linux-kernel - Re: [PATCH 02/10] migrate: make core migration code aware of hugepage

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Date:	Tue, 26 Mar 2013 09:49:52 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc:	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mel@....ul.ie>, Hugh Dickins <hughd@...gle.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andi Kleen <andi@...stfloor.org>,
	Hillf Danton <dhillf@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/10] migrate: make core migration code aware of hugepage

On Tue 26-03-13 00:33:35, Naoya Horiguchi wrote:
> On Mon, Mar 25, 2013 at 11:57:01AM +0100, Michal Hocko wrote:
> > On Fri 22-03-13 16:23:47, Naoya Horiguchi wrote:
[...]
> > > +int migrate_movable_pages(struct list_head *from, new_page_t get_new_page,
> > > +			unsigned long private,
> > > +			enum migrate_mode mode, int reason)
> > > +{
> > > +	int err = 0;
> > > +
> > > +	if (!list_empty(from)) {
> > > +		err = migrate_pages(from, get_new_page, private, mode, reason);
> > > +		if (err)
> > > +			putback_movable_pages(from);
> > > +	}
> > > +	return err;
> > > +}
> > > +
> >
> > There doesn't seem to be any caller for this function. Please move it to
> > the patch which uses it.
> 
> I would do like that if there's only one user of this function, but I thought
> that it's better to separate this part as changes of common code
> because this function is commonly used by multiple users which are added by
> multiple patches later in this series.

Sure there is no hard rule for this. I just find it much easier to
review if there is a caller of introduced functionality. In this
particular case I found out only later that many migrate_pages callers
were changed to use mograte_movable_pages and made the
putback_movable_pages cleanup inconsistent between the two.

It would help to mention what is the planned future usage of the
introduced function if you prefer to introduce it without users.

> I mean doing like
> 
>   Patch 1: core change
>   Patch 2: user A (depend on patch 1)
>   Patch 3: user B (depend on patch 1)
>   Patch 4: user C (depend on patch 1)
> 
> is a bit cleaner and easier in bisecting than doing like
> 
>   Patch 1: core change + user A
>   Patch 2: user B (depend on patch 1)
>   Patch 3: user C (depend on patch 1)
> 
> . I'm not sure which is standard or well-accepted way.

Whatever makes the review easy ;)
-- 
Michal Hocko
SUSE Labs
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