From: Hugh Dickins <hughd@google.com>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: akpm@linux-foundation.org, alex.shi@linux.alibaba.com,
hughd@google.com, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, liwang@redhat.com,
mgorman@techsingularity.net
Subject: Re: [PATCH 2/2] mm, page_alloc: use unlikely() in task_capc()
Date: Tue, 16 Jun 2020 13:29:14 -0700 (PDT) [thread overview]
Message-ID: <alpine.LSU.2.11.2006161319030.1119@eggly.anvils> (raw)
In-Reply-To: <20200616082649.27173-2-vbabka@suse.cz>
On Tue, 16 Jun 2020, Vlastimil Babka wrote:
> Hugh noted that task_capc() could use unlikely(), as most of the time there is
> no capture in progress and we are in page freeing hot path. Indeed adding
> unlikely() redirects produces assembly that better matches the assumption and
> moves all the tests away from the hot path.
>
> I have also noticed that we don't need to test for cc->direct_compaction as the
> only place we set current->task_capture is compact_zone_order() which also
> always sets cc->direct_compaction true.
>
> Suggested-by: Hugh Dickins <hughd@google.com>
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Hugh Dickins <hughd@googlecom>
Thanks for pursuing these, Vlastimil: I'm glad you were able
to remove a test and branch instead of adding one as I had.
One little thing, you've probably gone into this yourself and know
what you've written here is optimal: but I'd rather imagined it with
"unlikely(capc) && ..." instead of "unlikely(capc && ...)" - no need
to respond, please just give it a moment's consideration, Acked anyway.
> ---
> mm/page_alloc.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 48eb0f1410d4..8a4e342d7e8f 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -813,11 +813,10 @@ static inline struct capture_control *task_capc(struct zone *zone)
> {
> struct capture_control *capc = current->capture_control;
>
> - return capc &&
> + return unlikely(capc &&
> !(current->flags & PF_KTHREAD) &&
> !capc->page &&
> - capc->cc->zone == zone &&
> - capc->cc->direct_compaction ? capc : NULL;
> + capc->cc->zone == zone) ? capc : NULL;
> }
>
> static inline bool
> --
> 2.27.0
>
>
next prev parent reply other threads:[~2020-06-16 20:29 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-10 20:48 [PATCH] mm, page_alloc: capture page in task context only Hugh Dickins
2020-06-11 15:43 ` Mel Gorman
2020-06-12 10:30 ` Vlastimil Babka
2020-06-15 21:03 ` Hugh Dickins
2020-06-16 7:45 ` Vlastimil Babka
2020-06-16 8:26 ` [PATCH 1/2] mm, compaction: make capture control handling safe wrt interrupts Vlastimil Babka
2020-06-16 8:26 ` [PATCH 2/2] mm, page_alloc: use unlikely() in task_capc() Vlastimil Babka
2020-06-16 20:29 ` Hugh Dickins [this message]
2020-06-17 9:55 ` Vlastimil Babka
2020-06-22 8:58 ` Mel Gorman
2020-06-16 20:18 ` [PATCH 1/2] mm, compaction: make capture control handling safe wrt interrupts Hugh Dickins
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