linux-kernel - Re: [PATCH v2 6/7] zram: Allocate struct zcomp

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Message-ID: <20200525072407.GE329373@gmail.com>
Date:   Mon, 25 May 2020 09:24:07 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Will Deacon <will@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Minchan Kim <minchan@...nel.org>,
        Nitin Gupta <ngupta@...are.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [PATCH v2 6/7] zram: Allocate struct zcomp_strm as per-CPU memory


* Sebastian Andrzej Siewior <bigeasy@...utronix.de> wrote:

> zcomp::stream is per-CPU pointer, pointing to struct zcomp_strm which
> contains two pointer. Having struct zcomp_strm allocated directly as
> per-CPU memory would avoid one additional memory allocation and a
> pointer dereference.
> This also also simplifies adding a local_lock to struct zcomp_strm.
> 
> Allocate zcomp::stream directly as per-CPU memory.

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.


> 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?

>  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'?

Thanks,

	Ingo