linux-kernel - Re: [PATCH] mm/page_alloc: cleanup __alloc_pages_direct

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Date:   Mon, 19 Aug 2019 23:29:51 +0800
From:   Pengfei Li <lpf.vector@...il.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, mhocko@...e.com,
        osalvador@...e.de, pavel.tatashin@...rosoft.com,
        Mel Gorman <mgorman@...hsingularity.net>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/page_alloc: cleanup __alloc_pages_direct_compact()

On Mon, Aug 19, 2019 at 9:50 PM Vlastimil Babka <vbabka@...e.cz> wrote:
>
> On 8/17/19 12:51 PM, Pengfei Li wrote:
> > This patch cleans up the if(page).
> >
> > No functional change.
> >
> > Signed-off-by: Pengfei Li <lpf.vector@...il.com>
>
> I don't see much benefit here. The indentation wasn't that bad that it
> had to be reduced using goto. But the patch is not incorrect so I'm not
> NACKing.
>

Thanks for your review and comments.

This patch reduces the number of times the if(page)
(as the compiler does), and the downside is that there is a goto.

If this improves readability, accept it. Otherwise, leave it as it is.

Thanks again.

---
Pengfei


> > ---
> >  mm/page_alloc.c | 28 ++++++++++++++++------------
> >  1 file changed, 16 insertions(+), 12 deletions(-)
> >
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 272c6de1bf4e..51f056ac09f5 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -3890,6 +3890,7 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
> >               enum compact_priority prio, enum compact_result *compact_result)
> >  {
> >       struct page *page = NULL;
> > +     struct zone *zone;
> >       unsigned long pflags;
> >       unsigned int noreclaim_flag;
> >
> > @@ -3911,23 +3912,26 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
> >        */
> >       count_vm_event(COMPACTSTALL);
> >
> > -     /* Prep a captured page if available */
> > -     if (page)
> > +     if (page) {
> > +             /* Prep a captured page if available */
> >               prep_new_page(page, order, gfp_mask, alloc_flags);
> > -
> > -     /* Try get a page from the freelist if available */
> > -     if (!page)
> > +     } else {
> > +             /* Try get a page from the freelist if available */
> >               page = get_page_from_freelist(gfp_mask, order, alloc_flags, ac);
> >
> > -     if (page) {
> > -             struct zone *zone = page_zone(page);
> > -
> > -             zone->compact_blockskip_flush = false;
> > -             compaction_defer_reset(zone, order, true);
> > -             count_vm_event(COMPACTSUCCESS);
> > -             return page;
> > +             if (!page)
> > +                     goto failed;
> >       }
> >
> > +     zone = page_zone(page);
> > +     zone->compact_blockskip_flush = false;
> > +     compaction_defer_reset(zone, order, true);
> > +
> > +     count_vm_event(COMPACTSUCCESS);
> > +
> > +     return page;
> > +
> > +failed:
> >       /*
> >        * It's bad if compaction run occurs and fails. The most likely reason
> >        * is that pages exist, but not enough to satisfy watermarks.
> >
>