Re: Large buffer cache in EXT4

[Martin Steigerwald <Martin@lichtvoll.de>]

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
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