Derek Atkins wrote:
> Harald Barth <[EMAIL PROTECTED]> writes:
>
> > > Unfortunately, the AFS cache does not meet those conditions. The cache is
> > > a single directory that may have tens of thousands of files in it.
> >
> > This is a design miss of the AFS cache which will give problems for
> > almost all flavours of *i*x file systems. It can only win by a change.
> > A change can go in two directions: Order the files in some directory
> > tree with some smart structure or give up the files approach and use
> > one big file. When using -memcache, the whole cache is one big chunk
> > of data, too. Another pain is this bad habit of creating all the
> > inodes at boot. If I start with a really small cache and later
> > increase the cache size on the fly, inodes are created without
> > blocking cache operations for minutes. So why the wait at boot? This
> > feature seems to be wanted by more than a few.
>
> I'm not convinced this is a design miss.. The cache manager needs to
> walk the cache to see what's in it, and then it can random-access into
> the cache at a later time. This implies that it has to walk the
> directory at the beginning, so it doesn't matter how long it takes to
> walk it. Subsequenty, it caches the inode number so it doesn't need
> to go through the directory for future accesses. So, indeed, I think
> the current design is actually very clever. The problem is that
> reiserfs doesn't use the inode (by itself) to key into the filesystem
> like pretty much every other FS in existence.
>
> > Harald.
>
> -derek
I do not agree. AFAIK a filesystem is allowed to move its files around. So just
imagine that real locations of files data and metadata are moving all the time. (A
filesystem must be allowed to repack its data, for resizing or defragmentation for
example.) The way to catch a filename|directory entry (which has its file
associated) is to use that filename. The way to catch just the file is to use a
fd. If you want to catch the file for a long time independent of its name and you
think that fds are too expensive, you better create a (hard) link. Anything else
is using filesystem internals. (A file is defined to be reachable within a
filesystem if and only if the sum of its link count and its open count is greater
than 0. The link count is the number of directory entries a file is referenced by,
the open count is the number of times a file is opened.)
What you could do, if your original filename does not change, is to ask the
filesystem for a hint to be passed later back to the filesystem to find the file
more quickly than by name. But as usual with hints, the hint may fail, so you
cannot ommit the filename of the file you mentioned.
Xu�n.
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