linux-kernel - Re: [PATCH v2 3/5] mm/page_alloc: Optimize free_area_init

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Message-ID: <20180719140327.GB10988@techadventures.net>
Date:   Thu, 19 Jul 2018 16:03:27 +0200
From:   Oscar Salvador <osalvador@...hadventures.net>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     akpm@...ux-foundation.org, pasha.tatashin@...cle.com,
        vbabka@...e.cz, aaron.lu@...el.com, iamjoonsoo.kim@....com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Oscar Salvador <osalvador@...e.de>
Subject: Re: [PATCH v2 3/5] mm/page_alloc: Optimize free_area_init_core

On Thu, Jul 19, 2018 at 03:44:17PM +0200, Michal Hocko wrote:
> On Thu 19-07-18 15:27:38, osalvador@...hadventures.net wrote:
> > From: Oscar Salvador <osalvador@...e.de>
> > 
> > In free_area_init_core we calculate the amount of managed pages
> > we are left with, by substracting the memmap pages and the pages
> > reserved for dma.
> > With the values left, we also account the total of kernel pages and
> > the total of pages.
> > 
> > Since memmap pages are calculated from zone->spanned_pages,
> > let us only do these calculcations whenever zone->spanned_pages is greather
> > than 0.
> 
> But why do we care? How do we test this? In other words, why is this
> worth merging?
 
Uhm, unless the values are going to be updated, why do we want to go through all
comparasions/checks?
I thought it was a nice thing to have the chance to skip that block unless we are going to
update the counters.

Again, if you think this only adds complexity and no good, I can drop it.

Thanks
-- 
Oscar Salvador
SUSE L3