Messages in this thread | | | Date | Wed, 07 Mar 2007 08:16:14 +0100 | From | Eric Dumazet <> | Subject | Re: [patch] epoll use a single inode ... |
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Eric Dumazet a écrit : > > 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 ?
Crazy ideas : (some readers are going to kill me)
1) Use the low order bit of f_path.dentry to say : this pointer is not a pointer to a dentry but the inode pointer (with the low order bit set to 1)
OR
2) file->f_path.dentry set to NULL for this special files (so that we dont need to dput() and cache line ping pong the common dentry each time we __fput() a pipe/socket.
Same trick could be used for file->f_path.mnt, because there is a big SMP cache line ping/pong to maintain a mnt_count on pipe/sockets mountpoint while these file systems cannot be un-mounted)
If dentry is NULL, we get the inode pointer from an overlay of struct file_ra_state f_ra; (because for this special files readahead is unused)
This adds some conditional branches of course, but being able to save ram and better use cpu caches might be worth them.
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