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imf23.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf23.hostedemail.com: domain of dev.jain@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=dev.jain@arm.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1770542246; a=rsa-sha256; cv=none; b=t9IE3eN1LzF+4FlXthudt7+AwzRTU0qkjpTxfTjYgxQd2AbPC5IGURpFquo7sXxppxz+4X DR5OSheQ6KV2XB1pG2rfzP/SdFWyd4d9mVRVJ3Dv2UAEHW32t3dMy1oK0NrcqML9a7mX86 QToOXXry8NewI5ezU1IM6n+7dpiSiWg= Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 83694339; Sun, 8 Feb 2026 01:17:18 -0800 (PST) Received: from [10.164.10.250] (unknown [10.164.10.250]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id D86AC3F740; Sun, 8 Feb 2026 01:17:21 -0800 (PST) Message-ID: <53527839-e918-47d3-9442-cd5e8975ab22@arm.com> Date: Sun, 8 Feb 2026 14:47:18 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH mm-new v7 2/5] mm: khugepaged: refine scan progress number To: Vernon Yang , akpm@linux-foundation.org, david@kernel.org Cc: lorenzo.stoakes@oracle.com, ziy@nvidia.com, baohua@kernel.org, lance.yang@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Vernon Yang References: <20260207081613.588598-1-vernon2gm@gmail.com> <20260207081613.588598-3-vernon2gm@gmail.com> Content-Language: en-US From: Dev Jain In-Reply-To: <20260207081613.588598-3-vernon2gm@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: D08B1140004 X-Stat-Signature: r64us683qgm37x43e1u6fnku6w1bteyd X-Rspam-User: X-HE-Tag: 1770542245-594840 X-HE-Meta: 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 H7PS+JN0 JWJFkAA6XC49zKS91K1aqbKmCEbTZBzgx76Zd5PuLI2xy/rr+lyAFrTPewEeoolG7jFLDKUi5GcSNJwDmWhpuQ9gHx2BFgNcLzHjYWgWu5uqZWKcVeYl1kqlwL4UU87eNzOzcGPYaUqQcXs4b9+IPBGYalx53sElYPbGHVbSBn4nrLQ5iH+JXCUpII3Qm1hYeDKOjeQHj4NbClimvz9plYJ7KKofNgVlf7qhB40mYO66tpd5O5iZGdaKsGT2dfPPC0+DbgRov7GAvrTaz02TDLF624Q== 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 07/02/26 1:46 pm, Vernon Yang wrote: > From: Vernon Yang > > Currently, each scan always increases "progress" by HPAGE_PMD_NR, > even if only scanning a single PTE/PMD entry. > > - When only scanning a sigle PTE entry, let me provide a detailed > example: > > static int hpage_collapse_scan_pmd() > { > for (addr = start_addr, _pte = pte; _pte < pte + HPAGE_PMD_NR; > _pte++, addr += PAGE_SIZE) { > pte_t pteval = ptep_get(_pte); > ... > if (pte_uffd_wp(pteval)) { <-- first scan hit > result = SCAN_PTE_UFFD_WP; > goto out_unmap; > } > } > } > > During the first scan, if pte_uffd_wp(pteval) is true, the loop exits > directly. In practice, only one PTE is scanned before termination. > Here, "progress += 1" reflects the actual number of PTEs scanned, but > previously "progress += HPAGE_PMD_NR" always. > > - When the memory has been collapsed to PMD, let me provide a detailed > example: > > 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. > > From trace_mm_khugepaged_scan_pmd and trace_mm_khugepaged_scan_file, the > following statuses were observed, with frequency mentioned next to them: > > SCAN_SUCCEED : 1 > SCAN_EXCEED_SHARED_PTE: 2 > SCAN_PMD_MAPPED : 142 > SCAN_NO_PTE_TABLE : 178 > 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_EXCEED_SHARED_PTE: 2 > SCAN_PMD_MAPPED : 147 > SCAN_NO_PTE_TABLE : 173 > total progress size : 45 MB > Total time : 20 seconds > > Signed-off-by: Vernon Yang > --- > mm/khugepaged.c | 38 ++++++++++++++++++++++++++++---------- > 1 file changed, 28 insertions(+), 10 deletions(-) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 4049234e1c8b..8b68ae3bc2c5 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; > @@ -1240,7 +1243,8 @@ static enum scan_result collapse_huge_page(struct mm_struct *mm, unsigned long a > } > > static enum scan_result hpage_collapse_scan_pmd(struct mm_struct *mm, > - struct vm_area_struct *vma, unsigned long start_addr, bool *mmap_locked, > + struct vm_area_struct *vma, unsigned long start_addr, > + bool *mmap_locked, unsigned int *cur_progress, > struct collapse_control *cc) > { > pmd_t *pmd; > @@ -1256,19 +1260,27 @@ static enum scan_result hpage_collapse_scan_pmd(struct mm_struct *mm, > VM_BUG_ON(start_addr & ~HPAGE_PMD_MASK); > > result = find_pmd_or_thp_or_none(mm, start_addr, &pmd); > - if (result != SCAN_SUCCEED) > + if (result != SCAN_SUCCEED) { > + if (cur_progress) > + *cur_progress = 1; > goto out; > + } > > memset(cc->node_load, 0, sizeof(cc->node_load)); > nodes_clear(cc->alloc_nmask); > pte = pte_offset_map_lock(mm, pmd, start_addr, &ptl); > if (!pte) { > + if (cur_progress) > + *cur_progress = 1; > result = SCAN_NO_PTE_TABLE; > goto out; > } > > for (addr = start_addr, _pte = pte; _pte < pte + HPAGE_PMD_NR; > _pte++, addr += PAGE_SIZE) { > + if (cur_progress) > + *cur_progress += 1; > + > pte_t pteval = ptep_get(_pte); > if (pte_none_or_zero(pteval)) { > ++none_or_zero; > @@ -2288,8 +2300,9 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr, > return result; > } > > -static enum scan_result hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr, > - struct file *file, pgoff_t start, struct collapse_control *cc) > +static enum scan_result hpage_collapse_scan_file(struct mm_struct *mm, > + unsigned long addr, struct file *file, pgoff_t start, > + unsigned int *cur_progress, struct collapse_control *cc) > { > struct folio *folio = NULL; > struct address_space *mapping = file->f_mapping; > @@ -2378,6 +2391,8 @@ static enum scan_result hpage_collapse_scan_file(struct mm_struct *mm, unsigned > cond_resched_rcu(); > } > } > + if (cur_progress) > + *cur_progress = HPAGE_PMD_NR; > rcu_read_unlock(); > > Nit: Could move this at the end of the function. Looks weird before the rcu_read_unlock. Reviewed-by: Dev Jain