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[2003:cb:c719:5b00:61af:900f:3aef:3af3]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4247d0ca68esm17846255e9.30.2024.06.20.01.49.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 20 Jun 2024 01:49:47 -0700 (PDT) Message-ID: <60a075da-7c7e-4d99-ac52-059e5a17b72e@redhat.com> Date: Thu, 20 Jun 2024 10:49:46 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/3] mm: use folio_add_new_anon_rmap() if folio_test_anon(folio)==false To: Barry Song <21cnbao@gmail.com> Cc: akpm@linux-foundation.org, linux-mm@kvack.org, baolin.wang@linux.alibaba.com, chrisl@kernel.org, linux-kernel@vger.kernel.org, mhocko@suse.com, ryan.roberts@arm.com, shy828301@gmail.com, surenb@google.com, v-songbaohua@oppo.com, willy@infradead.org, ying.huang@intel.com, yosryahmed@google.com, yuzhao@google.com, Shuai Yuan References: <20240617231137.80726-1-21cnbao@gmail.com> <20240617231137.80726-3-21cnbao@gmail.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 6EEBA100003 X-Stat-Signature: kt91dqtcnaoquyjhopiykrxo947kypwi X-Rspam-User: X-HE-Tag: 1718873394-529248 X-HE-Meta: U2FsdGVkX194XGz/S70TN3pb8gBX8aSymYtkywoLFy2j3ES2KG8sfGQggEhOjEizzhup2FOFI+7sdChiJsl/ikeSC5cg04axPIYEZ/juv/w+y/GYzS2mn4BZvixEvZ/9XAsK9XuECtoNRwj0TRr588Hnwgr9AYLRhOKIipN25MPnKljEP14tmxuuMe2Y2DSadBdpwTct8Wj+elzTS428RBHV7xvKBwERfBGyn/LT9LdNRsizS70OOV1XCFuSv3YNCq4jzWdgQMK8z7KJf64wSOjquCEqEcfpCgldnWStFM11L4poWxfCoewm1FPGQeLP1klA91hxgYzOdkrdp2xRMBU2/yzpCR5u7pOTqapixNMJqkFrOhsTuEC0wBvEuNHdNwkTpsSWGcTRAkHd8Uuo8MLzOZW0wZru49VvIZG7hSJ+Ij29e0q2AHR+3BRWSoQoJJ3lS9iMlhEKYXcC2YRuhn3qs3ZbrXNQvCoWGVqTHMybCe2Kw2sMOAjI9o/H+y2nSsMRUXGvSyFOPDn9XowuWTq1lhal13irg4nkrESk5S9rgbeFeFvOHetpD2zA48dI268O7S1+BrVdDOj4smlFKffpRLhNMkmk4OYHyIULOmpMKE7BNMyUlf8XhdvT9sEamndsFzSQFDDsl1XcwqLQHEAuNHe40Gn9eq/cwcaj8B4QxKZtaL5NHjHZfQSNseTlbNIdo9EyTNdMxI2eX0+tEiJPlEvsgpBbSaDKj0ebwR+5t98i17i31jTJcRVtAEjE2JcGhaZx5Cr/4DffrYD3zDk2U7SZXdYwhRUaQF4PTIkupZghXkHK1CliOXsauZnD6Xk5SNF8UtfVA5CVmFR0TeGe2HFVCi2MjoG3HehAQ0afar6MbnFHw+KWNR09sPoo9FARDmf2SkGnXct6b/089sVIBussFHiiBefc9PojvxGZaDRzUoHbereZ+opFwWgcCBVbCURzmoGzAVphGJq mo/T0hHg 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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 20.06.24 10:33, Barry Song wrote: > On Thu, Jun 20, 2024 at 7:46 PM David Hildenbrand wrote: >> >> On 18.06.24 01:11, Barry Song wrote: >>> From: Barry Song >>> >>> For the !folio_test_anon(folio) case, we can now invoke folio_add_new_anon_rmap() >>> with the rmap flags set to either EXCLUSIVE or non-EXCLUSIVE. This action will >>> suppress the VM_WARN_ON_FOLIO check within __folio_add_anon_rmap() while initiating >>> the process of bringing up mTHP swapin. >>> >>> static __always_inline void __folio_add_anon_rmap(struct folio *folio, >>> struct page *page, int nr_pages, struct vm_area_struct *vma, >>> unsigned long address, rmap_t flags, enum rmap_level level) >>> { >>> ... >>> if (unlikely(!folio_test_anon(folio))) { >>> VM_WARN_ON_FOLIO(folio_test_large(folio) && >>> level != RMAP_LEVEL_PMD, folio); >>> } >>> ... >>> } >>> >>> It also improves the code’s readability. Currently, all new anonymous >>> folios calling folio_add_anon_rmap_ptes() are order-0. This ensures >>> that new folios cannot be partially exclusive; they are either entirely >>> exclusive or entirely shared. >>> >>> Suggested-by: David Hildenbrand >>> Signed-off-by: Barry Song >>> Tested-by: Shuai Yuan >>> --- >>> mm/memory.c | 8 ++++++++ >>> mm/swapfile.c | 13 +++++++++++-- >>> 2 files changed, 19 insertions(+), 2 deletions(-) >>> >>> diff --git a/mm/memory.c b/mm/memory.c >>> index 1f24ecdafe05..620654c13b2f 100644 >>> --- a/mm/memory.c >>> +++ b/mm/memory.c >>> @@ -4339,6 +4339,14 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) >>> if (unlikely(folio != swapcache && swapcache)) { >>> folio_add_new_anon_rmap(folio, vma, address, RMAP_EXCLUSIVE); >>> folio_add_lru_vma(folio, vma); >>> + } else if (!folio_test_anon(folio)) { >>> + /* >>> + * We currently only expect small !anon folios, for which we now >>> + * that they are either fully exclusive or fully shared. If we >>> + * ever get large folios here, we have to be careful. >>> + */ >>> + VM_WARN_ON_ONCE(folio_test_large(folio)); >>> + folio_add_new_anon_rmap(folio, vma, address, rmap_flags); >>> } else { >>> folio_add_anon_rmap_ptes(folio, page, nr_pages, vma, address, >>> rmap_flags); >>> diff --git a/mm/swapfile.c b/mm/swapfile.c >>> index ae1d2700f6a3..69efa1a57087 100644 >>> --- a/mm/swapfile.c >>> +++ b/mm/swapfile.c >>> @@ -1908,8 +1908,17 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd, >>> VM_BUG_ON_FOLIO(folio_test_writeback(folio), folio); >>> if (pte_swp_exclusive(old_pte)) >>> rmap_flags |= RMAP_EXCLUSIVE; >>> - >>> - folio_add_anon_rmap_pte(folio, page, vma, addr, rmap_flags); >>> + /* >>> + * We currently only expect small !anon folios, for which we now that >>> + * they are either fully exclusive or fully shared. If we ever get >>> + * large folios here, we have to be careful. >>> + */ >>> + if (!folio_test_anon(folio)) { >>> + VM_WARN_ON_ONCE(folio_test_large(folio)); >> >> (comment applies to both cases) >> >> Thinking about Hugh's comment, we should likely add here: >> >> VM_WARN_ON_FOLIO(!folio_test_locked(folio), folio); >> >> [the check we are removing from __folio_add_anon_rmap()] >> >> and document for folio_add_new_anon_rmap() in patch #1, that when >> dealing with folios that might be mapped concurrently by others, the >> folio lock must be held. > > I assume you mean something like the following for patch#1? > > diff --git a/mm/rmap.c b/mm/rmap.c > index df1a43295c85..20986b25f1b2 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -1394,7 +1394,8 @@ void folio_add_anon_rmap_pmd(struct folio > *folio, struct page *page, > * > * Like folio_add_anon_rmap_*() but must only be called on *new* folios. > * This means the inc-and-test can be bypassed. > - * The folio does not have to be locked. > + * The folio doesn't necessarily need to be locked while it's > exclusive unless two threads > + * map it concurrently. However, the folio must be locked if it's shared. > * > * If the folio is pmd-mappable, it is accounted as a THP. > */ > @@ -1406,6 +1407,7 @@ void folio_add_new_anon_rmap(struct folio > *folio, struct vm_area_struct *vma, > int nr_pmdmapped = 0; > > VM_WARN_ON_FOLIO(folio_test_hugetlb(folio), folio); > + VM_WARN_ON_FOLIO(!exclusive && !folio_test_locked(folio), folio); For now this would likely do. I was concerned about a concurrent scenario in the exclusive case, but that shouldn't really happen I guess. -- Cheers, David / dhildenb