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 AA1343BB670; Thu, 30 Jul 2026 10:21:54 +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=1785406916; cv=none; b=PE2YoT4/Lx1BZhkSwvE8GyHxcLtpCZm/+VLhRnuQS9M6hT+cfUx4ol9pNA4VHM9eI21HBiefbbV+vgpEY1EnMKjboIJyJBUHmxJzopfd9l6FwKSX4k7C5t3uFQN/5IAq0NFU4y9xqsP6EPIi9Sw28fWPXb92MvP3CIcGrwXoDvA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785406916; c=relaxed/simple; bh=6JpsF4h2EQxj7OkvP4IBJ6Jaa7t2xceroMXUq6a/o70=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=TuRpdwTTt76/47G2eiHeGA5nfQQJ5zOBAfiAsvd+OcBfE3+LeSM2Ns038gcGOBvBHgPgNb1N/F8JWLb2zxPeXq0Kwio6NePcZjfhKaBgNC2q83n1duPHYNxFwW9JRvzhjYd7I0s0iaU7RYccaZ/CBr1EO66gQdvvimblAC9UGHE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=fpe6HTdY; 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="fpe6HTdY" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 86FF51F000E9; Thu, 30 Jul 2026 10:21:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785406914; bh=TGmEmde7MD/lWIzX2wq97sKKbT26z6cGRrn8j8z5Oh8=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=fpe6HTdYFr0KeH+LhNV7pIBaW3RmGyopHxQrgNpLi/PSI2EixHLupP7jGPJHl04UW ETbOOYJ+adlumdUmUpDzRFOBoal/1hSg0Xq+yTO3VZ8EnTAQJzMKNoW0R3X8T52yxQ WLOI2oTtjiqLMJIeo6X0vkYxXQXaN/kELQHa1Ln0/mgYuDde120JPWOURohCnLKY7q XEmqMj/jlW4hue6EQdjSr/RnM5b51pLtf+ICpqKumAfdMu6MJMEphysXr1txy2o7aG ZzDTDzhP+a/vbrBXhmxH4fi6zJvFgFwfSip09n6+eEpUkY8wuVrubJaUvyzyyLnIY1 Ybr0wSkk8bjXA== Message-ID: <4460e252-b6de-4df3-bea8-0368a9d0f4ff@kernel.org> Date: Thu, 30 Jul 2026 12:21:36 +0200 Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v9 14/41] mm: swap: Introduce lru_add_drain_progressive() To: ackerleytng@google.com, aik@amd.com, andrew.jones@linux.dev, binbin.wu@linux.intel.com, brauner@kernel.org, chao.p.peng@linux.intel.com, jmattson@google.com, jthoughton@google.com, michael.roth@amd.com, oupton@kernel.org, pankaj.gupta@amd.com, qperret@google.com, rick.p.edgecombe@intel.com, rientjes@google.com, shivankg@amd.com, steven.price@arm.com, tabba@google.com, willy@infradead.org, wyihan@google.com, yan.y.zhao@intel.com, forkloop@google.com, pratyush@kernel.org, suzuki.poulose@arm.com, aneesh.kumar@kernel.org, liam@infradead.org, Paolo Bonzini , Sean Christopherson , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Jonathan Corbet , Shuah Khan , Shuah Khan , Vishal Annapurve , Andrew Morton , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Youngjun Park , Qi Zheng , Shakeel Butt , Kiryl Shutsemau , Baoquan He , Jason Gunthorpe , John Hubbard , Peter Xu , Vlastimil Babka , "hughd@google.com" Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, linux-coco@lists.linux.dev References: <20260728-gmem-inplace-conversion-v9-0-35f9aec2aed2@google.com> <20260728-gmem-inplace-conversion-v9-14-35f9aec2aed2@google.com> 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: <20260728-gmem-inplace-conversion-v9-14-35f9aec2aed2@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/29/26 02:35, Ackerley Tng via B4 Relay wrote: > From: Ackerley Tng > > Extract the progressive LRU drain retry logic from > collect_longterm_unpinnable_folios() into a reusable helper, > lru_add_drain_progressive(). > > When attempting to isolate folios that may still reside in per-CPU folio > batches, draining is escalated progressively: > > 1. State 0: Call lru_add_drain() to flush local CPU batches. > 2. State 1: Call lru_add_drain_all() to flush all CPU batches. > 3. State >= 2: Return false to stop retrying. > > Refactor collect_longterm_unpinnable_folios() to use this new helper. > > The helper will be used by KVM's guest_memfd in a later patch. > > Signed-off-by: Ackerley Tng > --- > include/linux/swap.h | 2 ++ > mm/gup.c | 19 ++++++------------- > mm/swap.c | 15 +++++++++++++++ > 3 files changed, 23 insertions(+), 13 deletions(-) > > diff --git a/include/linux/swap.h b/include/linux/swap.h > index 8f0f68e245baa..cd54f73f34f39 100644 > --- a/include/linux/swap.h > +++ b/include/linux/swap.h > @@ -344,6 +344,8 @@ extern void lru_add_drain(void); > extern void lru_add_drain_cpu(int cpu); > extern void lru_add_drain_cpu_zone(struct zone *zone); > extern void lru_add_drain_all(void); > +bool lru_add_drain_progressive(int *drain_state); > + > void folio_deactivate(struct folio *folio); > void folio_mark_lazyfree(struct folio *folio); > extern void swap_setup(void); > diff --git a/mm/gup.c b/mm/gup.c > index 0692119b79043..5f00435e2c635 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -2268,7 +2268,7 @@ static unsigned long collect_longterm_unpinnable_folios( > { > unsigned long collected = 0; > struct folio *folio; > - int drained = 0; > + int drain_state = 0; > long i = 0; > > for (folio = pofs_get_folio(pofs, i); folio; > @@ -2287,18 +2287,11 @@ static unsigned long collect_longterm_unpinnable_folios( > continue; > } > > - if (drained == 0 && folio_may_be_lru_cached(folio) && > - folio_ref_count(folio) != > - folio_expected_ref_count(folio) + 1) { > - lru_add_drain(); > - drained = 1; > - } > - if (drained == 1 && folio_may_be_lru_cached(folio) && > - folio_ref_count(folio) != > - folio_expected_ref_count(folio) + 1) { > - lru_add_drain_all(); > - drained = 2; > - } > + while (folio_may_be_lru_cached(folio) && > + folio_ref_count(folio) != > + folio_expected_ref_count(folio) + 1 && > + lru_add_drain_progressive(&drain_state)) > + ; That's rather nasty. I was hoping that we could embed more logic in a helper. The history [1] of the refcount check is rather sad: https://lore.kernel.org/all/c5bac539-fd8a-4db7-c21c-cd3e457eee91@google.com/ ... primarily because of mlock() handling. For guest_memfd(), would mlock() ever apply on a path where you need that check? Conceptually, I wonder whether we can do the following, and rely on the refcount check only on the mlock path. >From ae30f7594692b0c47b44922c26b6480dd9584872 Mon Sep 17 00:00:00 2001 From: "David Hildenbrand (Arm)" Date: Thu, 30 Jul 2026 12:20:14 +0200 Subject: [PATCH] tmp Signed-off-by: David Hildenbrand (Arm) --- mm/gup.c | 66 ++++++++++++++++++++++++++++++++++++++++++++------------ 1 file changed, 52 insertions(+), 14 deletions(-) diff --git a/mm/gup.c b/mm/gup.c index 99902c15703b0..ec43071bd035a 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -2259,6 +2259,56 @@ static struct folio *pofs_next_folio(struct folio *folio, return pofs_get_folio(pofs, i); } +enum lru_cache_drained { + LRU_CACHE_NOT_DRAINED, + LRU_CACHE_DRAINED, + LRU_CACHE_DRAINED_ALL, +}; + +static inline void folio_likely_lru_cached(const struct folio *folio) +{ + if (!folio_may_be_lru_cached(folio)) + return false; + /* + * Having the LRU flag clear either indicates LRU cache references + * or LRU isolation. + */ + if (!folio_test_lru(folio)) + return true; + /* + * For mlocked folios, we don't have a real indication: we can only + * take a guess based on the refcount. + */ + if (!folio_test_mlock(folio)) + return false; + return folio_expected_ref_count(folio) == folio_ref_count(folio) = 1; +} + +/** + * lru_cache_drain_for_folio() - progressively try draining the lru cache + * @folio: The folio. + * @drained: Status initialized to LRU_CACHE_NOT_DRAINED by the caller. + * + * TODO + */ +static void lru_cache_drain_for_folio(const struct folio *folio, + enum lru_cache_drained *drained) +{ + if (!folio_likely_lru_cached(folio)) + return false; + + /* Try local draining first, if not already done previously. */ + if (*drained == LRU_CACHE_NOT_DRAINED) { + lru_add_drain(); + *drained = LRU_CACHE_DRAINED; + } + /* Try draining all CPUs next if still not an LRU folio. */ + if (folio_likely_lru_cached(folio) && *drained == LRU_CACHE_DRAINED) { + lru_add_drain_all(); + *drained = LRU_CACHE_DRAINED_ALL; + } +} + /* * Returns the number of collected folios. Return value is always >= 0. */ @@ -2266,9 +2316,9 @@ static unsigned long collect_longterm_unpinnable_folios( struct list_head *movable_folio_list, struct pages_or_folios *pofs) { + enum lru_cache_drained drained = LRU_CACHE_NOT_DRAINED; unsigned long collected = 0; struct folio *folio; - int drained = 0; long i = 0; for (folio = pofs_get_folio(pofs, i); folio; @@ -2287,19 +2337,7 @@ static unsigned long collect_longterm_unpinnable_folios( continue; } - if (drained == 0 && folio_may_be_lru_cached(folio) && - folio_ref_count(folio) != - folio_expected_ref_count(folio) + 1) { - lru_add_drain(); - drained = 1; - } - if (drained == 1 && folio_may_be_lru_cached(folio) && - folio_ref_count(folio) != - folio_expected_ref_count(folio) + 1) { - lru_add_drain_all(); - drained = 2; - } - + lru_cache_drain_for_folio(folio, &drained); if (!folio_isolate_lru(folio)) continue; -- 2.43.0 -- Cheers, David