linux-kernel - Re: [PATCH] mm: thp: remove use_zero

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Message-Id: <20180720123243.6dfc95ba061cd06e05c0262e@linux-foundation.org>
Date:   Fri, 20 Jul 2018 12:32:43 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Yang Shi <yang.shi@...ux.alibaba.com>
Cc:     kirill@...temov.name, hughd@...gle.com, rientjes@...gle.com,
        aaron.lu@...el.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: thp: remove use_zero_page sysfs knob

On Sat, 21 Jul 2018 02:13:50 +0800 Yang Shi <yang.shi@...ux.alibaba.com> wrote:

> By digging into the original review, it looks use_zero_page sysfs knob
> was added to help ease-of-testing and give user a way to mitigate
> refcounting overhead.
> 
> It has been a few years since the knob was added at the first place, I
> think we are confident that it is stable enough. And, since commit
> 6fcb52a56ff60 ("thp: reduce usage of huge zero page's atomic counter"),
> it looks refcounting overhead has been reduced significantly.
> 
> Other than the above, the value of the knob is always 1 (enabled by
> default), I'm supposed very few people turn it off by default.
> 
> So, it sounds not worth to still keep this knob around.

Probably OK.  Might not be OK, nobody knows.

It's been there for seven years so another six months won't kill us. 
How about as an intermediate step we add a printk("use_zero_page is
scheduled for removal.  Please contact linux-mm@...ck.org if you need
it").