Re: [PATCH] shmem: restore superblock info

[Hugh Dickins <hugh@veritas.com>]

On Mon, 6 Jun 2005, Brent Casavant wrote:
> On Mon, 6 Jun 2005, Hugh Dickins wrote:
> 
> > @@ -1607,15 +1582,17 @@ static int shmem_statfs(struct super_blo
> > -	if (sbinfo) {
> > -		spin_lock(&sbinfo->stat_lock);
> > +	spin_lock(&sbinfo->stat_lock);
...
> 
> This is the only change I'm at all concerned about.

Thanks for noticing, I hadn't really considered that.

> I'm not sure how frequent statfs operations occur in practice (I suspect
> infrequently),

Infrequently, yes.  I think infrequently to the point of never in
the case that concerns you: correct if I'm wrong, someone, but I think
there's actually no handle by which user can statfs shm's internal mount.

> however simply changing the existing code from "if (sbinfo)"
> to "if (sbinfo->max_blocks || sbinfo->max_inodes)" would be an appropriate
> remedy if there is a real problem.

Hadn't thought of that, yes, can do if there's a real problem.

> That said, I'm not all that concerned about it, as my fuzzy memory
> indicates it was the lock/unlock around the statistics updates which
> caused the primary lock contention.

That's right, and certainly this shmem_statfs locking change didn't
show up when you retested for me (thank you!) all those months ago.

Hugh
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