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 4C5A449A3D0 for ; Fri, 18 Sep 2026 13:52:05 +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=1789739527; cv=none; b=GbPnC+/7sMULOkVUijc2ZZfYjB6Xhuyw1KHjSf67RBptAPjr8vwfNrv0DjdFC+tTqtdgdlumQ+/Z0t32luw9bDTnlIS2tzoeMeO/rvwXUvHrhZzYr9pplwWrs0HEDkHHcn0GoRhaqUEEYDaQXhr+XZhCkR7VgllT3IOulbvt+4g= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789739527; c=relaxed/simple; bh=KsQ6JItTfJ2vyWtOR6lCqcdQtSLKslfjN3Eosk25OKY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=CoCIjdHW/JG6RUob7gb4D4NGm6BzTRrWFwVUJcLFRya3xYOByE0KDrN1vB2kZB+8FI8rwd2+IytT6zZ8grQTNW8Dtn8qogPIKUkfyJl89Osa7gb3JmhycJ/QEG29ZoqXpx8x4Fqk3EbildQ7Pt6rNxHdbgfVgsHXaOVT3gf/TS4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=X2YePAF5; 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="X2YePAF5" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2088D1F000FF; Fri, 18 Sep 2026 13:52:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789739525; bh=pigOYWPBo4f31CFMisvTOnx1I+B1RAOmv4zggET0Nwc=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=X2YePAF53WPKG42GvCaXfl9rzwpcUTq3WUhHUkxjkRWik1oB3RWNeqcywlR8F3GO8 28asPiOH+88PPpnpNJ3Olc1MDvf6jfgRE74fmS4KRQzpWFM7clBzjxF+6OHt5Vor1R NxO5794YuK5jzFBOU4oZtZk8IsymnHrkrAosqsLdWEb1l0QpEokKrq3xkDwHJG2bxP IW6XP9lOS9LVq2YmYC7umJJDblB+IT4e/Jh/B6CnWE3Xp9YSimYyHEAedbKCDigi4s ODYaMYjACQSI1vdSCP9SDeSZ53xBGvv4UPw22jbQQfQjmGN4QITuiSiCftcV2eWV+1 ZVqE4BHWCLHOw== Message-ID: <0e0a0908-8e5d-4cee-9fbb-ce730bb662e1@kernel.org> Date: Fri, 18 Sep 2026 15:51:59 +0200 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v9 14/15] filemap: Add support for authoritative mappings To: "Matthew Wilcox (Oracle)" , Andrew Morton , Jane Chu , linux-mm@kvack.org Cc: Muchun Song , Oscar Salvador , Miaohe Lin , Naoya Horiguchi , Jan Kara , linux-fsdevel@vger.kernel.org, Christian Brauner , Jiaqi Yan References: <20260805210557.1118966-1-willy@infradead.org> <20260805210557.1118966-15-willy@infradead.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 8/5/26 23:05, Matthew Wilcox (Oracle) wrote: > An authoritative mapping knows about all the folios in the mapping. > If read() finds a missing folio, there's no reason to allocate one and > try to read it because we know it's a zero region of the file. We can > just call iov_iter_zero() instead. > > Signed-off-by: Matthew Wilcox (Oracle) > Reviewed-by: Jane Chu > --- > include/linux/pagemap.h | 11 +++++++++++ > mm/filemap.c | 18 ++++++++++++++++++ > 2 files changed, 29 insertions(+) > > diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h > index 968b791cfd14..22d48935ffda 100644 > --- a/include/linux/pagemap.h > +++ b/include/linux/pagemap.h > @@ -210,6 +210,7 @@ enum mapping_flags { > AS_WRITEBACK_MAY_DEADLOCK_ON_RECLAIM = 9, > AS_KERNEL_FILE = 10, /* mapping for a fake kernel file that shouldn't > account usage to user cgroups */ > + AS_AUTHORITATIVE = 11, /* If we miss in the page cache, it's a hole */ Just curious if "in-memory file system" would be a different way of looking at it. There, a hole in the page cache always expresses a hole in the file. AS_IN_MEMORY_FILE Just an idea, because that's why I always had in mind regarding that (all state in memory). -- Cheers, David