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    SubjectRe: [PATCH 3/14] tmpfs: take control of its truncate_range
    Thanks a lot for looking at these.

    On Tue, 31 May 2011, Christoph Hellwig wrote:
    > > Note that drivers/gpu/drm/i915/i915_gem.c i915_gem_object_truncate()
    > > calls the tmpfs ->truncate_range directly: update that in a separate
    > > patch later, for now just let it duplicate the truncate_inode_pages().
    > > Because i915 handles unmap_mapping_range() itself at a different stage,
    > > we have chosen not to bundle that into ->truncate_range.
    > In your next series that makes it call the readpae replacement directly
    > it might be nice to also call directly into shmem for hole punching.

    (i915 isn't really doing hole-punching there, I think it just found it
    a useful interface to remove the page-and-swapcache without touching
    i_size. Parentheses because it makes no difference to your point.)

    Okay, I'd better do a v2 (probably not before the weekend), and change
    that around to go explicitly to shmem there as well: I'd rather settle
    the interfaces to other subsystems in this series, than mix it with the
    implementation in the next series.

    When I say "shmem", I am including the !SHMEM-was-TINY_SHMEM case too,
    which goes to ramfs. Currently i915 has been configured to disable that
    possibility, though we insisted on it originally: there may or may not be
    good reason for disabling it - may just be a side-effect of the rather
    twisted unintuitive SHMEM/TMPFS dependencies.

    > > I notice that ext4 is now joining ocfs2 and xfs in supporting fallocate
    > > FALLOC_FL_PUNCH_HOLE: perhaps they should support truncate_range, and
    > > tmpfs should support fallocate? But worry about that another time...
    > No, truncate_range and the madvice interface are pretty sad hacks that
    > should never have been added in the first place. Adding
    > FALLOC_FL_PUNCH_HOLE support for shmem on the other hand might make
    > some sense.

    Fine, I'll add tmpfs PUNCH_HOLE later on. And wire up madvise MADV_REMOVE
    to fallocate PUNCH_HOLE, yes?

    Would you like me to remove the ->truncate_range method from
    inode_operations completely? I can do that now, hack directly to tmpfs
    in the interim, in the same way as for i915.


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