfGWE96Ydz8gZQ0Y+qHl93AfNcIAP92KVybCAGVoxKNxBfpV3jqHH7IVp8fRjuZFI7I8gDl299c1AeEsC0jQ8o2eWq7ZA5dvvLDfOWUWrm+mEE7iHsw5nSAD7IA= 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 | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 4b124e854e2e..30786c706c4a 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -66,7 +66,10 @@ 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; @@ -1264,7 +1267,7 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm, result = find_pmd_or_thp_or_none(mm, start_addr, &pmd); if (result != SCAN_SUCCEED) { - _progress = HPAGE_PMD_NR; + _progress = 1; goto out; } @@ -1272,7 +1275,7 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm, nodes_clear(cc->alloc_nmask); pte = pte_offset_map_lock(mm, pmd, start_addr, &ptl); if (!pte) { - _progress = HPAGE_PMD_NR; + _progress = 1; result = SCAN_NO_PTE_TABLE; goto out; } @@ -2336,8 +2339,6 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr, continue; } - _progress += folio_nr_pages(folio); - if (folio_order(folio) == HPAGE_PMD_ORDER && folio->index == start) { /* Maybe PMD-mapped */ @@ -2349,9 +2350,12 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr, * returning. */ folio_put(folio); + _progress++; break; } + _progress += folio_nr_pages(folio); + node = folio_nid(folio); if (hpage_collapse_scan_abort(node, cc)) { result = SCAN_SCAN_ABORT; -- 2.51.0