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    SubjectRe: [PATCH][RFC] fast file mapping for loop
    On Thu, Jan 10 2008, Chris Mason wrote:
    > On Thu, 10 Jan 2008 08:54:59 +0000
    > Christoph Hellwig <hch@infradead.org> wrote:
    >
    > > On Thu, Jan 10, 2008 at 09:44:57AM +0100, Jens Axboe wrote:
    > > > > IMHO this shouldn't be done in the loop driver anyway.
    > > > > Filesystems have their own effricient extent lookup trees (well,
    > > > > at least xfs and btrfs do), and we should leverage that instead
    > > > > of reinventing it.
    > > >
    > > > Completely agree, it's just needed right now for this solution
    > > > since all we have is a crappy bmap() interface to get at those
    > > > mappings.
    > >
    > > So let's fix the interface instead of piling crap ontop of it. As I
    > > said I think Peter has something to start with so let's beat on it
    > > until we have something suitable. If we aren't done by end of Feb
    > > I'm happy to host a hackfest to get it sorted around the fs/storage
    > > summit..
    > >
    >
    > Ok, I've been meaning to break my extent_map code up, and this is a
    > very good reason. I'll work up a sample today based on Jens' code.

    Great!

    > The basic goals:
    >
    > * Loop (swap) calls into the FS for each mapping. Any caching happens
    > on the FS side.
    > * The FS returns an extent, filling any holes

    We don't want to fill holes for a read, but I guess that's a given?

    > Swap would need to use an extra call early on for preallocation.
    >
    > Step two is having a call back into the FS allow the FS to delay the
    > bios until commit completion so that COW and delalloc blocks can be
    > fully on disk when the bios are reported as done. Jens, can you add
    > some way to queue the bio completions up?

    Sure, a function to save a completed bio and a function to execute
    completions on those already stored?

    --
    Jens Axboe



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