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[2003:cb:c749:6600:b73a:466c:e610:686]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38a1c828bd3sm1592237f8f.10.2024.12.19.05.47.05 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 19 Dec 2024 05:47:06 -0800 (PST) Message-ID: <189f4767-e7c2-4522-b943-b644126bf897@redhat.com> Date: Thu, 19 Dec 2024 14:47:05 +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] mm: add maybe_lru_add_drain() that only drains when threshold is exceeded To: Rik van Riel , Andrew Morton Cc: "Huang, Ying" , Chris Li , Ryan Roberts , "Matthew Wilcox (Oracle)" , linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel-team@meta.com References: <20241218115604.7e56bedb@fangorn> 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: <20241218115604.7e56bedb@fangorn> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 18.12.24 17:56, Rik van Riel wrote: > The lru_add_drain() call in zap_page_range_single() always takes some locks, > and will drain the buffers even when there is only a single page pending. > > We probably don't need to do that, since we already deal fine with zap_page_range > encountering pages that are still in the buffers of other CPUs. > > On an AMD Milan CPU, will-it-scale the tlb_flush2_threads test performance with > 36 threads (one for each core) increases from 526k to 730k loops per second. > > The overhead in this case was on the lruvec locks, taking the lock to flush > a single page. There may be other spots where this variant could be appropriate. > > Signed-off-by: Rik van Riel > --- > include/linux/swap.h | 1 + > mm/memory.c | 2 +- > mm/swap.c | 18 ++++++++++++++++++ > mm/swap_state.c | 2 +- > 4 files changed, 21 insertions(+), 2 deletions(-) > > diff --git a/include/linux/swap.h b/include/linux/swap.h > index dd5ac833150d..a2f06317bd4b 100644 > --- a/include/linux/swap.h > +++ b/include/linux/swap.h > @@ -391,6 +391,7 @@ static inline void lru_cache_enable(void) > } > > extern void lru_cache_disable(void); > +extern void maybe_lru_add_drain(void); > extern void lru_add_drain(void); > extern void lru_add_drain_cpu(int cpu); > extern void lru_add_drain_cpu_zone(struct zone *zone); > diff --git a/mm/memory.c b/mm/memory.c > index 2635f7bceab5..1767c65b93ad 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -1919,7 +1919,7 @@ void zap_page_range_single(struct vm_area_struct *vma, unsigned long address, > struct mmu_notifier_range range; > struct mmu_gather tlb; > > - lru_add_drain(); > + maybe_lru_add_drain(); > mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma->vm_mm, > address, end); > hugetlb_zap_begin(vma, &range.start, &range.end); > diff --git a/mm/swap.c b/mm/swap.c > index 9caf6b017cf0..001664a652ff 100644 > --- a/mm/swap.c > +++ b/mm/swap.c > @@ -777,6 +777,24 @@ void lru_add_drain(void) > mlock_drain_local(); > } > > +static bool should_lru_add_drain(void) > +{ > + struct cpu_fbatches *fbatches = this_cpu_ptr(&cpu_fbatches); > + int pending = folio_batch_count(&fbatches->lru_add); > + pending += folio_batch_count(&fbatches->lru_deactivate); > + pending += folio_batch_count(&fbatches->lru_deactivate_file); > + pending += folio_batch_count(&fbatches->lru_lazyfree); > + > + /* Don't bother draining unless we have several pages pending. */ > + return pending > SWAP_CLUSTER_MAX; > +} > + > +void maybe_lru_add_drain(void) > +{ > + if (should_lru_add_drain()) > + lru_add_drain(); > +} > + > /* > * It's called from per-cpu workqueue context in SMP case so > * lru_add_drain_cpu and invalidate_bh_lrus_cpu should run on > diff --git a/mm/swap_state.c b/mm/swap_state.c > index 3a0cf965f32b..1ae4cd7b041e 100644 > --- a/mm/swap_state.c > +++ b/mm/swap_state.c > @@ -317,7 +317,7 @@ void free_pages_and_swap_cache(struct encoded_page **pages, int nr) > struct folio_batch folios; > unsigned int refs[PAGEVEC_SIZE]; > > - lru_add_drain(); > + maybe_lru_add_drain(); I'm wondering about the reason+effect of this existing call. Seems to date back to the beginning of git. Likely it doesn't make sense to have effectively-free pages in the LRU+mlock cache. But then, this only considers the local CPU LRU/mlock caches ... hmmm So .... do we need this at all? :) -- Cheers, David / dhildenb