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Date: Mon, 18 Feb 2013 14:16:24 +0100 From: Martin Steigerwald <Martin@...htvoll.de> To: "Theodore Ts'o" <tytso@....edu> Cc: Subranshu Patel <spatel.ml@...il.com>, linux-ext4@...r.kernel.org Subject: Re: Large buffer cache in EXT4 Am Montag, 18. Februar 2013 schrieb Theodore Ts'o: > On Sun, Feb 17, 2013 at 11:25:39AM +0100, Martin Steigerwald wrote: > > What I never really understand was what is the clear distinction > > between dirty pages and disk block buffers. Why isn´t anything that is > > about to be written to disk in one cache? > > The buffer cache is indexed by physical block number, and each buffer > in the buffer cache is the size of the block size used for I/O to the > device. > > The page cache is indexed by <inode, page frame number>, and each page > is the size of a VM page (i.e.4k for x86 systems, 16k for Power > systems, etc.) > > Certain file systems, including ext3, ext4, and ocfs2, use the jbd or > jbd2 layer to handle their physical block journalling, and this layer > fundamentally uses the buffer cache, since it is concerned with > controlling when specific file system blocks are allowed to ben > written back to the hard drive. Thank you for the explanation, Ted. -- Martin 'Helios' Steigerwald - http://www.Lichtvoll.de GPG: 03B0 0D6C 0040 0710 4AFA B82F 991B EAAC A599 84C7 -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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