On Fri, 2010-05-14 at 13:32 -0400, Chuck Lever wrote:
> On 05/14/10 01:13 PM, Trond Myklebust wrote:
> > On Fri, 2010-05-14 at 12:34 -0400, Chuck Lever wrote:
> >> On 05/13/10 05:08 PM, Trond Myklebust wrote:
> >>> Signed-off-by: Trond Myklebust<Trond.Myklebust@xxxxxxxxxx>
> >>> ---
> >>> net/sunrpc/auth.c | 5 ++---
> >>> 1 files changed, 2 insertions(+), 3 deletions(-)
> >>>
> >>> diff --git a/net/sunrpc/auth.c b/net/sunrpc/auth.c
> >>> index 2213dc5..5fb02ac 100644
> >>> --- a/net/sunrpc/auth.c
> >>> +++ b/net/sunrpc/auth.c
> >>> @@ -236,6 +236,8 @@ rpcauth_prune_expired(struct list_head *free, int nr_to_scan)
> >>>
> >>> list_for_each_entry_safe(cred, next,&cred_unused, cr_lru) {
> >>>
> >>> + if (nr_to_scan-- == 0)
> >>> + break;
> >>> /*
> >>> * Enforce a 60 second garbage collection moratorium
> >>> * Note that the cred_unused list must be time-ordered.
> >>> @@ -255,11 +257,8 @@ rpcauth_prune_expired(struct list_head *free, int nr_to_scan)
> >>> get_rpccred(cred);
> >>> list_add_tail(&cred->cr_lru, free);
> >>> rpcauth_unhash_cred_locked(cred);
> >>> - nr_to_scan--;
> >>> }
> >>> spin_unlock(cache_lock);
> >>> - if (nr_to_scan == 0)
> >>> - break;
> >>> }
> >>> return (number_cred_unused / 100) * sysctl_vfs_cache_pressure;
> >>> }
> >>
> >> It looks to me like the mm calls our cache shrinker with nr_to_scan set
> >> to zero when it just wants this return value, and nothing more. But the
> >> logic here seems to assume that nr_to_scan == 0 means shrink as much as
> >> you can. Am I reading this correctly?
> >
> > Look more carefully: the comparison contains a post-decrement operation,
> > so if the nr_to_scan == 0, then we immediately exit the loop (after
> > decrementing nr_to_scan, but who cares about that)...
>
> When mm calls with nr_to_scan set to zero, it doesn't expect a -1
> return, it just uses the returned value. mm checks for a -1 return only
> when a non-zero scan count argument is passed.
>
> So the check you added here (and in the access cache shrinker) to return
> -1 when the gfp_mask doesn't contain GFP_KERNEL could cause some
> trouble. It would be safer if we return -1 _after_ checking for
> nr_to_scan == 0.
Oh... You're referring to the change that was added in Patch 6/15
SUNRPC: Dont run rpcauth_cache_shrinker() when gfp_mask is GFP_NOFS? I
got confused...
I can perhaps rather add a check for nr_to_scan != 0 in that patch...
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