From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7E0CC33121C for ; Fri, 19 Jun 2026 14:04:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781877889; cv=none; b=OBFJeo78dq7xrjAyvCaHhzB5j0zcQXje6CNtaxZ+bLdrpRqB6vd2pLzEndNW5nnzIauuIMikD1rFl1BCFyoztJA2m7d2sfm1WU+FNr4LGSKNi6Wb65IDoecC2Uj9++/sylgQtQrosi+Hmg85M8lTeAwkvwDPZ0A8JADCIOrQVQQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781877889; c=relaxed/simple; bh=Rxgk3s44Xg2v592eD4HNXB5ErTf9Nqo00ZB8Zd3HRP4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=C3ELLAwtsRun2zljG05Tx+mOB7rT7WLIQLGV0YowsmVEk3aZ1MTnxKePECwDmxzgUyf5J/3bgWovUt7sbS9YACB9CrtxHKLD4RMwq5uTFCezDxk+ayd4+zeCetEXVaXF+45FQruXHu9fHsrCRwufkwB1XovSMr6tnw4yd7Xchbo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=cZO0hMlY; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="cZO0hMlY" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A87C81F000E9; Fri, 19 Jun 2026 14:04:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781877888; bh=zcXYQhPIRFsQtxUPChITDbxpiAkS/ucijCaXlahVxJU=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=cZO0hMlYPjRn74q3/5UhL0uaKXK1oDX4WSNG8e0fBbv1apYbE+V6fIaeMVhCxQBAx 9O05eJiKDj7rOPMyRdVUJPxh+ZQofxNsSsPqe5Jfm8qdfXXX/42wxZxEHjrqGG7uQL 9SjVaGzwFeuheeZCY2vjMPB1EqpZpFj72jUnmMFdSMYJpL43WDWnqFRAVQwnlh3DKc j3SD3ih2MMHUIPhSyvtUrVePVAs8SzOMoXSAr7r1ZD3itN5MNRtVLBfHXIU4mb87Ac USD8XcwzsJE0adC3eUUvZ4a2byylWYU9L+3GUDN7p67shS/id3zd6wuQCOzQCSYL+q 2VmJy9J8pYP8g== Message-ID: <5790c4a4-d502-4180-82f5-47de5809a4fe@kernel.org> Date: Fri, 19 Jun 2026 16:04:42 +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: [RFC PATCH] mm: Avoiding split large folios if swap has no space To: "Barry Song (Xiaomi)" , akpm@linux-foundation.org, linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, Nanzhe Zhao , Lorenzo Stoakes , Zi Yan , Baolin Wang , "Liam R . Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Lance Yang , Kairui Song , Qi Zheng , Shakeel Butt , Axel Rasmussen , Yuanchu Xie , Wei Xu References: <20260618221720.71768-1-baohua@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+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: <20260618221720.71768-1-baohua@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 6/19/26 00:17, Barry Song (Xiaomi) wrote: > When swap is disabled or exhausted, swap slot allocation > may fail during swapout, causing large folios to be split > into small folios. The splitting is reasonable when we > truly fail to obtain contiguous swap slots, but it is > pointless in the no-space case. > > A simple way to reproduce this is to invoke MADV_PAGEOUT on > a system with mTHP enabled but without swap configured. > > #define SIZE (16 * 1024 * 1024) > int main(void) > { > char *buf = mmap(NULL, SIZE, PROT_READ | PROT_WRITE, > MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); > memset(buf, 1, SIZE); > madvise(buf, SIZE, MADV_PAGEOUT); > munmap(buf, SIZE); > return 0; > } > > With 16KB mTHP enabled, we observe: > ~ # cat /sys/kernel/mm/transparent_hugepage/hugepages-16kB/stats/split > 1024 > > This patch checks swap space before splitting. If there is > no available space, it skips splitting. After the patch, we > observe: > ~ # cat /sys/kernel/mm/transparent_hugepage/hugepages-16kB/stats/split > 0 > > Reported-by: Nanzhe Zhao > Cc: David Hildenbrand > Cc: Lorenzo Stoakes > Cc: Zi Yan > Cc: Baolin Wang > Cc: Liam R. Howlett > Cc: Nico Pache > Cc: Ryan Roberts > Cc: Dev Jain > Cc: Lance Yang > Cc: Kairui Song > Cc: Qi Zheng > Cc: Shakeel Butt > Cc: Axel Rasmussen > Cc: Yuanchu Xie > Cc: Wei Xu > Signed-off-by: Barry Song (Xiaomi) > --- > mm/vmscan.c | 15 +++++++++++++-- > 1 file changed, 13 insertions(+), 2 deletions(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 299b5d9e8836..33f84a5fe7ee 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -339,8 +339,7 @@ static bool can_demote(int nid, struct scan_control *sc, > return !nodes_empty(allowed_mask); > } > > -static inline bool can_reclaim_anon_pages(struct mem_cgroup *memcg, > - int nid, > +static inline bool __can_reclaim_anon_pages(struct mem_cgroup *memcg, > struct scan_control *sc) > { > if (memcg == NULL) { > @@ -356,6 +355,16 @@ static inline bool can_reclaim_anon_pages(struct mem_cgroup *memcg, > return true; > } > > + return false; > +} > + > +static inline bool can_reclaim_anon_pages(struct mem_cgroup *memcg, > + int nid, > + struct scan_control *sc) > +{ > + if (__can_reclaim_anon_pages(memcg, sc)) > + return true; > + > /* > * The page can not be swapped. > * > @@ -1280,6 +1289,8 @@ static unsigned int shrink_folio_list(struct list_head *folio_list, > > if (!folio_test_large(folio)) > goto activate_locked_split; > + if (!__can_reclaim_anon_pages(memcg, sc)) > + goto activate_locked_split; Why are we even trying to allocate swap space if we cannot reclaim such pages? Makes we wonder whether we would want to have that check earlier, before the folio_alloc_swap(). Any downsides? -- Cheers, David