Re: [patch] epoll use a single inode ...

From: Eric Dumazet
Date: Wed Mar 07 2007 - 01:53:01 EST


Linus Torvalds a écrit :

I assume that the *only* reason for having multiple dentries is really just the output in /proc/<pid>/fd/, right? Or is there any other reason to have separate dentries for these pseudo-files?

It's a bit sad to waste that much memory (and time) on something like that. I bet that the dentry setup is a noticeable part of the whole sigfd()/timerfd() setup. It's likely also a big part of any memory footprint if you have lots of them.

So how about just doing:
- do a single dentry
- make a "struct file_operations" member function that prints out the name of the thing in /proc/<pid>/fd/, and which *defaults* to just doing the d_path() on the dentry, but special filesystems like this could do something else (like print out a fake inode number from the "file->f_private_data" information)

There seems to really be no downsides to that approach. No existing filesystem will even notice (they'll all have NULL in the new f_op member), and it would allow pipes etc to be sped up and use less memory.


I would definitly *love* saving dentries for pipes (and sockets too), but how are you going to get the inode ?

pipes()/sockets() can use read()/write()/rw_verify_area() and thus need file->f_path.dentry->d_inode (so each pipe needs a separate dentry)

Are you suggesting adding a new "struct file_operations" member to get the inode ?
Or re-intoducing an inode pointer in struct file ?

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