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Mon, 05 Jan 2026 21:56:01 -0800 (PST) Received: from localhost.localdomain ([121.232.80.251]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-819c5302c61sm877571b3a.42.2026.01.05.21.55.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 05 Jan 2026 21:56:00 -0800 (PST) Date: Tue, 6 Jan 2026 13:55:44 +0800 From: Vernon Yang To: "David Hildenbrand (Red Hat)" Cc: akpm@linux-foundation.org, 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: Re: [PATCH v3 2/6] mm: khugepaged: refine scan progress number Message-ID: References: <20260104054112.4541-1-yanglincheng@kylinos.cn> <20260104054112.4541-3-yanglincheng@kylinos.cn> <69c9ac59-4fb2-42fc-a8ae-32f583e47de4@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <69c9ac59-4fb2-42fc-a8ae-32f583e47de4@kernel.org> X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: A97B580009 X-Stat-Signature: ytss6khwui9ofma76dax75knwis6dt3y X-Rspam-User: X-HE-Tag: 1767678962-847239 X-HE-Meta: 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 OdoZJkoH 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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 Mon, Jan 05, 2026 at 05:49:22PM +0100, David Hildenbrand (Red Hat) wrote: > On 1/4/26 06:41, Vernon Yang wrote: > > Currently, each PMD scan always increases `progress` by HPAGE_PMD_NR, > > even if only scanning a single page. By counting the actual number of > > "... a single pmd" ? > > > pages scanned, the `progress` is tracked accurately. > > "page table entries / pages scanned" ? The single page is pte-4KB only. This patch does not change the original semantics of "progress", it simply uses the exact number of PTEs counted to replace HPAGE_PMD_NR. 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) { _progress++; 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. Previously discussed, just skip SCAN_PMD_MAPPED or SCAN_NO_PTE_TABLE, currently in Patch #3, not this Patch #2. > > > > Signed-off-by: Vernon Yang > > --- > > mm/khugepaged.c | 31 +++++++++++++++++++++++-------- > > 1 file changed, 23 insertions(+), 8 deletions(-) > > > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > > index 9f99f61689f8..4b124e854e2e 100644 > > --- a/mm/khugepaged.c > > +++ b/mm/khugepaged.c > > @@ -1247,7 +1247,7 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address, > > static int hpage_collapse_scan_pmd(struct mm_struct *mm, > > struct vm_area_struct *vma, > > unsigned long start_addr, bool *mmap_locked, > > - struct collapse_control *cc) > > + int *progress, struct collapse_control *cc) > > { > > pmd_t *pmd; > > pte_t *pte, *_pte; > > @@ -1258,23 +1258,28 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm, > > unsigned long addr; > > spinlock_t *ptl; > > int node = NUMA_NO_NODE, unmapped = 0; > > + int _progress = 0; > > "cur_progress" ? Yes. > > 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) { > > + _progress = HPAGE_PMD_NR; > > 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) { > > + _progress = HPAGE_PMD_NR; > > result = SCAN_NO_PTE_TABLE; > > goto out; > > } > > for (addr = start_addr, _pte = pte; _pte < pte + HPAGE_PMD_NR; > > _pte++, addr += PAGE_SIZE) { > > + _progress++; > > pte_t pteval = ptep_get(_pte); > > if (pte_none_or_zero(pteval)) { > > ++none_or_zero; > > @@ -1410,6 +1415,9 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm, > > *mmap_locked = false; > > } > > out: > > + if (progress) > > + *progress += _progress; > > + > > trace_mm_khugepaged_scan_pmd(mm, folio, referenced, > > none_or_zero, result, unmapped); > > return result; > > @@ -2287,7 +2295,7 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr, > > static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr, > > struct file *file, pgoff_t start, > > - struct collapse_control *cc) > > + int *progress, struct collapse_control *cc) > > { > > struct folio *folio = NULL; > > struct address_space *mapping = file->f_mapping; > > @@ -2295,6 +2303,7 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr, > > int present, swap; > > int node = NUMA_NO_NODE; > > int result = SCAN_SUCCEED; > > + int _progress = 0; > > Same here. > > > Not sure if it would be cleaner to just let the parent increment its counter > and returning instead the "cur_progress" from the function. Both are good for me, I have implemented one version as follows, please see if it is cleaner. -- Thanks, Vernon diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 9f99f61689f8..4cf24553c2bd 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -1247,6 +1247,7 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address, static int hpage_collapse_scan_pmd(struct mm_struct *mm, struct vm_area_struct *vma, unsigned long start_addr, bool *mmap_locked, + int *cur_progress, struct collapse_control *cc) { pmd_t *pmd; @@ -1262,19 +1263,27 @@ static int 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 = HPAGE_PMD_NR; 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 = HPAGE_PMD_NR; 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; @@ -2287,6 +2296,7 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr, static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr, struct file *file, pgoff_t start, + int *cur_progress, struct collapse_control *cc) { struct folio *folio = NULL; @@ -2327,6 +2337,9 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr, continue; } + if (cur_progress) + *cur_progress += folio_nr_pages(folio); + if (folio_order(folio) == HPAGE_PMD_ORDER && folio->index == start) { /* Maybe PMD-mapped */ @@ -2454,6 +2467,7 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result, while (khugepaged_scan.address < hend) { bool mmap_locked = true; + int cur_progress = 0; cond_resched(); if (unlikely(hpage_collapse_test_exit_or_disable(mm))) @@ -2470,7 +2484,8 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result, mmap_read_unlock(mm); mmap_locked = false; *result = hpage_collapse_scan_file(mm, - khugepaged_scan.address, file, pgoff, cc); + khugepaged_scan.address, file, pgoff, + &cur_progress, cc); fput(file); if (*result == SCAN_PTE_MAPPED_HUGEPAGE) { mmap_read_lock(mm); @@ -2484,7 +2499,8 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result, } } else { *result = hpage_collapse_scan_pmd(mm, vma, - khugepaged_scan.address, &mmap_locked, cc); + khugepaged_scan.address, &mmap_locked, + &cur_progress, cc); } if (*result == SCAN_SUCCEED) @@ -2492,7 +2508,7 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result, /* move to next address */ khugepaged_scan.address += HPAGE_PMD_SIZE; - progress += HPAGE_PMD_NR; + progress += cur_progress; if (!mmap_locked) /* * We released mmap_lock so break loop. Note @@ -2810,11 +2826,11 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, mmap_read_unlock(mm); mmap_locked = false; result = hpage_collapse_scan_file(mm, addr, file, pgoff, - cc); + NULL, cc); fput(file); } else { result = hpage_collapse_scan_pmd(mm, vma, addr, - &mmap_locked, cc); + &mmap_locked, NULL, cc); } if (!mmap_locked) *lock_dropped = true;