linux-kernel - Re: [PATCH 2/3] mm: calculate deferred pages after skipping mirrored memory

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Date:   Wed, 25 Jul 2018 09:32:31 -0400
From:   Pavel Tatashin <pasha.tatashin@...cle.com>
To:     osalvador@...hadventures.net
Cc:     Steven Sistare <steven.sistare@...cle.com>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        kirill.shutemov@...ux.intel.com, Michal Hocko <mhocko@...e.com>,
        Linux Memory Management List <linux-mm@...ck.org>,
        dan.j.williams@...el.com, jack@...e.cz, jglisse@...hat.com,
        Souptick Joarder <jrdr.linux@...il.com>, bhe@...hat.com,
        gregkh@...uxfoundation.org, Vlastimil Babka <vbabka@...e.cz>,
        Wei Yang <richard.weiyang@...il.com>, dave.hansen@...el.com,
        rientjes@...gle.com, mingo@...nel.org, abdhalee@...ux.vnet.ibm.com,
        mpe@...erman.id.au
Subject: Re: [PATCH 2/3] mm: calculate deferred pages after skipping mirrored memory

On Wed, Jul 25, 2018 at 8:15 AM Oscar Salvador
<osalvador@...hadventures.net> wrote:
>
> On Tue, Jul 24, 2018 at 07:55:19PM -0400, Pavel Tatashin wrote:
> > update_defer_init() should be called only when struct page is about to be
> > initialized. Because it counts number of initialized struct pages, but
> > there we may skip struct pages if there is some mirrored memory.
> >
> > So move, update_defer_init() after checking for mirrored memory.
> >
> > Also, rename update_defer_init() to defer_init() and reverse the return
> > boolean to emphasize that this is a boolean function, that tells that the
> > reset of memmap initialization should be deferred.
> >
> > Make this function self-contained: do not pass number of already
> > initialized pages in this zone by using static counters.
> >
> > Signed-off-by: Pavel Tatashin <pasha.tatashin@...cle.com>
> > ---
> >  mm/page_alloc.c | 40 ++++++++++++++++++++--------------------
> >  1 file changed, 20 insertions(+), 20 deletions(-)
> >
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index cea749b26394..86c678cec6bd 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -306,24 +306,28 @@ static inline bool __meminit early_page_uninitialised(unsigned long pfn)
> >  }
> >
> >  /*
> > - * Returns false when the remaining initialisation should be deferred until
> > + * Returns true when the remaining initialisation should be deferred until
> >   * later in the boot cycle when it can be parallelised.
> >   */
> > -static inline bool update_defer_init(pg_data_t *pgdat,
> > -                             unsigned long pfn, unsigned long zone_end,
> > -                             unsigned long *nr_initialised)
> > +static inline bool defer_init(int nid, unsigned long pfn, unsigned long end_pfn)
> >  {
> > +     static unsigned long prev_end_pfn, nr_initialised;
> > +
> > +     if (prev_end_pfn != end_pfn) {
> > +             prev_end_pfn = end_pfn;
> > +             nr_initialised = 0;
> > +     }
> Hi Pavel,
>
> What about a comment explaining that "if".
> I am not the brightest one, so it took me a bit to figure out that we got that "if" there
> because now that the variables are static, we need to somehow track whenever we change to
> another zone.

Hi Oscar,

Hm, yeah a comment would be appropriate here. I will send an updated
patch. I will also change the functions from inline to normal
functions as Andrew pointed out: it is not a good idea to use statics
in inline functions.

Thank you,
Pavel