From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6F99A32AACB for ; Mon, 2 Mar 2026 09:57:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772445432; cv=none; b=jVKbcGTULSCMl9GJJNRoOjUW6DQw3+FIzvkeM1Jfqwv3yanzxGizYMFWP3b5uqQM692/pIflLvNG9QybZ8HhMdFO/NwLoAPQQiQSdXZrdcw/xZygSAF+Zvvv6/GutHKl9AB8ncAjhu6lijHs8ldNRiqyk7oumLY4x04/OueG3rU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772445432; c=relaxed/simple; bh=KJ7ZX6odt8qAtq2MrpyupKS6itvmSV0FTiZR897rv3c=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=s/ayuNb2vqA4TSTx89YWQoJq+11FsRPQGM2GZVUFAO1njsUrKJZFmbp/asD3/0sD2SxjFX2IsYrMvPn4itsanPQ/WM+4ndqG2jWS8B3VfN2m3qTfP9PZvKES1pdbkNRkUrosiq+wSlCIBIcTkXZi9kiVq9hITRCDqZJoFSbZF8Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=vHLD6xmr; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="vHLD6xmr" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 490DDC19423; Mon, 2 Mar 2026 09:57:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772445432; bh=KJ7ZX6odt8qAtq2MrpyupKS6itvmSV0FTiZR897rv3c=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=vHLD6xmrK7HIH11cWo9h6oeGlPhz5nezys5omuviIDT5iO/lFUTb5idAvLKCbUbT3 pNOa490Zydgvy5YH4r+r5AHGNDJqo7LaeNkatE/z+wIbGVc3YgLbk31om/AJ4tkrF0 364aAiuGRW3PQZRInDjPtVotdRpsYYj9HHFDIRIl7E1Y/jw6VNBIpKvEC0oKfj88/k 3oBWPfndqWWLQLpYaWU35+DRy1a7/w1MLC/wMl9gjk9K02kegOkB4ps3oAQH8GMVMx kACJd68an+796DmGlA0XKGreIYmgU6EEe/tg1MoVgJJzzjEaDP4hUrIfqP8z3YlBLX HMhdk9fx2B9ig== Message-ID: <7f2973f0-0a34-4e4f-8ed6-13c531f77453@kernel.org> Date: Mon, 2 Mar 2026 10:57:03 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 5/6] mm: support batched checking of the young flag for MGLRU To: Baolin Wang , akpm@linux-foundation.org Cc: catalin.marinas@arm.com, will@kernel.org, lorenzo.stoakes@oracle.com, ryan.roberts@arm.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, riel@surriel.com, harry.yoo@oracle.com, jannh@google.com, willy@infradead.org, baohua@kernel.org, dev.jain@arm.com, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, hannes@cmpxchg.org, zhengqi.arch@bytedance.com, shakeel.butt@linux.dev, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit On 2/27/26 10:44, Baolin Wang wrote: > Use the batched helper test_and_clear_young_ptes_notify() to check and clear > the young flag to improve the performance during large folio reclamation when > MGLRU is enabled. > > Meanwhile, we can also support batched checking the young and dirty flag > when MGLRU walks the mm's pagetable to update the folios' generation > counter. Since MGLRU also checks the PTE dirty bit, use folio_pte_batch_flags() > with FPB_MERGE_YOUNG_DIRTY set to detect batches of PTEs for a large folio. > > Then we can remove the ptep_test_and_clear_young_notify() since it has > no users now. > > Note that we also update the 'young' counter and 'mm_stats[MM_LEAF_YOUNG]' counter > with the batched count in the lru_gen_look_around() and walk_pte_range(). However, > the batched operations may inflate these two counters, because in a large folio not > all PTEs may have been accessed. (Additionally, tracking how many PTEs have been > accessed within a large folio is not very meaningful, since the mm core actually > tracks access/dirty on a per-folio basis, not per page). The impact analysis is as > follows: > > 1. The 'mm_stats[MM_LEAF_YOUNG]' counter has no functional impact and is mainly for > debugging. > > 2. The 'young' counter is used to decide whether to place the current PMD entry into the > bloom filters by suitable_to_scan() (so that next time we can check whether it has been > accessed again), which may set the hash bit in the bloom filters for a PMD entry that > hasn’t seen much access. However, bloom filters inherently allow some error, so this > effect appears negligible. Doesn't checkpatch complain about long lines in the patch description? > > Reviewed-by: Rik van Riel > Signed-off-by: Baolin Wang > --- ... > index a5f0a264ad56..a1b3967afe41 100644 > --- a/mm/internal.h > +++ b/mm/internal.h > @@ -1843,10 +1843,4 @@ static inline int pmdp_test_and_clear_young_notify(struct vm_area_struct *vma, > > #endif /* CONFIG_MMU_NOTIFIER */ > > -static inline int ptep_test_and_clear_young_notify(struct vm_area_struct *vma, > - unsigned long addr, pte_t *ptep) > -{ > - return test_and_clear_young_ptes_notify(vma, addr, ptep, 1); > -} > - > #endif /* __MM_INTERNAL_H */ > diff --git a/mm/rmap.c b/mm/rmap.c > index 11cc6171344f..beb423f3e8ec 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -958,25 +958,21 @@ static bool folio_referenced_one(struct folio *folio, > return false; > } > > + if (pvmw.pte && folio_test_large(folio)) { > + const unsigned long end_addr = pmd_addr_end(address, vma->vm_end); > + const unsigned int max_nr = (end_addr - address) >> PAGE_SHIFT; > + pte_t pteval = ptep_get(pvmw.pte); > + > + nr = folio_pte_batch(folio, pvmw.pte, pteval, max_nr); > + ptes += nr; Could we move that "ptes += nr;" just before the "pra->mapcount -= nr;"? Would make the whole thing look less weird (only incrementing "ptes" with large folios). > + } > + > if (lru_gen_enabled() && pvmw.pte) { > - if (lru_gen_look_around(&pvmw)) > + if (lru_gen_look_around(&pvmw, nr)) > referenced++; > } else if (pvmw.pte) { > - if (folio_test_large(folio)) { > - unsigned long end_addr = pmd_addr_end(address, vma->vm_end); > - unsigned int max_nr = (end_addr - address) >> PAGE_SHIFT; > - pte_t pteval = ptep_get(pvmw.pte); > - > - nr = folio_pte_batch(folio, pvmw.pte, > - pteval, max_nr); > - } > - > - ptes += nr; > if (clear_flush_young_ptes_notify(vma, address, pvmw.pte, nr)) > referenced++; > - /* Skip the batched PTEs */ > - pvmw.pte += nr - 1; > - pvmw.address += (nr - 1) * PAGE_SIZE; > } else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) { > if (pmdp_clear_flush_young_notify(vma, address, > pvmw.pmd)) > @@ -995,6 +991,10 @@ static bool folio_referenced_one(struct folio *folio, > page_vma_mapped_walk_done(&pvmw); > break; > } > + > + /* Skip the batched PTEs */ > + pvmw.pte += nr - 1; > + pvmw.address += (nr - 1) * PAGE_SIZE; > } > > if (referenced) > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 0a5622420987..7457b3c06fa3 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -3474,6 +3474,7 @@ static bool walk_pte_range(pmd_t *pmd, unsigned long start, unsigned long end, > struct pglist_data *pgdat = lruvec_pgdat(walk->lruvec); > DEFINE_MAX_SEQ(walk->lruvec); > int gen = lru_gen_from_seq(max_seq); > + unsigned int nr; > pmd_t pmdval; > > pte = pte_offset_map_rw_nolock(args->mm, pmd, start & PMD_MASK, &pmdval, &ptl); > @@ -3492,11 +3493,13 @@ static bool walk_pte_range(pmd_t *pmd, unsigned long start, unsigned long end, > > lazy_mmu_mode_enable(); > restart: > - for (i = pte_index(start), addr = start; addr != end; i++, addr += PAGE_SIZE) { > + for (i = pte_index(start), addr = start; addr != end; i += nr, addr += nr * PAGE_SIZE) { > unsigned long pfn; > struct folio *folio; > - pte_t ptent = ptep_get(pte + i); > + pte_t *cur_pte = pte + i; > + pte_t ptent = ptep_get(cur_pte); > > + nr = 1; Looking at this again, we should get rid of "i" completely and instead * rename pte to start_pte * Add a new pte, which we increment in the loop So we end up with something like diff --git a/mm/vmscan.c b/mm/vmscan.c index 54cf4924d223..150cbb2253b9 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -3486,9 +3486,8 @@ static void walk_update_folio(struct lru_gen_mm_walk *walk, struct folio *folio, static bool walk_pte_range(pmd_t *pmd, unsigned long start, unsigned long end, struct mm_walk *args) { - int i; bool dirty; - pte_t *pte; + pte_t *start_pte, pte; spinlock_t *ptl; unsigned long addr; int total = 0; @@ -3499,29 +3498,31 @@ static bool walk_pte_range(pmd_t *pmd, unsigned long start, unsigned long end, struct pglist_data *pgdat = lruvec_pgdat(walk->lruvec); DEFINE_MAX_SEQ(walk->lruvec); int gen = lru_gen_from_seq(max_seq); + unsigned int nr; pmd_t pmdval; - pte = pte_offset_map_rw_nolock(args->mm, pmd, start & PMD_MASK, &pmdval, &ptl); - if (!pte) + start_pte = pte_offset_map_rw_nolock(args->mm, pmd, start & PMD_MASK, &pmdval, &ptl); + if (!start_pte) return false; if (!spin_trylock(ptl)) { - pte_unmap(pte); + pte_unmap(start_pte); return true; } if (unlikely(!pmd_same(pmdval, pmdp_get_lockless(pmd)))) { - pte_unmap_unlock(pte, ptl); + pte_unmap_unlock(start_pte, ptl); return false; } lazy_mmu_mode_enable(); restart: - for (i = pte_index(start), addr = start; addr != end; i++, addr += PAGE_SIZE) { + for (addr = start, pte = start_pte; addr != end; addr += nr * PAGE_SIZE, pte += nr) { unsigned long pfn; struct folio *folio; - pte_t ptent = ptep_get(pte + i); + pte_t ptent = ptep_get(pte); + nr = 1; total++; walk->mm_stats[MM_LEAF_TOTAL]++; @@ -3533,7 +3534,16 @@ static bool walk_pte_range(pmd_t *pmd, unsigned long start, unsigned long end, if (!folio) continue; ... > walk_update_folio(walk, last, gen, dirty); > @@ -4166,7 +4178,7 @@ static void lru_gen_age_node(struct pglist_data *pgdat, struct scan_control *sc) > * the PTE table to the Bloom filter. This forms a feedback loop between the > * eviction and the aging. > */ > -bool lru_gen_look_around(struct page_vma_mapped_walk *pvmw) > +bool lru_gen_look_around(struct page_vma_mapped_walk *pvmw, unsigned int nr) > { > int i; > bool dirty; > @@ -4184,12 +4196,13 @@ bool lru_gen_look_around(struct page_vma_mapped_walk *pvmw) > struct lruvec *lruvec; > struct lru_gen_mm_state *mm_state; > unsigned long max_seq; > + pte_t *cur_pte; > int gen; > > lockdep_assert_held(pvmw->ptl); > VM_WARN_ON_ONCE_FOLIO(folio_test_lru(folio), folio); > > - if (!ptep_test_and_clear_young_notify(vma, addr, pte)) > + if (!test_and_clear_young_ptes_notify(vma, addr, pte, nr)) > return false; > > if (spin_is_contended(pvmw->ptl)) > @@ -4229,10 +4242,12 @@ bool lru_gen_look_around(struct page_vma_mapped_walk *pvmw) > > pte -= (addr - start) / PAGE_SIZE; > > - for (i = 0, addr = start; addr != end; i++, addr += PAGE_SIZE) { > + for (i = 0, addr = start, cur_pte = pte; addr != end; > + i += nr, cur_pte += nr, addr += nr * PAGE_SIZE) { > unsigned long pfn; > - pte_t ptent = ptep_get(pte + i); > + pte_t ptent = ptep_get(cur_pte); > > + nr = 1; Can't you just use pte and increment that, right? "pte" is not used afterwards. -- Cheers, David