Re: [PATCH 5/6] Teach "fsck" not to follow subproject links

On Wed, 11 Apr 2007, Linus Torvalds wrote:

On Thu, 12 Apr 2007, Sam Vilain wrote:

The reason a *full* global fsck is so expensive is that it would have an
absolutely humungous working set, and effectively keep everything in
memory through it all. Doing it in stages ("fsck smaller individiual trees
separately") is actually the same amount of absolute work, but the working
set never grows, so it scales much better.

(fsck'ing projects individually also happens to allow you to do the
sub-project fsck's in parallel across multiple CPU's or multiple machines,
so it actually scales much better that way too - but the big problem
tends to be excessive memory use, so the "SMP parallel version" only
makes sense if you have tons of memory and can afford to do these things
at the same time!)

would it make sense to have a --multiple-project option for fsck that would let 
you specify multiple 'projects' that share a object set and have the default 
checking not do the reachability checks that cause problems in this case?

Then people can share the objects if they want to and still do a full check, but 
would get warned that the full check would take a lot of time. which is not a 
big problem for a housekeeping thing that's run infrequently to find unreachable 
objects (which is something that should seldom happen in a well managed project)

David Lang