[Bugs] [Bug 1346170] Nested directory creation performance degrade after 100+ iterations 3*3 vol

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1346170

Xavi Hernandez <jahernan at redhat.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|nbalacha at redhat.com         |jahernan at redhat.com
              Flags|                            |needinfo?(jahernan at redhat.c
                   |                            |om)



--- Comment #4 from Xavi Hernandez <jahernan at redhat.com> ---
Based on profile information, the problem seems related to the number of
lookups processed by bricks (they take 99% of the time). Kernel sends a lookup
for each path component before every operation. Given that this tests creates a
nested directory structure, the number of lookups grows linearly as the depth
is greater. The total number of lookups is quadratic on the depth of the
directory.

I see two possible issues here:

1. md-stat should prevent most of the lookup requests to reach the bricks.
2. There are many more lookups than expected (even considering a quadratic
growth).

I'll run a test with latest version and see if any of the previous problems
persist.

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