linux-kernel - Re: [PATCH] mm: consolidate pgtable_cache_init() and pgd_cache

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Message-ID: <20190821163425.6jwxbvspjzqxysxc@willie-the-truck>
Date:   Wed, 21 Aug 2019 17:34:26 +0100
From:   Will Deacon <will@...nel.org>
To:     Mike Rapoport <rppt@...ux.ibm.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: consolidate pgtable_cache_init() and pgd_cache_init()

On Wed, Aug 21, 2019 at 07:01:59PM +0300, Mike Rapoport wrote:
> On Wed, Aug 21, 2019 at 04:49:42PM +0100, Will Deacon wrote:
> > On Wed, Aug 21, 2019 at 06:06:58PM +0300, Mike Rapoport wrote:
> > > diff --git a/init/main.c b/init/main.c
> > > index b90cb5f..2fa8038 100644
> > > --- a/init/main.c
> > > +++ b/init/main.c
> > > @@ -507,7 +507,7 @@ void __init __weak mem_encrypt_init(void) { }
> > >  
> > >  void __init __weak poking_init(void) { }
> > >  
> > > -void __init __weak pgd_cache_init(void) { }
> > > +void __init __weak pgtable_cache_init(void) { }
> > >  
> > >  bool initcall_debug;
> > >  core_param(initcall_debug, initcall_debug, bool, 0644);
> > > @@ -565,7 +565,6 @@ static void __init mm_init(void)
> > >  	init_espfix_bsp();
> > >  	/* Should be run after espfix64 is set up. */
> > >  	pti_init();
> > > -	pgd_cache_init();
> > >  }
> > 
> > AFAICT, this change means we now initialise our pgd cache before
> > debug_objects_mem_init() has run.
> 
> Right.
> 
> > Is that going to cause fireworks with CONFIG_DEBUG_OBJECTS when we later
> > free a pgd?
> 
> We don't allocate a pgd at that time, we only create the kmem cache for the
> future allocations. And that cache is never destroyed anyway.

Thanks for the explanation. In which case, for arm64:

Acked-by: Will Deacon <will@...nel.org>

Will