linux-kernel - Re: [PATCH next] mm/vmscan: __isolate_lru_page

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Message-ID: <2ba66325-e3c8-d809-a8dd-85af77c3904b@suse.cz>
Date:   Thu, 26 Nov 2020 16:23:42 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Alex Shi <alex.shi@...ux.alibaba.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Hugh Dickins <hughd@...gle.com>, Yu Zhao <yuzhao@...gle.com>,
        Michal Hocko <mhocko@...e.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH next] mm/vmscan: __isolate_lru_page_prepare clean up

On 11/26/20 3:25 AM, Alex Shi wrote:
> 
> 
> 在 2020/11/26 上午7:43, Andrew Morton 写道:
>> On Tue, 24 Nov 2020 12:21:28 +0100 Vlastimil Babka <vbabka@...e.cz> wrote:
>> 
>>> On 11/22/20 3:00 PM, Alex Shi wrote:
>>>> Thanks a lot for all comments, I picked all up and here is the v3:
>>>>
>>>>  From 167131dd106a96fd08af725df850e0da6ec899af Mon Sep 17 00:00:00 2001
>>>> From: Alex Shi <alex.shi@...ux.alibaba.com>
>>>> Date: Fri, 20 Nov 2020 14:49:16 +0800
>>>> Subject: [PATCH v3 next] mm/vmscan: __isolate_lru_page_prepare clean up
>>>>
>>>> The function just return 2 results, so use a 'switch' to deal with its
>>>> result is unnecessary, and simplify it to a bool func as Vlastimil
>>>> suggested.
>>>>
>>>> Also remove 'goto' by reusing list_move(), and take Matthew Wilcox's
>>>> suggestion to update comments in function.
>>>
>>> I wouldn't mind if the goto stayed, but it's not repeating that much 
>>> without it (list_move() + continue, 3 times) so...
>> 
>> I tried that, and .text became significantly larger, for reasons which
>> I didn't investigate ;)

I found out that comparing whole .text doesn't often work as changes might be lost in alignment, or
once in a while cross the alignment boundary and become exagerated. bloat-o-meter works nice though.

> Uh, BTW, with the gcc 8.3.1 and centos 7, goto or continue version has same size
> on my side with or w/o DEBUG_LIST. But actually, this clean up patch could
> add 10 bytes also with or w/o DEDBUG_LIST.
> 
> Maybe related with different compiler?

gcc (SUSE Linux) 10.2.1 20201117 [revision 98ba03ffe0b9f37b4916ce6238fad754e00d720b]

./scripts/bloat-o-meter vmscan.o.before mm/vmscan.o
add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-1 (-1)
Function                                     old     new   delta
isolate_lru_pages                           1125    1124      -1
Total: Before=57283, After=57282, chg -0.00%

Not surprising, as I'd expect the compiler to figure out by itself that list_move + continue
repeats and can be unified.  The reason for goto to stay would be rather readability (subjective).

> Thanks
> Alex
>