linux-kernel - Re: [PATCH 1/2] mm/vmalloc: Add interfaces to free unused page table

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Date:   Thu, 8 Mar 2018 15:56:30 +0000
From:   "Kani, Toshi" <toshi.kani@....com>
To:     "willy@...radead.org" <willy@...radead.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "bp@...e.de" <bp@...e.de>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "guohanjun@...wei.com" <guohanjun@...wei.com>,
        "wxf.wang@...ilicon.com" <wxf.wang@...ilicon.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "hpa@...or.com" <hpa@...or.com>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "will.deacon@....com" <will.deacon@....com>,
        "Hocko, Michal" <mhocko@...e.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/2] mm/vmalloc: Add interfaces to free unused page table

On Wed, 2018-03-07 at 20:00 -0800, Matthew Wilcox wrote:
> On Wed, Mar 07, 2018 at 11:32:26AM -0700, Toshi Kani wrote:
> > +/**
> > + * pud_free_pmd_page - clear pud entry and free pmd page
> > + *
> > + * Returns 1 on success and 0 on failure (pud not cleared).
> > + */
> > +int pud_free_pmd_page(pud_t *pud)
> > +{
> > +	return pud_none(*pud);
> > +}
> 
> Wouldn't it be clearer if you returned 'bool' instead of 'int' here?

I thought about it and decided to use 'int' since all other pud/pmd/pte
interfaces, such as pud_none() above, use 'int'.

> Also you didn't document the pud parameter, nor use the approved form
> for documenting the return type, nor the calling context.  So I would
> have written it out like this:
> 
> /**
>  * pud_free_pmd_page - Clear pud entry and free pmd page.
>  * @pud: Pointer to a PUD.
>  *
>  * Context: Caller should hold mmap_sem write-locked.
>  * Return: %true if clearing the entry succeeded.
>  */

Will do.

Thanks!
-Toshi