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[2003:cb:c707:3500:5cd0:78d9:ca49:21f3]) by smtp.gmail.com with ESMTPSA id n12-20020a05600c3b8c00b00412f698af9esm5521570wms.17.2024.03.08.00.46.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 08 Mar 2024 00:46:25 -0800 (PST) Message-ID: <875a6103-9374-429b-b12b-d0dabe205031@redhat.com> Date: Fri, 8 Mar 2024 09:46:21 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/5] Remove some races around folio_test_hugetlb To: Matthew Wilcox Cc: linux-mm@kvack.org, Oscar Salvador References: <20240301214712.2853147-1-willy@infradead.org> <52599fd8-76dc-4d8f-b9f2-78146fc7a518@redhat.com> From: David Hildenbrand 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: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: xzqpo7gorkfd11eqb9r4d1oiffm6beb7 X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 917EB10001A X-Rspam-User: X-HE-Tag: 1709887589-139313 X-HE-Meta: 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 wkOmyMtL CdcLaX8wRiIEc2KfPK/b5KSiulhFJ/cbCmJUSfuDZEQ/+wkP/dwI0okBuKmi7qjowDtyokJLn77JXohcjmrYVPmisENirh505ZONz68jXPqe4sL4oeHGbCwawAQ56uZnOnEenTwyo7fBfyfLMEfdW3sRtcNQ9KXGfc9hsw7WCgA5/O/nVaw5xY+iBTQ8atr1DOySwGkXLkITqBNrVRVK2NvEUz2/LpIg66iZ7n65vzGpIDC9hks7OxLOeVhd8pg2hJd5Dt6lOz9fRb9QHfD9M6qUkgdaA6KL4Ht7TKOfviFa9jC2gMaLpgEghTs4iz8WZIQ2NWsOBWG17NHB8CAPcKubq89BsNHyDVaV/djhOCSScA0L4oX5bk/il6o5b43eK3eYSkyZLsWy+8QKgIunaDwdwSgaAsp9fScaGx6yYEYZEs96548xWXM1bS+t40oKICbCnGfBXVPsILWyzMbQfq+u4EQ== 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 08.03.24 05:31, Matthew Wilcox wrote: > On Thu, Mar 07, 2024 at 09:14:50PM +0000, Matthew Wilcox wrote: >> I suppose we could use a magic value for >> page[0].mapcount to indicate hugetlb, but that'd make page_mapcount() >> more complex. > > Actually, not significantly. I haven't tested this yet, but it should > work ... thoughts? It's certainly the simplest implementation of > folio_test_hugetlb() that we've ever had. Yes, yes, yes! So obvious and so simple! 1) In __folio_rmap_sanity_checks() we now VM_WARN_ON_ONCE we would get a hugetlb folio. 2) In folio_total_mapcount() we'll never read the subpage mapcount because folio_nr_pages_mapped() == 0. __dump_folio() might require care to just ignore the subpage mpacount as well. Maybe we can even use something like "page_has_type" to never read subpage mapcounts, and read the entire mapcount only for the exception of hugetlb folios. Apart from that, I did look at users of page_has_type(): 1) validate_page_before_insert() now correctly rejects hugetlb folios, insert_page_into_pte_locked() -> folio_add_file_rmap_pte() would nowadays properly complain about that in __folio_rmap_sanity_checks() already. 2) kpagecount_read() will always end up with pcount=0. We either special-case hugetlb folios here as well, or just let this interface bitrot and hopefully go away at some point :) Very nice! > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index f5a97dec5169..32281097f07e 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1212,6 +1212,9 @@ static inline int page_mapcount(struct page *page) > { > int mapcount = atomic_read(&page->_mapcount) + 1; > > + /* Head page repurposes mapcount; tail page leaves at -1 */ > + if (PageHeadHuge(page)) > + mapcount = 0; > if (unlikely(PageCompound(page))) > mapcount += folio_entire_mapcount(page_folio(page)); > > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h > index 735cddc13d20..6ebb573c7195 100644 > --- a/include/linux/page-flags.h > +++ b/include/linux/page-flags.h > @@ -190,7 +190,6 @@ enum pageflags { > > /* At least one page in this folio has the hwpoison flag set */ > PG_has_hwpoisoned = PG_error, > - PG_hugetlb = PG_active, > PG_large_rmappable = PG_workingset, /* anon or file-backed */ > }; > > @@ -829,29 +828,6 @@ TESTPAGEFLAG_FALSE(LargeRmappable, large_rmappable) > > #define PG_head_mask ((1UL << PG_head)) > > -#ifdef CONFIG_HUGETLB_PAGE > -int PageHuge(struct page *page); > -SETPAGEFLAG(HugeTLB, hugetlb, PF_SECOND) > -CLEARPAGEFLAG(HugeTLB, hugetlb, PF_SECOND) > - > -/** > - * folio_test_hugetlb - Determine if the folio belongs to hugetlbfs > - * @folio: The folio to test. > - * > - * Context: Any context. Caller should have a reference on the folio to > - * prevent it from being turned into a tail page. > - * Return: True for hugetlbfs folios, false for anon folios or folios > - * belonging to other filesystems. > - */ > -static inline bool folio_test_hugetlb(struct folio *folio) > -{ > - return folio_test_large(folio) && > - test_bit(PG_hugetlb, folio_flags(folio, 1)); > -} > -#else > -TESTPAGEFLAG_FALSE(Huge, hugetlb) > -#endif > - > #ifdef CONFIG_TRANSPARENT_HUGEPAGE > /* > * PageHuge() only returns true for hugetlbfs pages, but not for > @@ -907,18 +883,6 @@ PAGEFLAG_FALSE(HasHWPoisoned, has_hwpoisoned) > TESTSCFLAG_FALSE(HasHWPoisoned, has_hwpoisoned) > #endif > > -/* > - * Check if a page is currently marked HWPoisoned. Note that this check is > - * best effort only and inherently racy: there is no way to synchronize with > - * failing hardware. > - */ > -static inline bool is_page_hwpoison(struct page *page) > -{ > - if (PageHWPoison(page)) > - return true; > - return PageHuge(page) && PageHWPoison(compound_head(page)); > -} > - > /* > * For pages that are never mapped to userspace (and aren't PageSlab), > * page_type may be used. Because it is initialised to -1, we invert the > @@ -935,6 +899,7 @@ static inline bool is_page_hwpoison(struct page *page) > #define PG_offline 0x00000100 > #define PG_table 0x00000200 > #define PG_guard 0x00000400 > +#define PG_hugetlb 0x00000800 > > #define PageType(page, flag) \ > ((page->page_type & (PAGE_TYPE_BASE | flag)) == PAGE_TYPE_BASE) > @@ -1026,6 +991,37 @@ PAGE_TYPE_OPS(Table, table, pgtable) > */ > PAGE_TYPE_OPS(Guard, guard, guard) > > +#ifdef CONFIG_HUGETLB_PAGE > +PAGE_TYPE_OPS(HeadHuge, hugetlb, hugetlb) > +#else > +TESTPAGEFLAG_FALSE(HeadHuge, hugetlb) > +#endif > + > +/** > + * PageHuge - Determine if the page belongs to hugetlbfs > + * @page: The page to test. > + * > + * Context: Any context. > + * Return: True for hugetlbfs pages, false for anon pages or pages > + * belonging to other filesystems. > + */ > +static inline bool PageHuge(struct page *page) > +{ > + return folio_test_hugetlb(page_folio(page)); > +} > + > +/* > + * Check if a page is currently marked HWPoisoned. Note that this check is > + * best effort only and inherently racy: there is no way to synchronize with > + * failing hardware. > + */ > +static inline bool is_page_hwpoison(struct page *page) > +{ > + if (PageHWPoison(page)) > + return true; > + return PageHuge(page) && PageHWPoison(compound_head(page)); > +} > + > extern bool is_free_buddy_page(struct page *page); > > PAGEFLAG(Isolated, isolated, PF_ANY); > @@ -1092,7 +1088,7 @@ static __always_inline void __ClearPageAnonExclusive(struct page *page) > */ > #define PAGE_FLAGS_SECOND \ > (0xffUL /* order */ | 1UL << PG_has_hwpoisoned | \ > - 1UL << PG_hugetlb | 1UL << PG_large_rmappable) > + 1UL << PG_large_rmappable) > > #define PAGE_FLAGS_PRIVATE \ > (1UL << PG_private | 1UL << PG_private_2) > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index ed1581b670d4..23b62df21971 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -1623,7 +1623,7 @@ static inline void __clear_hugetlb_destructor(struct hstate *h, > { > lockdep_assert_held(&hugetlb_lock); > > - folio_clear_hugetlb(folio); > + __folio_clear_hugetlb(folio); > } > > /* > @@ -1710,7 +1710,7 @@ static void add_hugetlb_folio(struct hstate *h, struct folio *folio, > h->surplus_huge_pages_node[nid]++; > } > > - folio_set_hugetlb(folio); > + __folio_set_hugetlb(folio); > folio_change_private(folio, NULL); > /* > * We have to set hugetlb_vmemmap_optimized again as above > @@ -2048,7 +2048,7 @@ static void __prep_account_new_huge_page(struct hstate *h, int nid) > > static void init_new_hugetlb_folio(struct hstate *h, struct folio *folio) > { > - folio_set_hugetlb(folio); > + __folio_set_hugetlb(folio); > INIT_LIST_HEAD(&folio->lru); > hugetlb_set_folio_subpool(folio, NULL); > set_hugetlb_cgroup(folio, NULL); > @@ -2158,22 +2158,6 @@ static bool prep_compound_gigantic_folio_for_demote(struct folio *folio, > return __prep_compound_gigantic_folio(folio, order, true); > } > > -/* > - * PageHuge() only returns true for hugetlbfs pages, but not for normal or > - * transparent huge pages. See the PageTransHuge() documentation for more > - * details. > - */ > -int PageHuge(struct page *page) > -{ > - struct folio *folio; > - > - if (!PageCompound(page)) > - return 0; > - folio = page_folio(page); > - return folio_test_hugetlb(folio); > -} > -EXPORT_SYMBOL_GPL(PageHuge); > - > /* > * Find and lock address space (mapping) in write mode. > * > -- Cheers, David / dhildenb