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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 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 X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: A6E9818000A X-Stat-Signature: 53etct7besa97yhrmm5mifyowfnq6bhr X-Rspam-User: X-HE-Tag: 1789739526-396001 X-HE-Meta: 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 488wIwKU PHsx3ORO9Z0MMqzhxKUYYj4872sTu2hiC9P9BPj49CadAklX/iGGNNRNmv5pdDUrjZwCadAayO3GSKUcRboznVK/aqwxng6H4LRWHZXhVbdB2AKMFW/Ld6Z9yCtSgjcEegPImCiOHGm06vEA+U6VGhfPUaAU4NkVJsORcSQyNfiAM3hG7Dvc4dqNiRGhlgABJ4zpmpOFXbtQPu00RM0QGfJnhcwWk3lL/bglzDll9tJAsqr8lIt6wwhKDsK0cUhYab5RXgLMeyHgr6IZvTKtlNmNpgRd5pNgRYyHDbBTuMn794cVbEWmq7v+tf6+mWLwldEkU+HQf0wsQ6L0CJAcGQKK1u8ky5FnSqGX5vR9cGJstMvRhUE/UsmMINkWfD6Q7SAeffby491UfqTlA9uDRKx5cmxrh8pWCzLHJ Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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