linux-kernel - Re: [PATCH] mm/vmscan: try to optimize branch procedures.

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Message-ID: <20171128080339.i3ktwm565pz7om4v@dhcp22.suse.cz>
Date:   Tue, 28 Nov 2017 09:03:39 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Jiang Biao <jiang.biao2@....com.cn>
Cc:     akpm@...ux-foundation.org, hannes@...xchg.org,
        hillf.zj@...baba-inc.com, minchan@...nel.org, ying.huang@...el.com,
        mgorman@...hsingularity.net, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, zhong.weidong@....com.cn
Subject: Re: [PATCH] mm/vmscan: try to optimize branch procedures.

On Tue 28-11-17 09:49:45, Jiang Biao wrote:
> 1. Use unlikely to try to improve branch prediction. The
> *total_scan < 0* branch is unlikely to reach, so use unlikely.
> 
> 2. Optimize *next_deferred >= scanned* condition.
> *next_deferred >= scanned* condition could be optimized into
> *next_deferred > scanned*, because when *next_deferred == scanned*,
> next_deferred shoud be 0, which is covered by the else branch.
> 
> 3. Merge two branch blocks into one. The *next_deferred > 0* branch
> could be merged into *next_deferred > scanned* to simplify the code.

How have you measured benefit of this patch?

-- 
Michal Hocko
SUSE Labs