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Interface proposal for dentry grouping

From:  Glauber Costa <>
Subject:  [RFC 0/5] Interface proposal for dentry grouping
Date:  Mon, 25 Jul 2011 19:16:39 +0400
Message-ID:  <>
Cc:  Pavel Emelyanov <>, Al Viro <>, Hugh Dickins <>, Nick Piggin <>, Andrea Arcangeli <>, Rik van Riel <>, Dave Hansen <>, David Chinner <>, Glauber Costa <>
Archive-link:  Article

Hello folks,

If you would remember, Pavel recently posted a series proposing a way 
of grouping entries in the dcache, in order to in the future limit the
per-container dcache size growth

At the time, a proper interface for proper operation of those entities was
missing. This patchset contains my proposal on how to do so. Note that I am not
reposting Pavel original series (+ changes) this time. This is on purpose, since
I want to focus on the interface here.

So here's briefly what I am proposing:

* dentry groups are created per-mntpoint. Combined with our ability to bind mount,
  this means that we can specify a dentry group root to be at any arbitrary point
  of the filesystem.
* Also, per-mntpoint also ties the dentry groups to a fs-independent entity, 
  instead of a super-block, which is tied to a filesystem / real mount.
* Any mount helper is able to pass arbitrary strings to mount(). I build on it by
  allowing the generic vfs code to parse these options. A reference to a super
  block is hard to obtain at this point, which is one more reason (given of course
  this interface will be liked) to tie this to a mntpoint, not sb.
* Although options to the vfs are a new thing introduced here, mount() is a natural way
  to specify attributes of a filesystem hierarchy, I believe.

Glauber Costa (5):
  Accept per-mntpoint named options
  introduce dentry_is_mob_root
  parse options at mount operation
  destroy 0-sized mobs
  save mnt info in do_loopback.

 fs/dcache.c            |   11 ++++++
 fs/namespace.c         |   84 ++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/dcache.h |    1 +
 include/linux/mount.h  |    2 +
 4 files changed, 98 insertions(+), 0 deletions(-)


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