linux-kernel - Re: [PATCH v5 4/4] hugetlb: allow to free gigantic pages regardless of the configuration

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Date:   Wed, 6 Mar 2019 13:17:38 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Alex Ghiti <alex@...ti.fr>, Vlastimil Babka <vbabka@...e.cz>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        "David S . Miller" <davem@...emloft.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
        linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH v5 4/4] hugetlb: allow to free gigantic pages regardless
 of the configuration

On 3/6/19 12:08 PM, Alex Ghiti wrote:
>>>
>>> +    /*
>>> +     * Gigantic pages allocation depends on the capability for large
>>> page
>>> +     * range allocation. If the system cannot provide
>>> alloc_contig_range,
>>> +     * allow users to free gigantic pages.
>>> +     */
>>> +    if (hstate_is_gigantic(h) && !IS_ENABLED(CONFIG_CONTIG_ALLOC)) {
>>> +        spin_lock(&hugetlb_lock);
>>> +        if (count > persistent_huge_pages(h)) {
>>> +            spin_unlock(&hugetlb_lock);
>>> +            return -EINVAL;
>>> +        }
>>> +        goto decrease_pool;
>>> +    }
>> We talked about it during the last round and I don't seen any mention of
>> it here in comments or the changelog: Why is this a goto?  Why don't we
>> just let the code fall through to the "decrease_pool" label?  Why is
>> this new block needed at all?  Can't we just remove the old check and
>> let it be?
> 
> I'll get rid of the goto, I don't know how to justify it properly in a
> comment,
> maybe because it is not necessary.
> This is not a new block, this means exactly the same as before (remember
> gigantic_page_supported() actually meant CONTIG_ALLOC before this series),
> except that now we allow a user to free boottime allocated gigantic pages.
> And no we cannot just remove the check and let it be since it would modify
> the current behaviour, which is to return an error when trying to allocate
> gigantic pages whereas alloc_contig_range is not defined. I thought it was
> clearly commented above, I can try to make it more explicit.

OK, that makes sense.  Could you get some of this in the changelog,
please?  Otherwise this all looks good to me.