Re: [PATCH v6] procfs: Always expose /proc/<pid>/map_files/ and make it readable

[Andrew Morton]

On Mon, 8 Jun 2015 20:39:33 -0700 Calvin Owens <calvinowens@xxxxxx> wrote:

> Currently, /proc/<pid>/map_files/ is restricted to CAP_SYS_ADMIN, and
> is only exposed if CONFIG_CHECKPOINT_RESTORE is set.
> 
> This interface very useful because it allows userspace to stat()
> deleted files that are still mapped by some process, which enables a
> much quicker and more accurate answer to the question "How much disk
> space is being consumed by files that are deleted but still mapped?"
> than is currently possible.

Why is that information useful?

I could perhaps think of some use for "How much disk space is being
consumed by files that are deleted but still open", but to count the
mmapped-then-unlinked files while excluding the opened-then-unlinked
files seems damned peculiar.

IOW, this changelog failed to explain the value of the patch.  Bad
changelog!  Please sell it to us.  Preferably with real-world use
cases.



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