linux-kernel - Re: [PATCH 2/6] mm: hugetlb_vmemmap: optimize vmemmap_optimize

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Date:   Mon, 13 Jun 2022 16:24:01 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     Oscar Salvador <osalvador@...e.de>
Cc:     mike.kravetz@...cle.com, david@...hat.com,
        akpm@...ux-foundation.org, corbet@....net, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH 2/6] mm: hugetlb_vmemmap: optimize vmemmap_optimize_mode
 handling

On Mon, Jun 13, 2022 at 10:10:08AM +0200, Oscar Salvador wrote:
> On Mon, Jun 13, 2022 at 02:35:08PM +0800, Muchun Song wrote:
> > We hold an another reference to hugetlb_optimize_vmemmap_key when
> > making vmemmap_optimize_mode on, because we use static_key to tell
> > memory_hotplug that memory_hotplug.memmap_on_memory should be
> > overridden.  However, this rule has gone when we have introduced
> > SECTION_CANNOT_OPTIMIZE_VMEMMAP.  Therefore, we could simplify
> > vmemmap_optimize_mode handling by not holding an another reference
> > to hugetlb_optimize_vmemmap_key.
> > 
> > Signed-off-by: Muchun Song <songmuchun@...edance.com>
> 
> LGTM, and it looks way nicer, so
> 
> Reviewed-by: Oscar Salvador <osalvador@...e.de>
>

Thanks for taking a look.
 
> One question below though
> 
> > -static enum vmemmap_optimize_mode vmemmap_optimize_mode =
> > +static bool vmemmap_optimize_enabled =
> >  	IS_ENABLED(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON);
> 
> So, by default vmemmap_optimize_enabled will be on if we have
> CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON, but we can always override that
> via cmdline, as below, right?
> 

Totally right. CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON only control
if the feature is enabled by default when the users do not specify "it should
be off" via cmdline. 

Thanks.