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 D1C0A239E7E for ; Wed, 17 Jun 2026 12:47:41 +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=1781700462; cv=none; b=aF9UqEivq7XSYRyxZ9kwOD8/xMj0sl0jjjR53WyZS23iQTEPYtNr3PEcXA2HXDGjSOj8vxk7U2QKzcSeP0TpZeQ6EBi3Qpeo5mlJsNe2EfKXrfikjrUbCWkJFR2alxgefcGbTFdYOEzsDoKnXIzkuIJcX1T3UVhZ93f73q7lqYg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781700462; c=relaxed/simple; bh=VeNt8D4k0+WY+HGNt5I4ZcpMzL4TQLCI8tsq5u4lFiQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=UVE/H0o7EoYlhIT92ly1E82+AkF5NywyTtZ7Pc4lbSHVijQYz56POwbNx3UO7E004HdxYkr6sWyUQG4VY2tAE78heZ8nDvTEq0v6BaF7HdGAGD7AZuVqj/meBJ5Dlr2cy7MwrlbwBO7BbcJD0Hx0FvAcJc3A9FJGOR7VRl67GDc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=G9akpU4D; 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="G9akpU4D" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 169041F00A3A; Wed, 17 Jun 2026 12:47:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781700461; bh=vNxoXi2Xs2Z/S6rhk+D/+FM4hX0Vdz/T8a58ZEMk0Bc=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=G9akpU4D7eBc6wCgUNqt8IAwOznRQPfrvsitOvDpn9ghIDmykuLJXuAZRiZzYIrqN ZrZwtORd3cPZZtHWJCCH9EGppeiIqORFpXs/+TqJiAjTVno0KCVoiOy1rfB1TMnntU 8ojqYvzZ+R4GL/j1UulOO6DEidtfjhwPo5ffDlJc+a5auvCs6pKQ6wUsyimWCHhmbt 99OxpUwNlADvzN6r0OiK5uK9jmv6zIv6gCkmlMX0VMtQ17DxkUNKO+cmumDy1qTDXG LPjxgi75NAndePaWbiW8IeHslgbk/YCG9qUAvFuDsx8YIulPPV3H8/hXAa8xZd1xBd 2xW6WsYvkeCTQ== Message-ID: <0ea1abc4-ff2c-4070-8bfa-67f6892aaca7@kernel.org> Date: Wed, 17 Jun 2026 14:47:36 +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 v4 5/5] mm/vmscan: flush TLB for every 31 folios evictions To: Zhang Peng , Andrew Morton , Lorenzo Stoakes , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Johannes Weiner , Shakeel Butt , Axel Rasmussen , Yuanchu Xie , Wei Xu , Michal Hocko , "Liam R. Howlett" , Qi Zheng Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Barry Song , Kairui Song , Zhang Peng References: <20260525-batch-tlb-flush-v4-0-83789d6abc00@icloud.com> <20260525-batch-tlb-flush-v4-5-83789d6abc00@icloud.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: <20260525-batch-tlb-flush-v4-5-83789d6abc00@icloud.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 5/25/26 16:57, Zhang Peng wrote: > Currently we flush TLB for every dirty folio, which is a bottleneck for > systems with many cores as this causes heavy IPI usage. > > So instead, batch the folios, and flush once for every 31 folios (one > folio_batch). These folios will be held in a folio_batch releasing their > lock, then when folio_batch is full, do following steps: > > - For each folio: lock - check still evictable (writeback, mapped, > dma_pinned) > - If no longer evictable, put back to LRU > - Flush TLB once for the batch > - Pageout the folios > > Signed-off-by: Zhang Peng > --- > mm/vmscan.c | 79 ++++++++++++++++++++++++++++++++++++++++++++++++++++++------- > 1 file changed, 71 insertions(+), 8 deletions(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index abf3a2878456..c0d22afe67a5 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -1221,6 +1221,57 @@ static bool pageout_one(struct folio *folio, > return false; > } > > +static void pageout_batch(struct folio_batch *fbatch, > + struct list_head *ret_folios, > + struct folio_batch *free_folios, > + struct scan_control *sc, struct reclaim_stat *stat, > + struct swap_iocb **plug, struct list_head *folio_list, > + unsigned int *nr_reclaimed) Two tabs. But this is starting to look a bit messy. Could a helper struct be used to reduce the parameter count to something readable? > +{ > + int i, count = folio_batch_count(fbatch); > + struct folio *folio; > + > + /* > + * Reuse fbatch in-place: reinit only clears the count, the > + * underlying folios array is still accessible via saved count. > + * Filter and re-add valid folios back into the same batch. > + */ > + folio_batch_reinit(fbatch); That looks rather hacky. You reinit the batch to then traverse the batch? There must be a cleaner way. Walking and modifying the same folio batch in one go is rather crazy. > + for (i = 0; i < count; ++i) { > + folio = fbatch->folios[i]; > + if (!folio_trylock(folio)) { > + list_add(&folio->lru, ret_folios); > + continue; > + } > + > + VM_WARN_ON_FOLIO(folio_test_lru(folio), folio); > + > + if (folio_test_writeback(folio) || folio_mapped(folio) || > + folio_maybe_dma_pinned(folio)) { Took me a second to understand why exactly you test for these properties. Can you add a comment how these check here mimic what we checked earlier, before dopping the lock? > + folio_unlock(folio); > + list_add(&folio->lru, ret_folios); > + continue; > + } So, IIUC, what could have happened after dropping the folio lock is that someone would have remapped the folio to user space? Either from the pagecache or from the swap PTE -> swapcache. >From there, it could have gotten pinned through the page tables. Is that correct? What would happen if page migration finds the folio, locks it and wants to migrate it? -- Cheers, David