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