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References: <20230308080327.33906-1-chengen.du@canonical.com> <84E89457-478E-42F8-AC5F-DFFC58FBEFFB@hammerspace.com>
In-Reply-To: <84E89457-478E-42F8-AC5F-DFFC58FBEFFB@hammerspace.com>
From:   Anna Schumaker <anna@kernel.org>
Date:   Tue, 14 Mar 2023 15:47:14 -0400
Message-ID: <CAFX2JfkR3exLZUYS6mydhS-putG+6WoHjP790NJbXOQCw3McJQ@mail.gmail.com>
Subject: Re: [PATCH] NFS: Correct timing for assigning access cache timestamp
To:     Trond Myklebust <trondmy@hammerspace.com>
Cc:     Chengen Du <chengen.du@canonical.com>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Tue, Mar 14, 2023 at 2:51=E2=80=AFPM Trond Myklebust <trondmy@hammerspac=
e.com> wrote:
>
>
>
> > On Mar 8, 2023, at 03:03, Chengen Du <chengen.du@canonical.com> wrote:
> >
> > When the user's login time is newer than the cache's timestamp,
> > the original entry in the RB-tree will be replaced by a new entry.
> > Currently, the timestamp is only set if the entry is not found in
> > the RB-tree, which can cause the timestamp to be undefined when
> > the entry exists. This may result in a significant increase in
> > ACCESS operations if the timestamp is set to zero.
> >
> > Signed-off-by: Chengen Du <chengen.du@canonical.com>
> > ---
> > fs/nfs/dir.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
> > index a41c3ee4549c..6fbcbb8d6587 100644
> > --- a/fs/nfs/dir.c
> > +++ b/fs/nfs/dir.c
> > @@ -3089,7 +3089,6 @@ static void nfs_access_add_rbtree(struct inode *i=
node,
> > else
> > goto found;
> > }
> > - set->timestamp =3D ktime_get_ns();
> > rb_link_node(&set->rb_node, parent, p);
> > rb_insert_color(&set->rb_node, root_node);
> > list_add_tail(&set->lru, &nfsi->access_cache_entry_lru);
> > @@ -3114,6 +3113,7 @@ void nfs_access_add_cache(struct inode *inode, st=
ruct nfs_access_entry *set,
> > cache->fsgid =3D cred->fsgid;
> > cache->group_info =3D get_group_info(cred->group_info);
> > cache->mask =3D set->mask;
> > + cache->timestamp =3D ktime_get_ns();
> >
> > /* The above field assignments must be visible
> > * before this item appears on the lru.  We cannot easily
> > --
> > 2.37.2
> >
>
> Doh! Nice catch=E2=80=A6
>
> Anna, please pick this up for 6.2-rcX and add an appropriate
>
> Fixes: 0eb43812c027 ("NFS: Clear the file access cache upon login=E2=80=
=9D)

Will do!

Anna
>
> Thanks!
>   Trond
>
> _________________________________
> Trond Myklebust
> Linux NFS client maintainer, Hammerspace
> trond.myklebust@hammerspace.com
>