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From: Samuel Thibault <samuel.thibault@gnu.org>
Subject: rm -fr slowness

I have always been surprised by the slowness of a mere rm -fr. Looking a
bit inside, I see that diskfs_dirremove_hard() calls diskfs_file_update
(dp, 1) (as does diskfs_truncate, diskfs_direnter_hard, and
diskfs_dirrewrite_hard). diskfs_file_update then calls pager_sync on
the pager, which thus writes back the whole ext2fs pager!

This sounds a bit excessive to me, an unlink could just record it in
memory and actually sync later.  Also, the wait flag is set, so we
really waits for all I/Os, which basically means strictly serializing
file removals: remove one file, wait for the disk to have done it
(~10ms), remove the next one, etc.  I guess this is for safety reasons
against crashes, but isn't the sync option there for such kind of


# IRC, freenode, #hurd, 2011-07-23

    <antrik> youpi: hm... async deletion does have one downside: I just removed
      something to make space, and retried the other command immediately
      afterwards, and it still said "no space left on device"... a few seconds
      later (after the next regular sync I suppose?) it worked
    <youpi> well, that's sorta expected, yes
    <youpi> we get the same on Linux
    <youpi> Mmm, on second thought, I'm not sure how that can happen
    <youpi> the asynchronous thing is for disk writes, not cache writes