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[2003:cb:c74b:bf00:182c:d606:87cf:6fea]) by smtp.gmail.com with ESMTPSA id b12-20020a5d4d8c000000b0034e65b8b43fsm8552835wru.8.2024.05.06.05.07.28 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 06 May 2024 05:07:29 -0700 (PDT) Message-ID: Date: Mon, 6 May 2024 14:07:28 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 6/6] mm: swap: entirely map large folios found in swapcache To: Barry Song <21cnbao@gmail.com>, Ryan Roberts Cc: akpm@linux-foundation.org, linux-mm@kvack.org, baolin.wang@linux.alibaba.com, chrisl@kernel.org, hanchuanhua@oppo.com, hannes@cmpxchg.org, hughd@google.com, kasong@tencent.com, linux-kernel@vger.kernel.org, surenb@google.com, v-songbaohua@oppo.com, willy@infradead.org, xiang@kernel.org, ying.huang@intel.com, yosryahmed@google.com, yuzhao@google.com, ziy@nvidia.com References: <20240503005023.174597-1-21cnbao@gmail.com> <20240503005023.174597-7-21cnbao@gmail.com> <0b4d4d4b-91d8-4fd5-af4e-aebe9ee08b89@arm.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Stat-Signature: qbowwmsxji6oebxuy9bkq58karueewsh X-Rspam-User: X-Rspamd-Queue-Id: BBEF5C000F X-Rspamd-Server: rspam05 X-HE-Tag: 1714997253-850838 X-HE-Meta: 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 f3WB1MCs 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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 04.05.24 01:23, Barry Song wrote: > On Fri, May 3, 2024 at 6:50 PM Ryan Roberts wrote: >> >> On 03/05/2024 01:50, Barry Song wrote: >>> From: Chuanhua Han >>> >>> When a large folio is found in the swapcache, the current implementation >>> requires calling do_swap_page() nr_pages times, resulting in nr_pages >>> page faults. This patch opts to map the entire large folio at once to >>> minimize page faults. Additionally, redundant checks and early exits >>> for ARM64 MTE restoring are removed. >>> >>> Signed-off-by: Chuanhua Han >>> Co-developed-by: Barry Song >>> Signed-off-by: Barry Song >> >> With the suggested changes below: >> >> Reviewed-by: Ryan Roberts >> >>> --- >>> mm/memory.c | 60 ++++++++++++++++++++++++++++++++++++++++++----------- >>> 1 file changed, 48 insertions(+), 12 deletions(-) >>> >>> diff --git a/mm/memory.c b/mm/memory.c >>> index 22e7c33cc747..940fdbe69fa1 100644 >>> --- a/mm/memory.c >>> +++ b/mm/memory.c >>> @@ -3968,6 +3968,10 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) >>> pte_t pte; >>> vm_fault_t ret = 0; >>> void *shadow = NULL; >>> + int nr_pages = 1; >>> + unsigned long page_idx = 0; >>> + unsigned long address = vmf->address; >>> + pte_t *ptep; >> >> nit: Personally I'd prefer all these to get initialised just before the "if >> (folio_test_large()..." block below. That way it is clear they are fresh (incase >> any logic between here and there makes an adjustment) and its clear that they >> are only to be used after that block (the compiler will warn if using an >> uninitialized value). > > right. I agree this will make the code more readable. > >> >>> >>> if (!pte_unmap_same(vmf)) >>> goto out; >>> @@ -4166,6 +4170,36 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) >>> goto out_nomap; >>> } >>> >>> + ptep = vmf->pte; >>> + if (folio_test_large(folio) && folio_test_swapcache(folio)) { >>> + int nr = folio_nr_pages(folio); >>> + unsigned long idx = folio_page_idx(folio, page); >>> + unsigned long folio_start = vmf->address - idx * PAGE_SIZE; >>> + unsigned long folio_end = folio_start + nr * PAGE_SIZE; >>> + pte_t *folio_ptep; >>> + pte_t folio_pte; >>> + >>> + if (unlikely(folio_start < max(vmf->address & PMD_MASK, vma->vm_start))) >>> + goto check_folio; >>> + if (unlikely(folio_end > pmd_addr_end(vmf->address, vma->vm_end))) >>> + goto check_folio; >>> + >>> + folio_ptep = vmf->pte - idx; >>> + folio_pte = ptep_get(folio_ptep); >>> + if (!pte_same(folio_pte, pte_move_swp_offset(vmf->orig_pte, -idx)) || >>> + swap_pte_batch(folio_ptep, nr, folio_pte) != nr) >>> + goto check_folio; >>> + >>> + page_idx = idx; >>> + address = folio_start; >>> + ptep = folio_ptep; >>> + nr_pages = nr; >>> + entry = folio->swap; >>> + page = &folio->page; >>> + } >>> + >>> +check_folio: >> >> Is this still the correct label name, given the checks are now above the new >> block? Perhaps "one_page" or something like that? > > not quite sure about this, as the code after one_page can be multiple_pages. > On the other hand, it seems we are really checking folio after "check_folio" > :-) > > > BUG_ON(!folio_test_anon(folio) && folio_test_mappedtodisk(folio)); > BUG_ON(folio_test_anon(folio) && PageAnonExclusive(page)); > > /* > * Check under PT lock (to protect against concurrent fork() sharing > * the swap entry concurrently) for certainly exclusive pages. > */ > if (!folio_test_ksm(folio)) { > > >> >>> + >>> /* >>> * PG_anon_exclusive reuses PG_mappedtodisk for anon pages. A swap pte >>> * must never point at an anonymous page in the swapcache that is >>> @@ -4225,12 +4259,13 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) >>> * We're already holding a reference on the page but haven't mapped it >>> * yet. >>> */ >>> - swap_free_nr(entry, 1); >>> + swap_free_nr(entry, nr_pages); >>> if (should_try_to_free_swap(folio, vma, vmf->flags)) >>> folio_free_swap(folio); >>> >>> - inc_mm_counter(vma->vm_mm, MM_ANONPAGES); >>> - dec_mm_counter(vma->vm_mm, MM_SWAPENTS); >>> + folio_ref_add(folio, nr_pages - 1); >>> + add_mm_counter(vma->vm_mm, MM_ANONPAGES, nr_pages); >>> + add_mm_counter(vma->vm_mm, MM_SWAPENTS, -nr_pages); >>> pte = mk_pte(page, vma->vm_page_prot); >>> >>> /* >>> @@ -4240,34 +4275,35 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) >>> * exclusivity. >>> */ >>> if (!folio_test_ksm(folio) && >>> - (exclusive || folio_ref_count(folio) == 1)) { >>> + (exclusive || (folio_ref_count(folio) == nr_pages && >>> + folio_nr_pages(folio) == nr_pages))) { >> >> I think in practice there is no change here? If nr_pages > 1 then the folio is >> in the swapcache, so there is an extra ref on it? I agree with the change for >> robustness sake. Just checking my understanding. > > This is the code showing we are reusing/(mkwrite) a folio either > 1. we meet a small folio and we are the only one hitting the small folio > 2. we meet a large folio and we are the only one hitting the large folio > > any corner cases besides the above two seems difficult. for example, > > while we hit a large folio in swapcache but if we can't entirely map it > (nr_pages==1) due to partial unmap, we will have folio_ref_count(folio) > == nr_pages == 1 No, there would be other references from the swapcache and folio_ref_count(folio) > 1. See my other reply. -- Cheers, David / dhildenb