[Gluster-devel] triggers for sending inode forgets

[Anand Avati]

On Fri, Jul 4, 2014 at 7:03 PM, Pranith Kumar Karampuri <pkarampu at redhat.com
> wrote:

> hi,
>     I work on glusterfs and was debugging a memory leak. Need your help in
> figuring out if something is done properly or not.
> When a file is looked up for the first time in gluster through fuse,
> gluster remembers the parent-inode, basename for that inode. Whenever an
> unlink/rmdir/(lookup gives ENOENT) happens then corresponding forgetting of
> parent-inode, basename happens.


This is because of the path resolver explicitly calls d_invalidate() on a
dentry when d_revalidate() fails on it.

In all other cases it relies on fuse to send forget of an inode to release
> these associations. I was wondering what are the trigger points for sending
> forgets by fuse.
>
> Lets say M0, M1 are fuse mounts of same volume.
> 1) Mount 'M0' creates a file 'a'
> 2) Mount 'M1' of deletes file 'a'
>
> M0 never touches 'a' anymore. Will a forget be sent on inode of 'a'? If
> yes when?
>

Really depends on when the memory manager decides to start reclaiming
memory from dcache due to memory pressure. If the system is not under
memory pressure, and if the stale dentry is never encountered by the path
resolver, the inode may never receive a forget. To keep a tight utilization
limit on the inode/dcache, you will have to proactively fuse_notify_inval_entry
on old/deleted files.

Thanks
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