From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1DA52606A329 for ; Thu, 29 Oct 2026 15:36:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=lists.infradead.org header.i=@lists.infradead.org header.a=rsa-sha256 header.s=bombadil.20210309 header.b=AImUhc9d; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=SvnxR1RE DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Unsubscribe-Post: List-Owner; bh=0MZ+Cdtu8ZetD6MQAGKoqkVifXgXtqYdnKHo/eTOhbs=; b=AImUhc9dDyL/1u vzFDHD4T+6OQudIB19fTenBWsZF++WRKHvwj7qSMzF/mwUSvKqvC4+OgghIb8xUAjqxPOuuU/G7sb IrsjcT6MQNjTe+w019ZSTYkcb32CleYFEag9dPzHXLkakGqxTNlC1gFTNxhu+1U3aLkoU7BRSm1nz NknLAFVvLnmjs5H25On2KNyHL+mXO6aK7pvN2ijh7mMXzWGt4KYmRLyLlUfNXFeNbILs6e62cSyUM dRWvmJ4Sn3CqD3WNApKfq+lZm+v5Hg1UNIKTwixW3rjLjKrgyvnenmVT752EZfrCu10s43cGS1uDe QM7VH0FpVMbm+ces6Axg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.100.1 #2 (Red Hat Linux)) id 1xMSAg-00000009e3i-1W3G; Thu, 29 Oct 2026 15:36:06 +0000 Received: from tor.source.kernel.org ([172.105.4.254]) by bombadil.infradead.org with esmtps (Exim 4.100.1 #2 (Red Hat Linux)) id 1xMSAf-00000009e3G-0Vlt for kexec@lists.infradead.org; Thu, 29 Oct 2026 15:36:05 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id B64FE60267; Thu, 29 Oct 2026 15:36:03 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id EBEE31F01824; Thu, 29 Oct 2026 15:35:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793288163; bh=0MZ+Cdtu8ZetD6MQAGKoqkVifXgXtqYdnKHo/eTOhbs=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=SvnxR1REqXjogeGPFsmkj46v0mjpHOkSNLkbtpJLKJnBH2R57tcgmfFBLxg3pg+tc hyT1sCGbf5V9UaG9pEvhmd/4dZjpLb7ssvKXSN0V7KILMB8LcOXEFLy+Is3AkWvyyS uSMXMe7F5Ryv+os8+r6jBBYCoI2bgM3QV6MI/39SdvciA0pOCwQNuaL5x92OOIZgkI jYsv8a3nz9ca+51kEv6QxK7fMZmRnlAZUIelKhdKNS2pI48R9iE46PIH/2UXUpYFFp b7sZoOi9kvVNaM/xMhYaE69JMYiB1hlPi/NKqIFfmvSD0Fzq0an+EX7an9WJEKizxt w7qkPA0NsvJBg== Message-ID: <957fc9ce-1789-41d7-a4cb-66acdf7fcecb@kernel.org> Date: Thu, 29 Oct 2026 16:21:54 +0100 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 05/46] mm/truncate: look again if a folio left the mapping To: Kiryl Shutsemau Cc: Andrew Morton , Johannes Weiner , Michal Hocko , Qi Zheng , Shakeel Butt , Lorenzo Stoakes , Kairui Song , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , Baolin Wang , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Kees Cook , Peter Zijlstra , Jann Horn , Pedro Falcato , Hugh Dickins , Pasha Tatashin , Pratyush Yadav , "Matthew Wilcox (Oracle)" , Jan Kara , Zi Yan , Lance Yang , Rik van Riel , Harry Yoo , Alistair Popple , Nico Pache , Ryan Roberts , Dev Jain , Usama Arif , Matthew Brost , John Hubbard , Peter Xu , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Oscar Salvador , Minchan Kim , Muchun Song , Xu Xin , Chengming Zhou , Chris Li , Kemeng Shi , Nhat Pham , Youngjun Park , Gregory Price , Joshua Hahn , Rakie Kim , Ying Huang , Jason Gunthorpe , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-cxl@vger.kernel.org, stable@vger.kernel.org, Josef Bacik References: <20261027-fixes_core-v1-0-6f74bec9a5bb@kernel.org> <20261027-fixes_core-v1-5-6f74bec9a5bb@kernel.org> <2f2ef336-2186-4f20-b7f5-565e60471bda@kernel.org> <7fab2115-6c44-43b1-b03b-8ce4a37ffe32@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 X-BeenThere: kexec@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "kexec" X-Spam-Status: No, score=-12.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=4.0.1 X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On 10/29/26 15:38, Kiryl Shutsemau wrote: > On Thu, Oct 29, 2026 at 03:18:23PM +0100, David Hildenbrand (Arm) wrote: >> On 10/29/26 12:37, Kiryl Shutsemau wrote: >>> >>> Yes, I missed that the loop only goes back to start when a lookup >>> comes back empty below end. When the last batch reaches end, it exits >>> without another look. It doesn't need the split either: any punch hole >>> whose last page is in the page cache gets there. >>> >>> That exit looks unintended to me. b9a8a4195c7d ("truncate,shmem: Handle >>> truncates that split large folios") turned the "if (start >= end) goto >>> out" early exit into the loop condition. Before it, the loop went back >>> to start until a lookup from start found nothing; Hugh kept that on >>> purpose for hole punch in 792ceaefe621 ("mm/fs: fix pessimization in >>> hole-punching pagecache"). >>> >>> Restoring it is enough, and makes the "restart to make sure all gone" >>> comment true again: >>> >>> + if (start >= end) >>> + return; >>> + >>> index = start; >>> - while (index < end) { >>> + for (;;) { >>> >>> Then a replaced folio is found on the next round, and truncate needs no >>> special case for it. >>> >> >> But that's then another lookup even if not really required? >> >> Why do you thing that is that better? >> >> I agree that the code is simpler, but at least it's consistent with the other >> handling. > > The extra lookup only happens when the second loop had work to do. > Normally the first pass removes everything, the first lookup from start > comes back empty, and both versions stop there. When the second loop did > run to end, it costs one more lookup over a range that is now empty. > > What I like about it is one way to look again instead of two: the loop > already goes back to start when the last batch ends below end, and the > patch adds a second way for when it ends at end. truncate is not like > shmem here: shmem_undo_range() stops after one sweep on hole punch on > purpose, so it needs the rewind; truncate was meant to sweep until > nothing is left. > > Your version fixes the bug too, so I'll leave the choice to you. > Can we just do: diff --git a/mm/truncate.c b/mm/truncate.c index 733d2713a875..9e9bf029635c 100644 --- a/mm/truncate.c +++ b/mm/truncate.c @@ -475,8 +475,11 @@ void truncate_inode_pages_range(struct address_space *mapping, } } + if (start >= end) + return; + index = start; - while (index < end) { + while (true) { cond_resched(); if (!find_get_entries(mapping, &index, end - 1, &fbatch, indices)) { @@ -499,6 +502,7 @@ void truncate_inode_pages_range(struct address_space *mapping, folio_lock(folio); VM_BUG_ON_FOLIO(!folio_contains(folio, indices[i]), folio); folio_wait_writeback(folio); + /* Do not handle errors, we'll do another lookup */ truncate_inode_folio(mapping, folio); folio_unlock(folio); } @@ -760,7 +764,12 @@ int invalidate_inode_pages2_range(struct address_space *mapping, folio_lock(folio); if (unlikely(folio->mapping != mapping)) { folio_unlock(folio); - continue; + /* + * Folio might have been replaced: look up + * again. + */ + index = indices[i]; + break; } VM_BUG_ON_FOLIO(!folio_contains(folio, indices[i]), folio); folio_wait_writeback(folio); -- 2.43.0 That would be easier for me to digest than the index <= end thing. -- Cheers, David