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[2003:cb:c740:2200:95d8:cbf4:fffd:7f81]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3609aa60a59sm1739171f8f.84.2024.06.17.11.04.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 17 Jun 2024 11:04:44 -0700 (PDT) Message-ID: Date: Mon, 17 Jun 2024 20:04:42 +0200 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 v8 3/3] mm/vmscan: avoid split lazyfree THP during shrink_folio_list() To: Lance Yang , akpm@linux-foundation.org Cc: willy@infradead.org, sj@kernel.org, baolin.wang@linux.alibaba.com, maskray@google.com, ziy@nvidia.com, ryan.roberts@arm.com, 21cnbao@gmail.com, mhocko@suse.com, fengwei.yin@intel.com, zokeefe@google.com, shy828301@gmail.com, xiehuan09@gmail.com, libang.li@antgroup.com, wangkefeng.wang@huawei.com, songmuchun@bytedance.com, peterx@redhat.com, minchan@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20240614015138.31461-1-ioworker0@gmail.com> <20240614015138.31461-4-ioworker0@gmail.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: <20240614015138.31461-4-ioworker0@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sorry for taking so long to review ... getting there. Mostly nits. > @@ -497,6 +499,13 @@ static inline void split_huge_pmd_locked(struct vm_area_struct *vma, > unsigned long address, pmd_t *pmd, > bool freeze, struct folio *folio) {} > > +static inline bool unmap_huge_pmd_locked(struct vm_area_struct *vma, > + unsigned long addr, pmd_t *pmdp, > + struct folio *folio) > +{ > + return false; > +} > + > #define split_huge_pud(__vma, __pmd, __address) \ > do { } while (0) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index e766d3f3a302..425374ae06ed 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -2688,6 +2688,82 @@ static void unmap_folio(struct folio *folio) > try_to_unmap_flush(); > } > > +static bool __discard_anon_folio_pmd_locked(struct vm_area_struct *vma, > + unsigned long addr, pmd_t *pmdp, > + struct folio *folio) > +{ > + VM_WARN_ON_FOLIO(folio_test_swapbacked(folio), folio); > + VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio); I would drop these (that's exactly what the single caller checks). In any case don't place them above the variable declaration ;) > + > + struct mm_struct *mm = vma->vm_mm; > + int ref_count, map_count; > + pmd_t orig_pmd = *pmdp; > + struct page *page; > + > + if (unlikely(!pmd_present(orig_pmd) || !pmd_trans_huge(orig_pmd))) > + return false; > + > + page = pmd_page(orig_pmd); > + if (unlikely(page_folio(page) != folio)) > + return false; I'm curious, how could that happen? And how could it happen that we have !pmd_trans_huge() ? Didn't rmap walking code make sure that this PMD maps the folio already, and we are holding the PTL? > + > + if (folio_test_dirty(folio) || pmd_dirty(orig_pmd)) > + return false; > + > + orig_pmd = pmdp_huge_clear_flush(vma, addr, pmdp); > + > + /* > + * Syncing against concurrent GUP-fast: > + * - clear PMD; barrier; read refcount > + * - inc refcount; barrier; read PMD > + */ > + smp_mb(); > + > + ref_count = folio_ref_count(folio); > + map_count = folio_mapcount(folio); > + > + /* > + * Order reads for folio refcount and dirty flag > + * (see comments in __remove_mapping()). > + */ > + smp_rmb(); > + > + /* > + * If the folio or its PMD is redirtied at this point, or if there > + * are unexpected references, we will give up to discard this folio > + * and remap it. > + * > + * The only folio refs must be one from isolation plus the rmap(s). > + */ > + if (folio_test_dirty(folio) || pmd_dirty(orig_pmd) || > + ref_count != map_count + 1) { > + set_pmd_at(mm, addr, pmdp, orig_pmd); > + return false; > + } > + > + folio_remove_rmap_pmd(folio, page, vma); > + zap_deposited_table(mm, pmdp); > + add_mm_counter(mm, MM_ANONPAGES, -HPAGE_PMD_NR); > + if (vma->vm_flags & VM_LOCKED) > + mlock_drain_local(); > + folio_put(folio); > + > + return true; > +} > + > +bool unmap_huge_pmd_locked(struct vm_area_struct *vma, unsigned long addr, > + pmd_t *pmdp, struct folio *folio) > +{ > + VM_WARN_ON_FOLIO(!folio_test_pmd_mappable(folio), folio); > + VM_WARN_ON_FOLIO(!folio_test_locked(folio), folio); > + VM_WARN_ON_ONCE(!IS_ALIGNED(addr, HPAGE_PMD_SIZE)); > + > + if (folio_test_anon(folio) && !folio_test_swapbacked(folio)) > + return __discard_anon_folio_pmd_locked(vma, addr, pmdp, folio); > + > + return false; > +} > + > static void remap_page(struct folio *folio, unsigned long nr) > { > int i = 0; > diff --git a/mm/rmap.c b/mm/rmap.c > index dacf24bc82f0..7d97806f74cd 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -1678,16 +1678,23 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, > goto walk_abort; > } > > - if (!pvmw.pte && (flags & TTU_SPLIT_HUGE_PMD)) { > - /* > - * We temporarily have to drop the PTL and start once > - * again from that now-PTE-mapped page table. > - */ > - split_huge_pmd_locked(vma, pvmw.address, pvmw.pmd, > - false, folio); > - flags &= ~TTU_SPLIT_HUGE_PMD; > - page_vma_mapped_walk_restart(&pvmw); > - continue; > + if (!pvmw.pte) { > + if (unmap_huge_pmd_locked(vma, pvmw.address, pvmw.pmd, > + folio)) > + goto walk_done; > + > + if (flags & TTU_SPLIT_HUGE_PMD) { > + /* > + * We temporarily have to drop the PTL and start > + * once again from that now-PTE-mapped page > + * table. Nit: it's not a PTE-mapped page table. Maybe "... restart so we can process the PTE-mapped THP." > } > > /* Unexpected PMD-mapped THP? */ Nothing else jumped at me :) -- Cheers, David / dhildenb