linux-kernel - Re: [PATCH v2 0/3] trim the uses of compound

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Date:   Fri, 26 Feb 2021 12:04:07 -0700
From:   Yu Zhao <yuzhao@...gle.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     akpm@...ux-foundation.org, alex.shi@...ux.alibaba.com,
        willy@...radead.org, guro@...com, hannes@...xchg.org,
        hughd@...gle.com, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        mhocko@...nel.org, vdavydov.dev@...il.com,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH v2 0/3] trim the uses of compound_head()

On Fri, Feb 26, 2021 at 11:52:03AM +0100, Vlastimil Babka wrote:
> On 2/26/21 10:17 AM, Yu Zhao wrote:
> > Patch series "mm: lru related cleanups" starting at commit 42895ea73bcd
> > ("mm/vmscan.c: use add_page_to_lru_list()") bloated vmlinux by 1777
> > bytes, according to:
> >   https://lore.kernel.org/linux-mm/85b3e8f2-5982-3329-c20d-cf062b8da71e@suse.cz/
> 
> Huh, I thought Andrew didn't want to send it for 5.12:
> https://lore.kernel.org/linux-mm/20210223145011.0181eed96ab0091a493b51f6@linux-foundation.org/
> 
> > It turned out many places inline Page{Active,Unevictable} which in
> > turn include compound_head().
> > 
> > From the v1:
> >   Removing compound_head() entirely from Page{Active,Unevictable} may
> >   not be the best option (for the moment) because there may be other
> >   cases that need compound_head().
> > 
> > In addition to picking a couple pieces of low-hanging fruit, this v2
> > removes compound_head() completely from Page{Active,Unevictable}.
> > 
> > bloat-o-meter result before and after the series:
> >   add/remove: 0/0 grow/shrink: 6/92 up/down: 697/-7656 (-6959)
> 
> Good that you found a way to more than undo the bloat then. But we need to be
> careful so bugs are not introduced due to pressure to not have bloated 5.12.

I was very conservative and only picked a few pieces of low-hanging
fruit. The pressure is good -- if you hadn't noticed it and Andrew
hadn't been emphatic about it, it'd have been left for another time
and to another person, and so on.