From: David Rientjes <rientjes@google.com>
To: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Christoph Lameter <cl@linux.com>,
Pekka Enberg <penberg@kernel.org>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Andrew Morton <akpm@linux-foundation.org>,
Vlastimil Babka <vbabka@suse.cz>
Subject: Re: [PATCH] mm, slub: Use prefetchw instead of prefetch
Date: Sun, 10 Oct 2021 15:49:07 -0700 (PDT) [thread overview]
Message-ID: <30a76d87-e0af-3eec-d095-d87e898b31cf@google.com> (raw)
In-Reply-To: <20211008133602.4963-1-42.hyeyoo@gmail.com>
On Fri, 8 Oct 2021, Hyeonggon Yoo wrote:
> It's certain that an object will be not only read, but also
> written after allocation.
>
Why is it certain? I think perhaps what you meant to say is that if we
are doing any prefetching here, then access will benefit from prefetchw
instead of prefetch. But it's not "certain" that allocated memory will be
accessed at all.
> Use prefetchw instead of prefetchw. On supported architecture
If we're using prefetchw instead of prefetchw, I think the diff would be
0 lines changed :)
> like x86, it helps to invalidate cache line when the object exists
> in other processors' cache.
>
> Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
> ---
> mm/slub.c | 7 +++----
> 1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index 3d2025f7163b..2aca7523165e 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -352,9 +352,9 @@ static inline void *get_freepointer(struct kmem_cache *s, void *object)
> return freelist_dereference(s, object + s->offset);
> }
>
> -static void prefetch_freepointer(const struct kmem_cache *s, void *object)
> +static void prefetchw_freepointer(const struct kmem_cache *s, void *object)
> {
> - prefetch(object + s->offset);
> + prefetchw(object + s->offset);
> }
>
> static inline void *get_freepointer_safe(struct kmem_cache *s, void *object)
> @@ -3195,10 +3195,9 @@ static __always_inline void *slab_alloc_node(struct kmem_cache *s,
> note_cmpxchg_failure("slab_alloc", s, tid);
> goto redo;
> }
> - prefetch_freepointer(s, next_object);
> + prefetchw_freepointer(s, next_object);
> stat(s, ALLOC_FASTPATH);
> }
> -
> maybe_wipe_obj_freeptr(s, object);
> init = slab_want_init_on_alloc(gfpflags, s);
>
> --
> 2.27.0
>
>
next prev parent reply other threads:[~2021-10-10 22:49 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-08 13:36 [PATCH] mm, slub: Use prefetchw instead of prefetch Hyeonggon Yoo
2021-10-10 22:49 ` David Rientjes [this message]
2021-10-11 7:21 ` Vlastimil Babka
2021-10-11 10:33 ` Perf and Hackbench results on my machine Hyeonggon Yoo
2021-10-11 13:49 ` Hyeonggon Yoo
2021-10-11 7:23 ` [PATCH] mm, slub: Use prefetchw instead of prefetch Hyeonggon Yoo
2021-10-11 7:20 ` Christoph Lameter
2021-10-11 7:32 ` Hyeonggon Yoo
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