linux-kernel - Re: [PATCH 02/12] mm: introduce page_check

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Message-Id: <20170124145513.1c0687179eceaac43523da56@linux-foundation.org>
Date:   Tue, 24 Jan 2017 14:55:13 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Hugh Dickins <hughd@...gle.com>,
        Rik van Riel <riel@...hat.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/12] mm: introduce page_check_walk()

On Wed, 25 Jan 2017 01:50:30 +0300 "Kirill A. Shutemov" <kirill@...temov.name> wrote:

> > > + * @pcw->ptl is unlocked and @pcw->pte is unmapped.
> > > + *
> > > + * If you need to stop the walk before page_check_walk() returned false, use
> > > + * page_check_walk_done(). It will do the housekeeping.
> > > + */
> > > +static inline bool page_check_walk(struct page_check_walk *pcw)
> > > +{
> > > +	/* The only possible pmd mapping has been handled on last iteration */
> > > +	if (pcw->pmd && !pcw->pte) {
> > > +		page_check_walk_done(pcw);
> > > +		return false;
> > > +	}
> > > +
> > > +	/* Only for THP, seek to next pte entry makes sense */
> > > +	if (pcw->pte) {
> > > +		if (!PageTransHuge(pcw->page) || PageHuge(pcw->page)) {
> > > +			page_check_walk_done(pcw);
> > > +			return false;
> > > +		}
> > > +	}
> > > +
> > > +	return __page_check_walk(pcw);
> > > +}
> > 
> > Was the decision to inline this a correct one?
> 
> Well, my logic was that in most cases we would have exactly one iteration.
> The only case when we need more than one iteration is PTE-mapped THP which
> is rare.
> I hoped to avoid additional function call. Not sure if it worth it.
> 
> Should I move it inside the function?

I suggest building a kernel with it uninlined, take a look at the bloat
factor then make a seat-of-the pants decision about "is it worth it". 
With quite a few callsites the saving from uninlining may be
significant.