Hi,
On Wed, 9 Feb 2000 14:30:13 -0500 (EST), Alexander Viro
<[EMAIL PROTECTED]> said:
> On Wed, 9 Feb 2000 [EMAIL PROTECTED] wrote:
>> with 2k blocks and 128 byte fragments, we get to really reduce wasted
>> space below any other system i've ever experienced.
> Erm... I'm afraid that you are missing the point. You will get the
> hardware sectors shared between the files. And you can't pass requess
> smaller than that. _And_ you have to lock the bh when you do IO. Now,
> estimate the fun with deadlocks...
That shoudn't matter. In the new VM it would be pretty trivial for the
filesystem to reserve a separate address_space against which to cache
fragment blocks. Populating that address_space when we want to read a
fragment block doesn't have to be any more complex than populating the
page cache already is. IO itself shouldn't be hard.
Yes, this will end up double-caching fragmented files to some extent,
since we'll have to reserve a separate, non-physically-mapped page for
the tail of a fragmented file.
Allocation/deallocation of fragments themselves obviously has to be done
very carefully, but we already have to deal with that sort of race in
the filesystem for normal allocations --- this isn't really any
different in principle.
--Stephen
