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b=KKMlr2HhPM/D8nBnfTQQbkU0LpZdhdAigkpZSKCzB4j5WYFyuE+D1kBdSevS7KLKBaLpte3Nx0dKY0IM9XXXyWNBUpCJXNZ0/Nlos/SzgQLXc2TkCgV2KmT+kJCqgGmlrVv7sIflT8oZCFMOExUa97Ltas6VB6H3sy1lePU8pPE= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R181e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam011083073210;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=16;SR=0;TI=SMTPD_---0X8rG74f_1786529828; Received: from 30.74.144.118(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0X8rG74f_1786529828 cluster:ay36) by smtp.aliyun-inc.com; Wed, 12 Aug 2026 18:17:09 +0800 Message-ID: Date: Wed, 12 Aug 2026 18:17:08 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/mglru: Fix young counter undercount for large folios To: Hui Zhu , Andrew Morton , Johannes Weiner , David Hildenbrand , Michal Hocko , Qi Zheng , Shakeel Butt , Lorenzo Stoakes , Kairui Song , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Hui Zhu References: <20260812065933.103627-1-hui.zhu@linux.dev> From: Baolin Wang In-Reply-To: <20260812065933.103627-1-hui.zhu@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: DF255140007 X-Rspam-User: X-Stat-Signature: hcpuyxrp4ndodmadcts4xbqdeafmqpyg X-Rspamd-Server: rspam06 X-HE-Tag: 1786529835-633258 X-HE-Meta: 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 v9/GEsxl 5jwqMOiPgHyzmnB2FQ/HyNeRE8wHunrGkoXcJwZ/1/h+LX/sJdLPaBJh7O7kJOQwRf7sbiLYmRQo0a6i8TM8xRdpUIw2eLfo6ZJspxW6V+pgKlqW2d/xYz6z3tLz368XHKdAt07s8wR2a7UIXn7/2HTKL/URC+RCyYNC+9tTLtQ3/AN+9YilaLEoqus5fBWNClLE4qkjk1OaHvgSzxzAnzaQAB7DQjsDtRtZwkxRTA10d+qi7fM4SyFvBK3k++fN0qHqF6K5yFp5jnND09mAOfAwKHKwHQLB41/fZQVPMZHJxlqM= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/12/26 2:59 PM, Hui Zhu wrote: > From: Hui Zhu > > In lru_gen_look_around(), the young counter tracks the number of young > PTEs. The original folio's contribution is represented by the initial > value of young: test_and_clear_young_ptes_notify() is called on it at > function entry, and the function returns early if it is not young. In > the subsequent loop, the original folio is skipped (its accessed bits > were already cleared), so it is not double-counted. > > However, young is initialized to 1 regardless of the folio size. When > the original folio is a large folio with nr PTEs, its young count is > underestimated by nr - 1. This inconsistency can cause > suitable_to_scan() to return false, preventing the PMD from being added > to the bloom filter and reducing aging accuracy for mTHP workloads. > > Initialize young to nr so the original folio is accounted the same way > as other young folios in the loop (young += nr). > > Signed-off-by: Hui Zhu > --- Good catch. Please also add the Fixes tag: Fixes: 56e5b60b2114 ("mm: support batched checking of the young flag for MGLRU") With that, Reviewed-by: Baolin Wang > mm/vmscan.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index bc324e37c5f1..264017850a55 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -4192,7 +4192,7 @@ bool lru_gen_look_around(struct page_vma_mapped_walk *pvmw, unsigned int nr) > unsigned long end; > struct lru_gen_mm_walk *walk; > struct folio *last = NULL; > - int young = 1; > + int young = nr; > pte_t *pte = pvmw->pte; > unsigned long addr = pvmw->address; > struct vm_area_struct *vma = pvmw->vma;