On Thu, Jun 11, 2015 at 9:49 PM, Andrew Morton <a...@linux-foundation.org> wrote: > On Thu, 11 Jun 2015 14:10:45 +0300 Alexey Dobriyan <adobri...@gmail.com> > wrote: > >> On Wed, Jun 10, 2015 at 11:58 PM, Andrew Morton >> <a...@linux-foundation.org> wrote: >> > On Tue, 9 Jun 2015 18:39:02 -0700 Calvin Owens <calvinow...@fb.com> wrote: >> > >> >> On Tuesday 06/09 at 14:13 -0700, Andrew Morton wrote: >> >> > On Mon, 8 Jun 2015 20:39:33 -0700 Calvin Owens <calvinow...@fb.com> >> >> > 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. >> >> >> >> Let's phrase the question a bit more generically: >> >> >> >> "How much disk space is being consumed by files that have been >> >> unlinked, but are still referenced by some process?" >> >> >> >> There are two pieces to this problem: >> >> 1) Unlinked files that are still open (whether mapped or not) >> >> 2) Unlinked files that are not open, but are still mapped >> >> >> >> You can track down everything in (1) using /proc/<pid>/fd/*, and you >> >> can use stat() to figure out how much space they're using. >> > >> > This doesn't work if the mapped file has been unlinked? What does the >> > /proc/pid/map_files listing look like for these? >> >> It says "(deleted)" like /proc/*/exe or any other symlink. > > Actually the symlink directs at "/home/akpm/foo (deleted)".
I meant exactly that: full path + (deleted). > And lo, if you do `stat -L' on the symlink, you get the info for the > unlinked-but-still-mmapped inode. I never knew that. And I wouldn't > have learned it from the documentation, which is careful to keep all > this a secret. Yes, map_files symlinks allow to reach descriptors in the very same way /proc/*/fd symlinks allow to reach descriptors. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
