linux-kernel - Re: [Outreachy kernel] [PATCH 5/5] staging: lustre: osc_page.c: Use list_for_each_entry

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Date:   Sun, 5 Mar 2017 18:20:27 +0100 (CET)
From:   Julia Lawall <julia.lawall@...6.fr>
To:     Julia Lawall <julia.lawall@...6.fr>
cc:     simran singhal <singhalsimran0@...il.com>, oleg.drokin@...el.com,
        andreas.dilger@...el.com, jsimmons@...radead.org,
        gregkh@...uxfoundation.org, lustre-devel@...ts.lustre.org,
        devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
        outreachy-kernel@...glegroups.com
Subject: Re: [Outreachy kernel] [PATCH 5/5] staging: lustre: osc_page.c: Use
 list_for_each_entry_safe



On Sun, 5 Mar 2017, Julia Lawall wrote:

>
>
> On Sun, 5 Mar 2017, simran singhal wrote:
>
> > Doubly linked lists which are  iterated  using list_empty
> > and list_entry macros have been replaced with list_for_each_entry_safe
> > macro.
> > This makes the iteration simpler and more readable.
> >
> > This patch replaces the while loop containing list_empty and list_entry
> > with list_for_each_entry_safe.
>
> list_for_each_entry_safe is only needed when the current element is
> removed from the list within the loop body.  If that is not the case, you
> can just use list_for_each_entry.

Sorry, my comment was likely completely off the mark here.  I was thinking
that the original code was using list_for_each.  With the while
(!list_empty pattern, the safe version is definitely needed.

julia

>
> julia
>
>
> >
> > This was done with Coccinelle.
> >
> > @@
> > expression E1;
> > identifier I1, I2;
> > type T;
> > iterator name list_for_each_entry_safe;
> > @@
> >
> > T *I1;
> > + T *tmp;
> > ...
> > - while (list_empty(&E1) == 0)
> > + list_for_each_entry_safe (I1, tmp, &E1, I2)
> > {
> > ...when != T *I1;
> > - I1 = list_entry(E1.next, T, I2);
> > ...
> > }
> >
> > Signed-off-by: simran singhal <singhalsimran0@...il.com>
> > ---
> >  drivers/staging/lustre/lustre/osc/osc_page.c | 11 ++++-------
> >  1 file changed, 4 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/staging/lustre/lustre/osc/osc_page.c b/drivers/staging/lustre/lustre/osc/osc_page.c
> > index ed8a0dc..e8b974f 100644
> > --- a/drivers/staging/lustre/lustre/osc/osc_page.c
> > +++ b/drivers/staging/lustre/lustre/osc/osc_page.c
> > @@ -542,6 +542,7 @@ long osc_lru_shrink(const struct lu_env *env, struct client_obd *cli,
> >  	struct cl_object *clobj = NULL;
> >  	struct cl_page **pvec;
> >  	struct osc_page *opg;
> > +	struct osc_page *tmp;
> >  	int maxscan = 0;
> >  	long count = 0;
> >  	int index = 0;
> > @@ -572,7 +573,7 @@ long osc_lru_shrink(const struct lu_env *env, struct client_obd *cli,
> >  	if (force)
> >  		cli->cl_lru_reclaim++;
> >  	maxscan = min(target << 1, atomic_long_read(&cli->cl_lru_in_list));
> > -	while (!list_empty(&cli->cl_lru_list)) {
> > +	list_for_each_entry_safe(opg, tmp, &cli->cl_lru_list, ops_lru) {
> >  		struct cl_page *page;
> >  		bool will_free = false;
> >
> > @@ -582,8 +583,6 @@ long osc_lru_shrink(const struct lu_env *env, struct client_obd *cli,
> >  		if (--maxscan < 0)
> >  			break;
> >
> > -		opg = list_entry(cli->cl_lru_list.next, struct osc_page,
> > -				 ops_lru);
> >  		page = opg->ops_cl.cpl_page;
> >  		if (lru_page_busy(cli, page)) {
> >  			list_move_tail(&opg->ops_lru, &cli->cl_lru_list);
> > @@ -1043,6 +1042,7 @@ unsigned long osc_cache_shrink_scan(struct shrinker *sk,
> >  {
> >  	struct client_obd *stop_anchor = NULL;
> >  	struct client_obd *cli;
> > +	struct client_obd *tmp;
> >  	struct lu_env *env;
> >  	long shrank = 0;
> >  	u16 refcheck;
> > @@ -1059,10 +1059,7 @@ unsigned long osc_cache_shrink_scan(struct shrinker *sk,
> >  		return SHRINK_STOP;
> >
> >  	spin_lock(&osc_shrink_lock);
> > -	while (!list_empty(&osc_shrink_list)) {
> > -		cli = list_entry(osc_shrink_list.next, struct client_obd,
> > -				 cl_shrink_list);
> > -
> > +	list_for_each_entry_safe(cli, tmp, &osc_shrink_list, cl_shrink_list) {
> >  		if (!stop_anchor)
> >  			stop_anchor = cli;
> >  		else if (cli == stop_anchor)
> > --
> > 2.7.4
> >
> > --
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>