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 A6B913C553A for ; Thu, 2 Jul 2026 08:14:15 +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=1782980056; cv=none; b=Eh86DJaHCDXW3zh69RlW18B0OmWr9pshnAxulyjNEUqxiq7ID6h//W3EfzPAoJAa/Q5PFa7kCw1YXT8qggeHhJ6f7uPtm5nRXNvEXHneHIxU8Y5SFR0lIfhqYUNxSy+vaSZPF1VNJBZLsiQpFPFmwd3muwI2DEa2sW2R3Y554wo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782980056; c=relaxed/simple; bh=3o+WpxfDVtDIsSbuwy/qU1dE/xYy9zwBscQQHp+jIe0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=DY1kQ8CPUFEjb6UlSz3jyPXH6ZDiTQiXBn0P0rztRjMayhQMRzDIweGwN426TcjmpkIOnsEIG5zdmga0vIEpuk/laujXiXJbwlUtcNI2mQW9BCG19CE1e/xbm2Nkm6KZoC9Hc/1exQq/j73CMBR8goJZSDZMkB11Eok2W29diQE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=WcWQ5Tql; 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="WcWQ5Tql" Received: by smtp.kernel.org (Postfix) with ESMTPSA id F330F1F000E9; Thu, 2 Jul 2026 08:14:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782980055; bh=ziK4u5gtjbRoT6EZRzxnYUpobT0bzVvECbdTek69dzY=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=WcWQ5TqlSKMVB1Tp7fGXlKMLSzDSxgw3nuznEa6EqU7T/5Uc5+OE5H9p0YMAFN2+c jtRTTOQKFP1GAZbme+z6T6gmlg+RCOSYprkfxcfxbCJMxdj8EgtZSAVFU+fsxcLL9f wWYCrqR8JQNK+N6NeUtbPMrKawkig8ndkXzAb4FcQjnzqYlmzIA/5xKUM9wsoa3eCe opWWQ2ukY4b4aXvaoHpviYcmRHsrtZ9zxh40aUsnGoyhanGgEEy7S7cFrJXgLA11CZ kWQeco3BEh1kBA2Rv0REnZ1jvYxgb5vJteG4a0SfbQYgJWuoqWLUSv3nWHiinSehB3 G8GUqWf+WNu4g== Message-ID: <3a185a5d-2f2c-4e9d-9cd9-8bdb236dfc5c@kernel.org> Date: Thu, 2 Jul 2026 10:14:08 +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 2/4] mm: drop stale folio_ref_count()==1 check in do_swap_page reuse logic To: "Barry Song (Xiaomi)" , akpm@linux-foundation.org, linux-mm@kvack.org Cc: baoquan.he@linux.dev, chrisl@kernel.org, jp.kobryn@linux.dev, kasong@tencent.com, liam@infradead.org, linux-kernel@vger.kernel.org, ljs@kernel.org, mhocko@suse.com, nphamcs@gmail.com, rppt@kernel.org, shakeel.butt@linux.dev, shikemeng@huaweicloud.com, surenb@google.com, usama.arif@linux.dev, vbabka@kernel.org, youngjun.park@lge.com References: <20260701235955.36126-1-baohua@kernel.org> <20260701235955.36126-3-baohua@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/2/26 01:59, Barry Song (Xiaomi) wrote: > The "we just allocated them without exposing them to the swapcache" > case no longer exists, as Kairui has routed synchronous I/O through > the swapcache as well in his series "unify swapin use swap cache and > cleanup flags"[1]. As a result, folio_ref_count() should never be 1 > in this path, since at least two references are held (base ref plus > swapcache). Remove the folio_ref_count()==1 check and update the > comment accordingly. Sashiko points out two minor things (one flagged as medium, lol, sure sure). Here, you can clarify that folio_ref_count()==1 is true for freshly allocated pages (due to the KSM check) in which case exclusive=true already. > > [1] https://lore.kernel.org/all/20251220-swap-table-p2-v5-0-8862a265a033@tencent.com/ > > Acked-by: Usama Arif > Reviewed-by: Kairui Song > Reviewed-by: Baoquan He > Acked-by: Shakeel Butt > Signed-off-by: Barry Song (Xiaomi) > --- > mm/memory.c | 9 +++------ > 1 file changed, 3 insertions(+), 6 deletions(-) > > diff --git a/mm/memory.c b/mm/memory.c > index 87da78eb1abd..71e9d394816b 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -5046,13 +5046,10 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) > pte = pte_mkuffd_wp(pte); > > /* > - * Same logic as in do_wp_page(); however, optimize for pages that are > - * certainly not shared either because we just allocated them without > - * exposing them to the swapcache or because the swap entry indicates > - * exclusivity. > + * Similar logic as in do_wp_page(); however, optimize for pages that are > + * certainly not because the swap entry indicates exclusivity. s/not/not shared/ but likely you should just simplify to "... pages that are certainly exclusive." > */ > - if (!folio_test_ksm(folio) && > - (exclusive || folio_ref_count(folio) == 1)) { > + if (exclusive) { > if ((vma->vm_flags & VM_WRITE) && !userfaultfd_pte_wp(vma, pte) && > !pte_needs_soft_dirty_wp(vma, pte)) { > pte = pte_mkwrite(pte, vma); -- Cheers, David