Re: [PATCH v2 6/7] zram: Allocate struct zcomp_strm as per-CPU memory

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2020-05-25 09:24:07 [+0200], Ingo Molnar wrote:
> Various typo/spelling fixes:
> 
> > zcomp::stream is a per-CPU pointer, pointing to struct zcomp_strm 
> > which contains two pointers. Having struct zcomp_strm allocated 
> > directly as per-CPU memory would avoid one additional memory 
> > allocation and a pointer dereference. This also simplifies the 
> > addition of a local_lock to struct zcomp_strm.

thx, updated.

> > diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c
> > index 1a8564a79d8dc..ae6dc137a1ed8 100644
> > --- a/drivers/block/zram/zcomp.c
> > +++ b/drivers/block/zram/zcomp.c
> > @@ -37,19 +37,17 @@ static void zcomp_strm_free(struct zcomp_strm *zstrm)
> >  	if (!IS_ERR_OR_NULL(zstrm->tfm))
> >  		crypto_free_comp(zstrm->tfm);
> >  	free_pages((unsigned long)zstrm->buffer, 1);
> > -	kfree(zstrm);
> > +	zstrm->tfm = NULL;
> > +	zstrm->buffer = NULL;
> >  }
> >  
> >  /*
> >   * allocate new zcomp_strm structure with ->tfm initialized by
> >   * backend, return NULL on error
> >   */
> > -static struct zcomp_strm *zcomp_strm_alloc(struct zcomp *comp)
> > +static int zcomp_strm_alloc(struct zcomp_strm *zstrm,
> > +			    struct zcomp *comp)
> 
> There's no need to put these into two lines, in a single line it's 
> only 73 columns long. Leftover from some earlier bloat?

yup, updated.

> >  void zcomp_stream_put(struct zcomp *comp)
> > @@ -159,16 +157,14 @@ int zcomp_cpu_up_prepare(unsigned int cpu, struct hlist_node *node)
> >  {
> >  	struct zcomp *comp = hlist_entry(node, struct zcomp, node);
> >  	struct zcomp_strm *zstrm;
> > +	int ret;
> >  
> > -	if (WARN_ON(*per_cpu_ptr(comp->stream, cpu)))
> > -		return 0;
> > -
> > -	zstrm = zcomp_strm_alloc(comp);
> > -	if (IS_ERR_OR_NULL(zstrm)) {
> > +	zstrm = per_cpu_ptr(comp->stream, cpu);
> > +	ret = zcomp_strm_alloc(zstrm, comp);
> > +	if (ret) {
> >  		pr_err("Can't allocate a compression stream\n");
> >  		return -ENOMEM;
> 
> BTW., with the allocation being in a single place and us having a 
> proper 'ret', the return -ENOMEM could turn into 'return ret'?

yes.

> Thanks,
> 
> 	Ingo

Sebastian