Re: [PATCH] Optimize relay_alloc_page_array() slightly by usingvzalloc rather than vmalloc and memset

From: Mathieu Desnoyers
Date: Sat Oct 30 2010 - 17:52:16 EST


* Jesper Juhl (jj@xxxxxxxxxxxxx) wrote:
> Hi,
>
> We can optimize kernel/relay.c::relay_alloc_page_array() slightly by using
> vzalloc. The patch makes these changes:
>
> - use vzalloc instead of vmalloc+memset.
> - remove redundant local variable 'array'.
> - declare local 'pa_size' as const.

Hrm ? How does declaring a local variable as const helps the compiler in
any way ?

Moreover, is there anyone still using this code ? LTTng uses the Generic
Ring Buffer library which completely deprecates relay.c. Perf and Ftrace
each have their own ring buffers, without dependency on relay.c.

BLK_DEV_IO_TRACE seems to still select RELAY. Has it completed its
transition to either Ftrace or Perf ? Depending on Jens, moving blktrace
relay dependency to the Generic Ring Buffer Library might be a good
option to consider.

Thanks,

Mathieu

>
> Cuts down nicely on both source and object-code size.
>
>
> Signed-off-by: Jesper Juhl <jj@xxxxxxxxxxxxx>
> ---
> Compile tested only.
>
> relay.c | 15 ++++-----------
> 1 file changed, 4 insertions(+), 11 deletions(-)
>
> diff --git a/kernel/relay.c b/kernel/relay.c
> index c7cf397..859ea5a 100644
> --- a/kernel/relay.c
> +++ b/kernel/relay.c
> @@ -70,17 +70,10 @@ static const struct vm_operations_struct relay_file_mmap_ops = {
> */
> static struct page **relay_alloc_page_array(unsigned int n_pages)
> {
> - struct page **array;
> - size_t pa_size = n_pages * sizeof(struct page *);
> -
> - if (pa_size > PAGE_SIZE) {
> - array = vmalloc(pa_size);
> - if (array)
> - memset(array, 0, pa_size);
> - } else {
> - array = kzalloc(pa_size, GFP_KERNEL);
> - }
> - return array;
> + const size_t pa_size = n_pages * sizeof(struct page *);
> + if (pa_size > PAGE_SIZE)
> + return vzalloc(pa_size);
> + return kzalloc(pa_size, GFP_KERNEL);
> }
>
> /*
>
>
>
> --
> Jesper Juhl <jj@xxxxxxxxxxxxx> http://www.chaosbits.net/
> Plain text mails only, please http://www.expita.com/nomime.html
> Don't top-post http://www.catb.org/~esr/jargon/html/T/top-post.html
>

--
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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