linux-kernel - Re: [PATCH v2 2/2] alloc_tag: keep codetag iterator active between read() calls

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Message-ID: <294d0743c0b2e5c409857ef81a6fe8baaf87727f.camel@linux.intel.com>
Date: Fri, 09 May 2025 12:46:06 -0700
From: Tim Chen <tim.c.chen@...ux.intel.com>
To: Suren Baghdasaryan <surenb@...gle.com>
Cc: David Wang <00107082@....com>, kent.overstreet@...ux.dev, 
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v2 2/2] alloc_tag: keep codetag iterator active between
 read() calls

On Fri, 2025-05-09 at 12:36 -0700, Suren Baghdasaryan wrote:
> On Fri, May 9, 2025 at 11:33 AM Tim Chen <tim.c.chen@...ux.intel.com> wrote:
> > 
> > On Sat, 2025-05-10 at 01:39 +0800, David Wang wrote:
> > > 
> > > 
> > > Signed-off-by: David Wang <00107082@....com>
> 
> Acked-by: Suren Baghdasaryan <surenb@...gle.com>
> 
> > > ---
> > >  lib/alloc_tag.c | 29 ++++++++++-------------------
> > >  1 file changed, 10 insertions(+), 19 deletions(-)
> > > 
> > > diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c
> > > index 25ecc1334b67..fdd5887769a6 100644
> > > --- a/lib/alloc_tag.c
> > > +++ b/lib/alloc_tag.c
> > > @@ -45,21 +45,16 @@ struct allocinfo_private {
> > >  static void *allocinfo_start(struct seq_file *m, loff_t *pos)
> > >  {
> > >       struct allocinfo_private *priv;
> > > -     struct codetag *ct;
> > >       loff_t node = *pos;
> > > 
> > > -     priv = kzalloc(sizeof(*priv), GFP_KERNEL);
> > > -     m->private = priv;
> > > -     if (!priv)
> > > -             return NULL;
> > > -
> > > -     priv->print_header = (node == 0);
> > > +     priv = (struct allocinfo_private *)m->private;
> > >       codetag_lock_module_list(alloc_tag_cttype, true);
> > > -     priv->iter = codetag_get_ct_iter(alloc_tag_cttype);
> > > -     while ((ct = codetag_next_ct(&priv->iter)) != NULL && node)
> > > -             node--;
> > > -
> > > -     return ct ? priv : NULL;
> > > +     if (node == 0) {
> > > +             priv->print_header = true;
> > > +             priv->iter = codetag_get_ct_iter(alloc_tag_cttype);
> > > +             codetag_next_ct(&priv->iter);
> > > +     }
> > 
> > Do you need to skip print header when *pos != 0? i.e add
> 
> Technically not needed since proc_create_seq_private() allocates
> seq->private using kzalloc(), so the initial value of
> priv->print_header is always false.

But we'll start with first call to allocinfo_start() with *pos == 0, 
then print_header will be initialized to true.
Will there be subsequent calls of allocinfo_start() with *pos !=0,
but priv->print_header stays at 0? 

Tim
> 
> > 
> >         } else {
> >                 priv->print_header = false;
> >         }
> > 
> > Tim
> > 
> > > +     return priv->iter.ct ? priv : NULL;
> > >  }
> > > 
> >