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authorLinus Torvalds <torvalds@linux-foundation.org>2017-07-05 17:00:56 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2017-07-05 17:00:56 -0700
commite5f76a2e0e84ca2a215ecbf6feae88780d055c56 (patch)
tree50c64139c9bdc9dda7efe58e14ad2a81d13114d0 /arch/arm64/net/bpf_jit_comp.c
parentMerge tag 'gfs2-4.13.fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/gfs2/linux-gfs2 (diff)
parentmnt: Make propagate_umount less slow for overlapping mount propagation trees (diff)
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Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace
Pull mnt namespace updates from Eric Biederman: "A big break-through came during this development cycle as a way was found to maintain the existing umount -l semantics while allowing for optimizations that improve the performance. That is represented by the first change in this series moving the reparenting of mounts into their own pass. This has allowed addressing the horrific performance of umount -l on a carefully crafted tree of mounts with locks held (0.06s vs 60s in my testing). What allowed this was not changing where umounts propagate to while propgating umounts. The next change fixes the case where the order of the mount whose umount are being progated visits a tree where the mounts are stacked upon each other in another order. This is weird but not hard to implement. The final change takes advantage of the unchanging mount propgation tree to skip parts of the mount propgation tree that have already been visited. Yielding a very nice speed up in the worst case. There remains one outstanding question about the semantics of umount -l that I am still discussiong with Ram Pai. In practice that area of the semantics was changed by 1064f874abc0 ("mnt: Tuck mounts under others instead of creating shadow/side mounts.") and no regressions have been reported. Still I intend to finish talking that out with him to ensure there is not something a more intense use of mount propagation in the future will not cause to become significant" * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace: mnt: Make propagate_umount less slow for overlapping mount propagation trees mnt: In propgate_umount handle visiting mounts in any order mnt: In umount propagation reparent in a separate pass
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