From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 96CEBCDB46B for ; Mon, 22 Jun 2026 08:58:30 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 833326B008A; Mon, 22 Jun 2026 04:58:29 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 7E4696B008C; Mon, 22 Jun 2026 04:58:29 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6ADFA6B0092; Mon, 22 Jun 2026 04:58:29 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 410FC6B008A for ; Mon, 22 Jun 2026 04:58:29 -0400 (EDT) Received: from smtpin08.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay07.hostedemail.com (Postfix) with ESMTP id AC9D3166CCD for ; Mon, 22 Jun 2026 08:58:28 +0000 (UTC) X-FDA: 84906947496.08.78F18A8 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf30.hostedemail.com (Postfix) with ESMTP id E84C380009 for ; Mon, 22 Jun 2026 08:58:26 +0000 (UTC) Authentication-Results: imf30.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=Qg7LegUu; spf=pass (imf30.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1782118707; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=1axEUDSKUCZxXWYIuAFylYrZQLRQGoLVwSR5dVqSN1g=; b=S4i4QW5xmQ+7nKpU54lEROXAHnzMPYXBVhTsA0mBGRfp+95tHvkssrPscbqym/Zpjj1ub8 IF9flqTsV4UWjGfNKKtsHSAwa3dPfiVAFhSO47hBPoNpircqykOXizK/rcpM/2Cs4ClfzV tDOpCVdRw9TJ3l47VYYhM/25iSUBCUM= ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1782118707; b=fsXBNGlsjZgfE8wtWmsQrw0axcsOtddM25wlPx98qyd1Q3QRTdMCtfb4emrbKTfeGT7HMK kEwD5Vfn8ggDCquq4sQhYLiVMHDQClmpQCrKUZH88MOEKI3qFnd39bzQxFQgIhZwWHaHjq JAjo9xtsJU0eims7mGoUFGLyeNAsswE= ARC-Authentication-Results: i=1; imf30.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=Qg7LegUu; spf=pass (imf30.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id F335A41A51; Mon, 22 Jun 2026 08:58:25 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6A7651F00A3D; Mon, 22 Jun 2026 08:58:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782118705; bh=1axEUDSKUCZxXWYIuAFylYrZQLRQGoLVwSR5dVqSN1g=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Qg7LegUu+eE/t5ZVmf123u++iukFhC3v6Y0SR+Zf/z+Gf8dQvLeMP5Yl15J54JXtF 7CuCD7p5Ohy5AQkm9SZZ8ckeqHHMoV6i+3QD4yNCt+aUJMIdQNOfhNVvXITkMLOibq gBkVFCqpLX9EY/Y1dEITKk299MSqD9fs7K8bC/NesR/jHSan4dlhCKvvjnEoffOLnY SknsBq0f10PADghliYZdWWlMT0M3hANV3uILg3NpJ3g3uXimncVYJ1L+FR9DA5XAo7 1jqFRXVGUp04GilEjCFB4/2tJz1lpmlJ8+m/BS8yUmw+SCuMaKmC4yv7kMrQnkQlMp GhGViHi6ddDmQ== Message-ID: <4aa8350e-712f-4380-b3bf-2ff06cf2a35d@kernel.org> Date: Mon, 22 Jun 2026 10:58:20 +0200 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)" Cc: akpm@linux-foundation.org, axelrasmussen@google.com, baolin.wang@linux.alibaba.com, dev.jain@arm.com, kasong@tencent.com, lance.yang@linux.dev, liam@infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, ljs@kernel.org, npache@redhat.com, qi.zheng@linux.dev, ryan.roberts@arm.com, shakeel.butt@linux.dev, weixugc@google.com, yuanchu@google.com, zhaonanzhe@xiaomi.com, ziy@nvidia.com References: <5790c4a4-d502-4180-82f5-47de5809a4fe@kernel.org> <20260620081017.89085-1-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: <20260620081017.89085-1-baohua@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Stat-Signature: st641yoz4mjydbkg97xd8wymhtby5ur7 X-Rspamd-Queue-Id: E84C380009 X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1782118706-836901 X-HE-Meta: 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 /Lulc9D6 IIuBgH6n3BNks38xyU2e0dKSmlagUE1eSCM4vht5VTcafOZcuSXY1JAqlmTfg6Hc13fLm2VWXxCiPYw7Gng5Yv2Q+rL4TGk7IVAkkZA6UrbZxlYD2gzQODel2hXg/2N37kGeWljl2wnR8BZ3CBoGWzcBSCggfjuv3pIbUaHQko1PNet8+vxF4GLxs2aGb7izd6uD/zFRUOagjF7bNdVLH4nF/bNWQmornZb9GEwHdX1ueZlPVL29IioAAchWF3B+lGK0Cd6gq+L0RFoj3nPMIzt5slHM5u5qpUZPnNaRddqtZ/U0f9VIqu9Sdag== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/20/26 10:10, Barry Song (Xiaomi) wrote: > On Fri, Jun 19, 2026 at 10:04 PM David Hildenbrand (Arm) wrote: > [...] >>> /* >>> * 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? > > I don't think there are any obvious downsides there. One issue is that > the memcg may not be passed from reclaim_pages(), so memcg would > always be NULL. However, the folio could still belong to a memcg > whose swap quota has been exhausted. In that case, my > __can_reclaim_anon_pages() will fail when checking whether we can > swap out. But switching to folio_memcg() also seems awkward. > > So I feel Kairui’s suggestion [1] might be the best approach. In > folio_alloc_swap(), we return -EAGAIN to tell vmscan.c that > we can split the folio and retry the swap-out. > only when there are sufficient swap slots and sufficient memcg swap > quota do we return -EAGAIN, allowing vmscan to perform a split. > > diff --git a/mm/swapfile.c b/mm/swapfile.c > index 78b49b0658ad..62e2c506ccae 100644 > --- a/mm/swapfile.c > +++ b/mm/swapfile.c > @@ -1755,6 +1755,9 @@ int folio_alloc_swap(struct folio *folio) > VM_WARN_ON_ONCE(1); > return -EINVAL; > } > + > + if (get_nr_swap_pages() < (1 << order)) > + return -ENOMEM; I guess we could be clearer with the return value: -> !get_nr_swap_pages() -> -ENOSPC / -ENOMEM (no space at all) -> get_nr_swap_pages() < (1 << order) -> -E2BIG (there is some space, but not for the full thing) But now I wonder whether we would also want to check "is there any free swap space", not just "is there any swap". Essentially, try returning -E2BIG if there is the chance to swap out after split, and -ENOSPC / -ENOMEM if a split wouldn't help. > } > > again: > @@ -1769,11 +1772,13 @@ int folio_alloc_swap(struct folio *folio) > } > > /* Need to call this even if allocation failed, for MEMCG_SWAP_FAIL. */ > - if (unlikely(mem_cgroup_try_charge_swap(folio))) > + if (unlikely(mem_cgroup_try_charge_swap(folio))) { > swap_cache_del_folio(folio); > + return -ENOMEM; Here we wouldn't have the information whether we could charge after a split. So that would require a rework to signal this more cleanly to the caller. > + } > > if (unlikely(!folio_test_swapcache(folio))) > - return -ENOMEM; > + return -EAGAIN; > > return 0; > } > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 299b5d9e8836..63e8578454ea 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -1257,6 +1257,8 @@ static unsigned int shrink_folio_list(struct list_head *folio_list, > */ > if (folio_test_anon(folio) && folio_test_swapbacked(folio) && > !folio_test_swapcache(folio)) { > + int ret; > + > if (!(sc->gfp_mask & __GFP_IO)) > goto keep_locked; > if (folio_maybe_dma_pinned(folio)) > @@ -1275,10 +1277,10 @@ static unsigned int shrink_folio_list(struct list_head *folio_list, > split_folio_to_list(folio, folio_list)) > goto activate_locked; > } > - if (folio_alloc_swap(folio)) { > + if ((ret = folio_alloc_swap(folio))) { I prefer doing the assignment outside the conditional. > int __maybe_unused order = folio_order(folio); > > - if (!folio_test_large(folio)) > + if (!folio_test_large(folio) || ret != -EAGAIN) > goto activate_locked_split; > /* Fallback to swap normal pages */ > if (split_folio_to_list(folio, folio_list)) > > What’s your view on this, David? I guess returning from folio_alloc_swap() whether a split could allow for swapout (e.g., -E2BIG) would be reasonable. To catch all the cases where it makes a difference: * No free swap space (split won't work) * Some free swap space (split would work) * Sufficient free swap space, but fragmented (split would work) * No memcg space (split won't work) * Some memcg space (split would work) -- Cheers, David