linux-kernel - Re: [PATCH -mm -v3] mm, swap: Sort swap entries before free

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Date:   Tue, 2 May 2017 14:02:28 +0900
From:   Minchan Kim <minchan@...nel.org>
To:     "Huang, Ying" <ying.huang@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Hugh Dickins <hughd@...gle.com>,
        Shaohua Li <shli@...nel.org>, Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH -mm -v3] mm, swap: Sort swap entries before free

On Fri, Apr 28, 2017 at 09:35:37PM +0800, Huang, Ying wrote:
> In fact, during the test, I found the overhead of sort() is comparable
> with the performance difference of adding likely()/unlikely() to the
> "if" in the function.

Huang,

This discussion is started from your optimization code:

        if (nr_swapfiles > 1)
                sort();

I don't have such fast machine so cannot test it. However, you added
such optimization code in there so I guess it's *worth* to review so
with spending my time, I pointed out what you are missing and
suggested a idea to find a compromise.

Now you are saying sort is so fast so no worth to add more logics
to avoid the overhead?
Then, please just drop that if condition part and instead, sort
it unconditionally.