* Re: [PATCH 09/18] fs: rework icount to be a locked variable
[not found] ` <1286515292-15882-10-git-send-email-david@fromorbit.com>
@ 2010-10-08 7:27 ` Christoph Hellwig
2010-10-08 7:50 ` Dave Chinner
0 siblings, 1 reply; 4+ messages in thread
From: Christoph Hellwig @ 2010-10-08 7:27 UTC (permalink / raw)
To: Dave Chinner; +Cc: linux-fsdevel, linux-kernel, chris.mason, linux-btrfs
> index 2953e9f..9f04478 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -1964,8 +1964,14 @@ void btrfs_add_delayed_iput(struct inode *inode)
> struct btrfs_fs_info *fs_info = BTRFS_I(inode)->root->fs_info;
> struct delayed_iput *delayed;
>
> - if (atomic_add_unless(&inode->i_count, -1, 1))
> + /* XXX: filesystems should not play refcount games like this */
> + spin_lock(&inode->i_lock);
> + if (inode->i_ref > 1) {
> + inode->i_ref--;
> + spin_unlock(&inode->i_lock);
> return;
> + }
> + spin_unlock(&inode->i_lock);
Yeah, all that i_count/i_ref mess in btrfs needs some serious work.
Chris?
> +
> +/*
> + * inode_lock must be held
> + */
> +void iref_locked(struct inode *inode)
> +{
> + inode->i_ref++;
> +}
> EXPORT_SYMBOL_GPL(iref_locked);
I'm a big fan of _GPL exports, but adding this for a trivial counter
increment seems a bit weird.
> int iref_read(struct inode *inode)
> {
> - return atomic_read(&inode->i_count);
> + int ref;
> +
> + spin_lock(&inode->i_lock);
> + ref = inode->i_ref;
> + spin_unlock(&inode->i_lock);
> + return ref;
> }
There's no need to lock a normal 32-bit variable for readers.
> + inode->i_ref--;
> + if (inode->i_ref == 0) {
if (--inode->i_ref == 0) {
might be a bit more idiomatic.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH 09/18] fs: rework icount to be a locked variable
2010-10-08 7:27 ` [PATCH 09/18] fs: rework icount to be a locked variable Christoph Hellwig
@ 2010-10-08 7:50 ` Dave Chinner
2010-10-08 8:17 ` Christoph Hellwig
0 siblings, 1 reply; 4+ messages in thread
From: Dave Chinner @ 2010-10-08 7:50 UTC (permalink / raw)
To: Christoph Hellwig; +Cc: linux-fsdevel, linux-kernel, chris.mason, linux-btrfs
On Fri, Oct 08, 2010 at 03:27:49AM -0400, Christoph Hellwig wrote:
> > index 2953e9f..9f04478 100644
> > --- a/fs/btrfs/inode.c
> > +++ b/fs/btrfs/inode.c
> > @@ -1964,8 +1964,14 @@ void btrfs_add_delayed_iput(struct inode *inode)
> > struct btrfs_fs_info *fs_info = BTRFS_I(inode)->root->fs_info;
> > struct delayed_iput *delayed;
> >
> > - if (atomic_add_unless(&inode->i_count, -1, 1))
> > + /* XXX: filesystems should not play refcount games like this */
> > + spin_lock(&inode->i_lock);
> > + if (inode->i_ref > 1) {
> > + inode->i_ref--;
> > + spin_unlock(&inode->i_lock);
> > return;
> > + }
> > + spin_unlock(&inode->i_lock);
>
> Yeah, all that i_count/i_ref mess in btrfs needs some serious work.
> Chris?
>
> > +
> > +/*
> > + * inode_lock must be held
> > + */
> > +void iref_locked(struct inode *inode)
> > +{
> > + inode->i_ref++;
> > +}
> > EXPORT_SYMBOL_GPL(iref_locked);
>
> I'm a big fan of _GPL exports, but adding this for a trivial counter
> increment seems a bit weird.
OK, will drop the _GPL.
>
> > int iref_read(struct inode *inode)
> > {
> > - return atomic_read(&inode->i_count);
> > + int ref;
> > +
> > + spin_lock(&inode->i_lock);
> > + ref = inode->i_ref;
> > + spin_unlock(&inode->i_lock);
> > + return ref;
> > }
>
> There's no need to lock a normal 32-bit variable for readers.
Ok, but will need a memory barrier instead?
>
> > + inode->i_ref--;
> > + if (inode->i_ref == 0) {
>
> if (--inode->i_ref == 0) {
>
> might be a bit more idiomatic.
OK.
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH 09/18] fs: rework icount to be a locked variable
2010-10-08 7:50 ` Dave Chinner
@ 2010-10-08 8:17 ` Christoph Hellwig
2010-10-08 13:16 ` Chris Mason
0 siblings, 1 reply; 4+ messages in thread
From: Christoph Hellwig @ 2010-10-08 8:17 UTC (permalink / raw)
To: Dave Chinner
Cc: Christoph Hellwig, linux-fsdevel, linux-kernel, chris.mason, linux-btrfs
On Fri, Oct 08, 2010 at 06:50:01PM +1100, Dave Chinner wrote:
> > There's no need to lock a normal 32-bit variable for readers.
>
> Ok, but will need a memory barrier instead?
Isn't spin_unlock supposed to be one? I'll need some of the locking
experts to shime in.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH 09/18] fs: rework icount to be a locked variable
2010-10-08 8:17 ` Christoph Hellwig
@ 2010-10-08 13:16 ` Chris Mason
0 siblings, 0 replies; 4+ messages in thread
From: Chris Mason @ 2010-10-08 13:16 UTC (permalink / raw)
To: Christoph Hellwig; +Cc: Dave Chinner, linux-fsdevel, linux-kernel, linux-btrfs
On Fri, Oct 08, 2010 at 10:17:14AM +0200, Christoph Hellwig wrote:
> On Fri, Oct 08, 2010 at 06:50:01PM +1100, Dave Chinner wrote:
> > > There's no need to lock a normal 32-bit variable for readers.
> >
> > Ok, but will need a memory barrier instead?
>
> Isn't spin_unlock supposed to be one? I'll need some of the locking
> experts to shime in.
Not really a locking expert, but the locking operations are supposed to
have an implicit barrier.
-chris
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2010-10-08 13:16 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
[not found] <1286515292-15882-1-git-send-email-david@fromorbit.com>
[not found] ` <1286515292-15882-10-git-send-email-david@fromorbit.com>
2010-10-08 7:27 ` [PATCH 09/18] fs: rework icount to be a locked variable Christoph Hellwig
2010-10-08 7:50 ` Dave Chinner
2010-10-08 8:17 ` Christoph Hellwig
2010-10-08 13:16 ` Chris Mason
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).