linux-kernel - Re: [PATCH v9 03/12] mm: deferred_init

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Message-ID: <20171004084816.ljyw2gdf5gmgtm7z@dhcp22.suse.cz>
Date:   Wed, 4 Oct 2017 10:48:16 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Pasha Tatashin <pasha.tatashin@...cle.com>
Cc:     linux-kernel@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org,
        linux-s390@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        x86@...nel.org, kasan-dev@...glegroups.com, borntraeger@...ibm.com,
        heiko.carstens@...ibm.com, davem@...emloft.net,
        willy@...radead.org, ard.biesheuvel@...aro.org,
        mark.rutland@....com, will.deacon@....com, catalin.marinas@....com,
        sam@...nborg.org, mgorman@...hsingularity.net,
        steven.sistare@...cle.com, daniel.m.jordan@...cle.com,
        bob.picco@...cle.com
Subject: Re: [PATCH v9 03/12] mm: deferred_init_memmap improvements

On Tue 03-10-17 12:01:08, Pasha Tatashin wrote:
> Hi Michal,
> 
> Are you OK, if I replace DEFERRED_FREE() macro with a function like this:
> 
> /*
>  * Helper for deferred_init_range, free the given range, and reset the
>  * counters
>  */
> static inline unsigned long __def_free(unsigned long *nr_free,
>                                        unsigned long *free_base_pfn,
>                                        struct page **page)
> {
>         unsigned long nr = *nr_free;
> 
>         deferred_free_range(*free_base_pfn, nr);
>         *free_base_pfn = 0;
>         *nr_free = 0;
>         *page = NULL;
> 
>         return nr;
> }
> 
> Since it is inline, and we operate with non-volatile counters, compiler will
> be smart enough to remove all the unnecessary de-references. As a plus, we
> won't be adding any new branches, and the code is still going to stay
> compact.

OK. It is a bit clunky but we are holding too much state there. I
haven't checked whether that can be simplified but this can be always
done later.
-- 
Michal Hocko
SUSE Labs