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 AF0B5357D18 for ; Thu, 27 Aug 2026 19:33:12 +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=1787859193; cv=none; b=o3SXyKExZdNkFVkVs6auYg1lXxbAJ655cMmY2cK/bitjqGOAbZQruwcFNa1e1GybV+q328qKwGkX1Koe7VYUAMcjtIEFyv98ElReCLNKyhyJTNrOvqOwEYyRGpu7yGEyVKQY2sICTsSBFlOdcxYL03h4DqZBI4e0m5I6VYUtnoI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787859193; c=relaxed/simple; bh=tZJU6Kpcl+wbZXLBUK5aXCvg8rHjqkp5uZbiwwMNtQ4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=utlT1M+qmTILL+UelPVu+PLaEucMG6po+KjenwkXgfiqVsJcYX18xtKfltVQ7eiBa6SLeYyJsWWsfVjkh0ZF1Fc+QjzdG1UUpexOgMKGC5zwmnMyUioB8+QgYHtILhvWo/Z7ZQdJgD2Dv5fHmfvPmZa8KJAXSzxBpjbpKKvtm8Q= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=e6dTwqdt; 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="e6dTwqdt" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 64D121F000E9; Thu, 27 Aug 2026 19:33:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787859192; bh=QBxAGEwWU0H0ff3LVsxf4cSkIdLbDrdQ68KoXtPl+VA=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=e6dTwqdtGf+SyEahxsEzGjp57PZcdWa3GU4Uz7Xd9yCRQN1Fe+cZ/zUpgCul2Y23+ XyP93+n5L/BowvMUDI4/vMQcmXOGe3/ZNjAdYWOUypx7JmXVXv03QPBCDE0TeHFiwg mEdGzDn7K+cMXBMlrEeHVlgSd40tjkliSIE/D9BQu++seWSRY87lxADLmVDA2q4t5B kjvIpNKxjCF2vccxPmLA7xkOrXmP+fqhL0/UfY/Dp8sAks+c5k4Beel/zy8oKUU7Ry NQv+sgbN/DtcRwcQNEL6kNLSiilORjRruaRv8o259RHSF4XMFhXrq8Ix4O2VOBQAIk 9gO8ShXQxXjLw== Message-ID: <08115f0c-e2a4-4c65-a56d-29c751ee9360@kernel.org> Date: Thu, 27 Aug 2026 21:33:04 +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 v3 14/18] mm/huge_memory: clean up after-split folio freeing in __folio_split To: Kairui Song Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Lorenzo Stoakes , Zi Yan , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Lance Yang , Usama Arif , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Chris Li , Kemeng Shi , Nhat Pham , Baoquan He , Barry Song , Youngjun Park , Shivam Kalra References: <20260821-swap-thp-cleanup-v3-0-9b43f5163238@tencent.com> <20260821-swap-thp-cleanup-v3-14-9b43f5163238@tencent.com> <9adcaf53-3a40-4d97-9365-b9af97891894@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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 8/27/26 19:47, Kairui Song wrote: > On Fri, Aug 28, 2026 at 12:48 AM David Hildenbrand (Arm) > wrote: >> >> On 8/20/26 20:55, Kairui Song via B4 Relay wrote: >>> From: Kairui Song >>> >>> Replace free_folio_and_swap_cache() with an explicit folio_free_swap() >>> and folio_put() in the after-split loop. free_folio_and_swap_cache() >>> unlocks the folio, then free_swap_cache() must trylock it again and >>> re-check folio_mapped() before freeing the swap cache entries; if the >>> trylock loses a race, the entries are left behind even though the folio >>> reference is dropped. The sub folios are still locked and unmapped >>> here, so just directly call folio_free_swap() directly under the lock, >>> unlock and drop the reference. This makes the swap cache freeing >>> deterministic and the reference drop explicit. >>> >>> Reviewed-by: Zi Yan >>> Signed-off-by: Kairui Song >>> --- >>> mm/huge_memory.c | 10 ++++++---- >>> 1 file changed, 6 insertions(+), 4 deletions(-) >>> >>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >>> index 84c6e4bbaa88..113a33cddace 100644 >>> --- a/mm/huge_memory.c >>> +++ b/mm/huge_memory.c >>> @@ -4337,14 +4337,16 @@ static int __folio_split(struct folio *folio, unsigned int new_order, >>> if (new_folio == page_folio(lock_at)) >>> continue; >>> >>> - folio_unlock(new_folio); >>> /* >>> * Subpages whose mapping has been zapped may be freed >>> * earlier, but freeing them requires taking the >>> - * lru_lock, so we defer put_page() on tail pages until >>> + * lru_lock, so we defer folio_put() on tail pages until >>> * after the split completes. >>> */ >>> - free_folio_and_swap_cache(new_folio); >>> + if (is_swapcache && !folio_mapped(new_folio)) >>> + folio_free_swap(new_folio); >> >> But this is effectively duplicating code that belongs into swap code. >> >> Should we instead have a helper next to free_folio_and_swap_cache that consumes >> an already locked folio? > > I think the only duplication here is the is_swapcache and folio_mapped > check? folio_free_swap is a common swap helper. And putting the > folio_unlock and folio_put in the swap side looks odd to me, since the > folio is locked here and refs get here through the function's > convention. Pairing these unlock and put closer to the convention > doesn't seem too bad IMO. I was more concerned about the folio_mapped() check. Because the code now has to guess under which circumstances it makes sense to call folio_free_swap(), which is precisely what free_folio_and_swap_cache() avoided. And we already do have other code doing that, like KSM's replace_page(), and it feels like that should all be cleaned up. But no strong objection to your current code. It just looks a bit suboptimal that we have no helper that wraps the swapcache and folio_mapped() check. -- Cheers, David