Linux-kernel mailing list archive 1999-22,: Re: XFS and journalling filesystems

# Re: XFS and journalling filesystems

Stephen C. Tweedie (sct@redhat.com)
Wed, 2 Jun 1999 00:18:38 +0100 (BST)

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Hi,

On Tue, 01 Jun 1999 02:06:09 -0700, Dan Koren
<dkoren@cthulhu.engr.sgi.com> said:

> This is not a problem in page cache systems like Irix, Solaris or
> SVR4 (UnixWare).

and in Linux. The fact that there is a buffer cache used for some parts
of the write path doesn't stop us keeping the page cache consistent at
all times. In 2.3, the two paths will use the same memory anyway.

> File data is kept in the page cache, not in the buffer cache, and the
> same page(s) are mapped or accessed by all the processes that access a
> file. If a process writes to a file the new data becomes visible to
> all readers of the file as soon as the write system call has
> completed.

Agreed, that's what is required by Unix file semantics. The
cache-to-disk synchronisation semantics are much more relaxed. Lazy
batching of the metadata transactions on disk is perfectly legal on
Unix.

--Stephen

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