Re: [PATCH v2 2/7] quota: add new global dquot list releasing_dquots

[Baokun Li]

On 2023/6/29 18:29, Jan Kara wrote:
> On Wed 28-06-23 21:21:50, Baokun Li wrote:
> > Add a new global dquot list that obeys the following rules:
> >
> >   1). A dquot is added to this list when its last reference count is about
> >       to be dropped.
> >   2). The reference count of the dquot in the list is greater than or equal
> >       to 1 ( due to possible race with dqget()).
> >   3). When a dquot is removed from this list, a reference count is always
> >       subtracted, and if the reference count is then 0, the dquot is added
> >       to the free_dquots list.
> >
> > This list is used to safely perform the final cleanup before releasing
> > the last reference count, to avoid various contention issues caused by
> > performing cleanup directly in dqput(), and to avoid the performance impact
> > caused by calling synchronize_srcu(&dquot_srcu) directly in dqput(). Here
> > it is just defining the list and implementing the corresponding operation
> > function, which we will use later.
> >
> > Suggested-by: Jan Kara <jack@xxxxxxx>
> > Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
> I think you can merge this patch with patch 5. It is not like separating
> this bit helps in review or anything...
OK, I just don't want to cram a lot of stuff into patch 5, I will merge 
this patch
into patch 5 in the next version.
> > diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
> > index 108ba9f1e420..a8b43b5b5623 100644
> > --- a/fs/quota/dquot.c
> > +++ b/fs/quota/dquot.c
> > @@ -226,12 +226,21 @@ static void put_quota_format(struct quota_format_type *fmt)
> >   /*
> >    * Dquot List Management:
> >    * The quota code uses four lists for dquot management: the inuse_list,
>                            ^^^ five now :)
Yes, indeed, I forgot to correct here.
> > - * free_dquots, dqi_dirty_list, and dquot_hash[] array. A single dquot
> > - * structure may be on some of those lists, depending on its current state.
> > + * releasing_dquots, free_dquots, dqi_dirty_list, and dquot_hash[] array.
> > + * A single dquot structure may be on some of those lists, depending on
> > + * its current state.
> >    *
> >    * All dquots are placed to the end of inuse_list when first created, and this
> >    * list is used for invalidate operation, which must look at every dquot.
> >    *
> > + * When the last reference of a dquot will be dropped, the dquot will be
> > + * added to releasing_dquots. We'd then queue work item which would call
> > + * synchronize_srcu() and after that perform the final cleanup of all the
> > + * dquots on the list. Both releasing_dquots and free_dquots use the
> > + * dq_free list_head in the dquot struct. when a dquot is removed from
> 					     ^^^ Capital W please
Good catch！Very sorry for the oversight here.
> > + * releasing_dquots, a reference count is always subtracted, and if
> > + * dq_count == 0 at that point, the dquot will be added to the free_dquots.
> > + *
> 								Honza
Thank you very much for your careful REVIEW! I will fix those in the 
next version!

--
With Best Regards,
Baokun Li
.