Re: [PATCH RESEND] mm/vmscan : use vmcan_swappiness( ) basing on MEMCG config to elimiate unnecessary runtime cost

[Zhan Jianyu <nasa4836@gmail.com>]

On Wed, Sep 4, 2013 at 6:47 AM, Johannes Weiner <hannes@cmpxchg.org> wrote:
> On Mon, Aug 26, 2013 at 09:36:58PM +0800, larmbr wrote:
>> Currently, we get the vm_swappiness via vmscan_swappiness(), which
>> calls global_reclaim() to check if this is a global reclaim.
>>
>> Besides, the current implementation of global_reclaim() always returns
>> true for the !CONFIG_MEGCG case, and judges the other case by checking
>> whether scan_control->target_mem_cgroup is null or not.
>>
>> Thus, we could just use two versions of vmscan_swappiness() based on
>> MEMCG Kconfig , to eliminate the unnecessary run-time cost for
>> the !CONFIG_MEMCG at all, and to squash all memcg-related checking
>> into the CONFIG_MEMCG version.
>
> The compiler can easily detect that global_reclaim() always returns
> true for !CONFIG_MEMCG during compile time and not even generate a
> branch for this.
>

Hi, Johannes Weiner,

Thanks for your comment ;)

Andrew has pointed this out and this patch is abandoned.


--

Regards,
Zhan Jianyu

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