Messages in this thread | | | Date | Sat, 10 Jun 2006 02:27:57 +0100 | From | Al Viro <> | Subject | Re: [RFC] Slimming down struct inode |
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On Fri, Jun 09, 2006 at 07:50:08PM -0400, Theodore Ts'o wrote: > 4) i_state and i_flags are both 4-byte longs, but they only need to be > 2-byte shorts, and could be placed next to each other.
void wake_up_inode(struct inode *inode) { /* * Prevent speculative execution through spin_unlock(&inode_lock); */ smp_mb(); wake_up_bit(&inode->i_state, __I_LOCK); }
> 5) Nuke i_cindex. This is only used by ieee1394's > ieee_file_to_instance. There must be another place where we can > store this --- say, in a ieee1394-specific field in struct file? Or > maybe it can be derived some other way, but to chew up 4 bytes in > i_cindex for all inodes just for ieee1394's benefit seems like the > Wrong Thing(tm).
No, it's actually the right thing for _all_ char devices. And it's used before we get a struct file. If anything, ->i_rdev should go long-term...
> 6) Separate out those elements which are only used if the inode is open > into a separate data structure (call it "struct inode_state" for > the sake of argument): > > i_flock, i_mapping, i_data, i_dnotify_mask, i_dnotify, > inotify_watches, inotify_sem, i_state, dirtied_when, > i_size_seqcount, i_mutex, i_alloc_sem > > This is the motherload. Moving these fields out to a separate > structure which is only allocated for inodes which are open will save > a huge amount of memory. But, of course, sweeping through all of the > code which uses these variables to move them would be a major code > change. (We can do it initially with #define magic, but we will need > to audit the code paths to see if it's always to safe to assume that > inode is open before dereferencing the i_state pointer, or whether we > need to check to see if it is valid first.)
It is not safe e.g. for ->i_mutex, since that puppy is used not only when there's an opened file over this inode (or, in fact, before any method had been called for this inode).
It is _certainly_ not safe for ->i_state (take a look at fs/inode.c).
It is not safe for ->i_data, unless you are willing to dispose of page cache on close (even leaving aside such things as directories).
No comments on idiotify fields - IIRC, they can also be used before any ->open() on the inode in question. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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