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

Ingo Molnar
2020-05-25T07:24:13Z

* Sebastian Andrzej Siewior <bigeasy@linutronix.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