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[2003:d8:2f14:2400:afc:9797:137c:a25b]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-46e1ce10bacsm40101155e9.0.2025.09.24.05.38.37 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 24 Sep 2025 05:38:39 -0700 (PDT) Message-ID: Date: Wed, 24 Sep 2025 14:38:37 +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 v2 4/4] mm: thp: reparent the split queue during memcg offline To: Qi Zheng , hannes@cmpxchg.org, hughd@google.com, mhocko@suse.com, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, lorenzo.stoakes@oracle.com, ziy@nvidia.com, harry.yoo@oracle.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, akpm@linux-foundation.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org References: <55370bda7b2df617033ac12116c1712144bb7591.1758618527.git.zhengqi.arch@bytedance.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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <55370bda7b2df617033ac12116c1712144bb7591.1758618527.git.zhengqi.arch@bytedance.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 23.09.25 11:16, Qi Zheng wrote: > In the future, we will reparent LRU folios during memcg offline to > eliminate dying memory cgroups, which requires reparenting the split queue > to its parent. > > Similar to list_lru, the split queue is relatively independent and does > not need to be reparented along with objcg and LRU folios (holding > objcg lock and lru lock). So let's apply the same mechanism as list_lru > to reparent the split queue separately when memcg is offine. > > Signed-off-by: Qi Zheng > --- > include/linux/huge_mm.h | 2 ++ > include/linux/mmzone.h | 1 + > mm/huge_memory.c | 39 +++++++++++++++++++++++++++++++++++++++ > mm/memcontrol.c | 1 + > mm/mm_init.c | 1 + > 5 files changed, 44 insertions(+) > > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h > index f327d62fc9852..a0d4b751974d2 100644 > --- a/include/linux/huge_mm.h > +++ b/include/linux/huge_mm.h > @@ -417,6 +417,7 @@ static inline int split_huge_page(struct page *page) > return split_huge_page_to_list_to_order(page, NULL, ret); > } > void deferred_split_folio(struct folio *folio, bool partially_mapped); > +void reparent_deferred_split_queue(struct mem_cgroup *memcg); > > void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, > unsigned long address, bool freeze); > @@ -611,6 +612,7 @@ static inline int try_folio_split(struct folio *folio, struct page *page, > } > > static inline void deferred_split_folio(struct folio *folio, bool partially_mapped) {} > +static inline void reparent_deferred_split_queue(struct mem_cgroup *memcg) {} > #define split_huge_pmd(__vma, __pmd, __address) \ > do { } while (0) > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > index 7fb7331c57250..f3eb81fee056a 100644 > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -1346,6 +1346,7 @@ struct deferred_split { > spinlock_t split_queue_lock; > struct list_head split_queue; > unsigned long split_queue_len; > + bool is_dying; It's a bit weird to query whether the "struct deferred_split" is dying. Shouldn't this be a memcg property? (and in particular, not exist for the pglist_data part where it might not make sense at all?). > }; > #endif > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 48b51e6230a67..de7806f759cba 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -1094,9 +1094,15 @@ static struct deferred_split *folio_split_queue_lock(struct folio *folio) > struct deferred_split *queue; > > memcg = folio_memcg(folio); > +retry: > queue = memcg ? &memcg->deferred_split_queue : > &NODE_DATA(folio_nid(folio))->deferred_split_queue; > spin_lock(&queue->split_queue_lock); > + if (unlikely(queue->is_dying == true)) { if (unlikely(queue->is_dying)) > + spin_unlock(&queue->split_queue_lock); > + memcg = parent_mem_cgroup(memcg); > + goto retry; > + } > > return queue; > } > @@ -1108,9 +1114,15 @@ folio_split_queue_lock_irqsave(struct folio *folio, unsigned long *flags) > struct deferred_split *queue; > > memcg = folio_memcg(folio); > +retry: > queue = memcg ? &memcg->deferred_split_queue : > &NODE_DATA(folio_nid(folio))->deferred_split_queue; > spin_lock_irqsave(&queue->split_queue_lock, *flags); > + if (unlikely(queue->is_dying == true)) { if (unlikely(queue->is_dying)) > + spin_unlock_irqrestore(&queue->split_queue_lock, *flags); > + memcg = parent_mem_cgroup(memcg); > + goto retry; > + } > > return queue; > } Nothing else jumped at me, but I am not a memcg expert :) -- Cheers David / dhildenb