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Fri, 16 Jan 2026 20:18:31 -0800 (PST) Received: from localhost.localdomain ([221.227.246.159]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-81fa12b49e0sm3204897b3a.67.2026.01.16.20.18.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 16 Jan 2026 20:18:30 -0800 (PST) Date: Sat, 17 Jan 2026 12:18:20 +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, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Vernon Yang Subject: Re: [PATCH mm-new v4 2/6] mm: khugepaged: refine scan progress number Message-ID: References: <20260111121909.8410-1-yanglincheng@kylinos.cn> <20260111121909.8410-3-yanglincheng@kylinos.cn> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 75C71C0006 X-Stat-Signature: 394cpgu71zekzudu1y5w13htskorrwmc X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1768623512-300973 X-HE-Meta: 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 U5rBo2tc L9ZhmxheWWVTflGCpFVKSKXopj8POxGTJNMiEiPCn2fIxVSYHhdv/dZVN98LfwpwoxyVaI8tPdYNLw7YGWg8OJGu+JU5kF3FJkQF3jh1Aemr4nja3OQ8bXGzxRoqF+slChv+aMcBZ8x8XZdDYmhgidek8nNbnBMTyQ6B8KVaRl+QGRZzV1DjLHXLaUIaDc6ed0f5uP2f6hnnKm+oN5+FhLZNGcjR9hlB8af2HcFFqmmRDV4ne1TbXtVR2udi+BZ5eS3UWgFxQd0cyaKK5VyCK2N3wQVOk5KQOIO60T9kfoRuuuFW/D0nXdB/K4efO6JJ2BmlQ+fTcfJFhw993tjtmHAetqCJ2zaGdTLH17+xdSIYqfZwl5vuXm5oChg2c4yI8jJh+YrvHxa8ESow/VkkwvRkjMD0e0EzmSIX0aqa6Vt4eCAkyYRG0TxRs1ClkE504SeDqsmd+LE5EowKfUrUoDgSJAQ== 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 Wed, Jan 14, 2026 at 12:38:46PM +0100, David Hildenbrand (Red Hat) wrote: > On 1/11/26 13:19, Vernon Yang wrote: > > Currently, each scan always increases "progress" by HPAGE_PMD_NR, > > even if only scanning a single pte. > > > > 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) { > > 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. > > > > Signed-off-by: Vernon Yang > > --- > > mm/khugepaged.c | 28 ++++++++++++++++++++++------ > > 1 file changed, 22 insertions(+), 6 deletions(-) > > > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > > index 2e570f83778c..5c6015ac7b5e 100644 > > --- a/mm/khugepaged.c > > +++ b/mm/khugepaged.c > > @@ -1249,6 +1249,7 @@ 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, > > + int *cur_progress, > > struct collapse_control *cc) > > { > > pmd_t *pmd; > > @@ -1264,19 +1265,27 @@ 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 = 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; > > @@ -2297,6 +2306,7 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr, > > static enum scan_result 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; > > @@ -2337,6 +2347,9 @@ static enum scan_result hpage_collapse_scan_file(struct mm_struct *mm, unsigned > > continue; > > } > > + if (cur_progress) > > + *cur_progress += folio_nr_pages(folio); > > + > > Okay, I had another look and I think the file path is confusing. We're > scanning xarray entries. But then, we only count some entries and not > others. Thank you for the review. Move PATCH #3 comments here > Assume we found a single 4k folio in the xarray, but then collapse a 2M THP. > Is the progress really "1" ? This example is indeed a issue, I will use "xas->xa_index" to fix these issues. > What about shmem swap entries (xa_is_value)? Sorry, I missed it. I will add "1 << xas_get_order(&xas)" to "cur_progreess". > Can we just keep that alone in this patch? That is, always indicate a > progress of HPAGE_PMD_NR right at the start of the function? Studying the implementation source code of xarray, I discovered that these issues can be fixed by utilizing "xas->xa_index". I send the code as follow (patch #2 and #3 are squashed). Let's see if it works? If not, please let me know, Thanks! -- Thanks, Vernon diff --git a/include/linux/xarray.h b/include/linux/xarray.h index be850174e802..f77d97d7b957 100644 --- a/include/linux/xarray.h +++ b/include/linux/xarray.h @@ -1646,6 +1646,15 @@ static inline void xas_set(struct xa_state *xas, unsigned long index) xas->xa_node = XAS_RESTART; } +/** + * xas_get_index() - Get XArray operation state for a different index. + * @xas: XArray operation state. + */ +static inline unsigned long xas_get_index(struct xa_state *xas) +{ + return xas->xa_index; +} + /** * xas_advance() - Skip over sibling entries. * @xas: XArray operation state. diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 2e570f83778c..7d42035ece5b 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; @@ -1249,6 +1252,7 @@ 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, + unsigned int *cur_progress, struct collapse_control *cc) { pmd_t *pmd; @@ -1263,6 +1267,9 @@ static enum scan_result hpage_collapse_scan_pmd(struct mm_struct *mm, VM_BUG_ON(start_addr & ~HPAGE_PMD_MASK); + if (cur_progress) + *cur_progress += 1; + result = find_pmd_or_thp_or_none(mm, start_addr, &pmd); if (result != SCAN_SUCCEED) goto out; @@ -1403,6 +1410,8 @@ static enum scan_result hpage_collapse_scan_pmd(struct mm_struct *mm, } else { result = SCAN_SUCCEED; } + if (cur_progress) + *cur_progress += _pte - pte; out_unmap: pte_unmap_unlock(pte, ptl); if (result == SCAN_SUCCEED) { @@ -2297,6 +2306,7 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr, 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; @@ -2386,6 +2396,18 @@ static enum scan_result hpage_collapse_scan_file(struct mm_struct *mm, unsigned cond_resched_rcu(); } } + if (cur_progress) { + unsigned long idx = xas_get_index(&xas) - start; + + if (folio == NULL) + *cur_progress += HPAGE_PMD_NR; + else if (xa_is_value(folio)) + *cur_progress += idx + (1 << xas_get_order(&xas)); + else if (folio_order(folio) == HPAGE_PMD_ORDER) + *cur_progress += idx + 1; + else + *cur_progress += idx + folio_nr_pages(folio); + } rcu_read_unlock(); if (result == SCAN_SUCCEED) { @@ -2466,6 +2488,7 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, enum scan_result while (khugepaged_scan.address < hend) { bool mmap_locked = true; + unsigned int cur_progress = 0; cond_resched(); if (unlikely(hpage_collapse_test_exit_or_disable(mm))) @@ -2482,7 +2505,8 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, enum scan_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); @@ -2496,7 +2520,8 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, enum scan_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) @@ -2504,7 +2529,7 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, enum scan_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 @@ -2826,11 +2851,11 @@ 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;