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a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772095365; bh=zW1s9sD5DWBrMAAEnEuYwmxFxQgWMEFNnLPq3VWI4IE=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=J/Ix/T8PGmmSZU01h8WvC2LXp7Jy4EzeUmUVK9WZ3NHKLI6N0XasbpDQy+8Cg7uuZ hGFKRvG8ikHbexZEyl26eex9mjVUOzSo61yUoJaBYXiW/9Qac4Z0wZyqtTq/Wo/TB3 hYImKmmyKXW1RGbwI6n/tvyJt2aa1cvdlARcCBHAqaOcQrEbj3HcfflyvIyw0gF5nz nVHWy46sptFfPGCha7tEpSyt2U+xH/mwSd0yGzEh43MbcWUreV+/Wui07vrpJQ5B0h RJZsXtLZsDmVCDlh19mr1625e8u04uqmgfgaq7OdyOMkKFEiRDn/tbI45ulDhZCM88 oUtsByduHNyqw== Message-ID: <06ff4738-e81a-49ab-9204-74a6829d8d8b@kernel.org> Date: Thu, 26 Feb 2026 09:42:41 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: khugepaged: simplify scanning progress in pmd To: Vernon Yang , akpm@linux-foundation.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 References: <20260226081313.53518-1-vernon2gm@gmail.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: CA66C1C0002 X-Stat-Signature: de4gkcoewhojdxfmwwhb5g1c5wnqi3b9 X-HE-Tag: 1772095366-138229 X-HE-Meta: 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 29BkjUd0 U32jDXh66EWSHhJVCBe//JPIK/aC4Aq0w2O2sGO6hVHUEYjBB8LiSGTf9uhg3ox1wZ444nZ4SAI0h/LeGYIIsd4+5v4OsRTXqa/oF2SV1r0JNoWDiBBgcBZxHIh2Z9t8rA0a5K1jq+jWuhhTPe804hNAw0CLoCSKIT2rgx4SJR7G9n+2HS7GljOzfSY/96hkLcSLSapSDGSqH1Cv3udzLJkyet7Dk9JoIzW+QCWTB9Ft0UVTxrQDP++/Kqm5AXw5csHd4HOxybCVydSnAVTTI3jJggtHpJuUhFwPVfYPtkwPDGOKWrSHuZ+yzQJlxsgSyy8uwpwoy7eZPkKkBniPggWaIm67xS0g7HsBLVbB0V8cQUJA= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2/26/26 09:13, Vernon Yang wrote: > From: Vernon Yang > > Placing "cur_progress" inside "struct collapse_control" makes the > overall code simpler, there also coincidentally has a 4-bytes hole, > as shown below: > > struct collapse_control { > bool is_khugepaged; /* 0 1 */ > /* XXX 3 bytes hole, try to pack */ > u32 node_load[64]; /* 4 256 */ > /* XXX 4 bytes hole, try to pack */ > /* --- cacheline 4 boundary (256 bytes) was 8 bytes ago --- */ > nodemask_t alloc_nmask; /* 264 8 */ > > /* size: 272, cachelines: 5, members: 3 */ > /* sum members: 265, holes: 2, sum holes: 7 */ > /* last cacheline: 16 bytes */ > }; > > Also rename "cur_progress" to "progress_in_pmd", make it clearer. > > No function changes. > > Signed-off-by: Vernon Yang > --- We should really squash that into the original patch and revisit it. Because I think we might be able to do even better. Could we just switch to "cc->progress" like so (modified original patch): diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 4d7baf220ad9..5d67e5e60ece 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, pte_mapped_hugepage, 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; @@ -100,6 +103,9 @@ struct collapse_control { /* Num pages scanned per node */ u32 node_load[MAX_NUMNODES]; + /* Num pages scanned (see khugepaged_pages_to_scan). */ + unsigned int progress; + /* nodemask for allocation fallback */ nodemask_t alloc_nmask; }; @@ -1247,19 +1253,24 @@ 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) { + cc->progress++; 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) { + cc->progress++; result = SCAN_NO_PTE_TABLE; goto out; } for (addr = start_addr, _pte = pte; _pte < pte + HPAGE_PMD_NR; _pte++, addr += PAGE_SIZE) { + cc->progress++; + pte_t pteval = ptep_get(_pte); if (pte_none_or_zero(pteval)) { ++none_or_zero; @@ -2370,6 +2381,10 @@ static enum scan_result hpage_collapse_scan_file(struct mm_struct *mm, unsigned } } rcu_read_unlock(); + if (result == SCAN_PTE_MAPPED_HUGEPAGE) + cc->progress++; + else + cc->progress += HPAGE_PMD_NR; if (result == SCAN_SUCCEED) { if (cc->is_khugepaged && @@ -2385,8 +2400,8 @@ static enum scan_result hpage_collapse_scan_file(struct mm_struct *mm, unsigned return result; } -static unsigned int khugepaged_scan_mm_slot(unsigned int pages, enum scan_result *result, - struct collapse_control *cc) +static void khugepaged_scan_mm_slot(unsigned int progress_max, + enum scan_result *result, struct collapse_control *cc) __releases(&khugepaged_mm_lock) __acquires(&khugepaged_mm_lock) { @@ -2394,9 +2409,7 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, enum scan_result struct mm_slot *slot; struct mm_struct *mm; struct vm_area_struct *vma; - int progress = 0; - VM_BUG_ON(!pages); lockdep_assert_held(&khugepaged_mm_lock); *result = SCAN_FAIL; @@ -2419,7 +2432,7 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, enum scan_result if (unlikely(!mmap_read_trylock(mm))) goto breakouterloop_mmap_lock; - progress++; + cc->progress++; if (unlikely(hpage_collapse_test_exit_or_disable(mm))) goto breakouterloop; @@ -2429,17 +2442,17 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, enum scan_result cond_resched(); if (unlikely(hpage_collapse_test_exit_or_disable(mm))) { - progress++; + cc->progress++; break; } if (!thp_vma_allowable_order(vma, vma->vm_flags, TVA_KHUGEPAGED, PMD_ORDER)) { - progress++; + cc->progress++; continue; } hstart = round_up(vma->vm_start, HPAGE_PMD_SIZE); hend = round_down(vma->vm_end, HPAGE_PMD_SIZE); if (khugepaged_scan.address > hend) { - progress++; + cc->progress++; continue; } if (khugepaged_scan.address < hstart) @@ -2486,7 +2499,6 @@ 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; if (!mmap_locked) /* * We released mmap_lock so break loop. Note @@ -2496,7 +2508,7 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, enum scan_result * correct result back to caller. */ goto breakouterloop_mmap_lock; - if (progress >= pages) + if (cc->progress >= progress_max) goto breakouterloop; } } @@ -2527,9 +2539,7 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, enum scan_result collect_mm_slot(slot); } - trace_mm_khugepaged_scan(mm, progress, khugepaged_scan.mm_slot == NULL); - - return progress; + trace_mm_khugepaged_scan(mm, cc->progress, khugepaged_scan.mm_slot == NULL); } static int khugepaged_has_work(void) @@ -2545,13 +2555,14 @@ static int khugepaged_wait_event(void) static void khugepaged_do_scan(struct collapse_control *cc) { - unsigned int progress = 0, pass_through_head = 0; - unsigned int pages = READ_ONCE(khugepaged_pages_to_scan); + const unsigned int progress_max = READ_ONCE(khugepaged_pages_to_scan); + unsigned int pass_through_head = 0; bool wait = true; enum scan_result result = SCAN_SUCCEED; lru_add_drain_all(); + cc->progress = 0; while (true) { cond_resched(); @@ -2563,13 +2574,12 @@ static void khugepaged_do_scan(struct collapse_control *cc) pass_through_head++; if (khugepaged_has_work() && pass_through_head < 2) - progress += khugepaged_scan_mm_slot(pages - progress, - &result, cc); + khugepaged_scan_mm_slot(progress_max, &result, cc); else - progress = pages; + cc->progress = progress_max; spin_unlock(&khugepaged_mm_lock); - if (progress >= pages) + if (cc->progress >= progress_max) break; if (result == SCAN_ALLOC_HUGE_PAGE_FAIL) { -- 2.43.0 -- Cheers, David