linux-kernel - Re: [RFC 05/11] mm: make the try_to

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Date:   Wed, 8 Mar 2017 15:41:47 +0900
From:   Minchan Kim <minchan@...nel.org>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
CC:     Andrew Morton <akpm@...ux-foundation.org>, <kernel-team@....com>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [RFC 05/11] mm: make the try_to_munlock void function

On Tue, Mar 07, 2017 at 06:17:47PM +0300, Kirill A. Shutemov wrote:
> On Thu, Mar 02, 2017 at 03:39:19PM +0900, Minchan Kim wrote:
> > try_to_munlock returns SWAP_MLOCK if the one of VMAs mapped
> > the page has VM_LOCKED flag. In that time, VM set PG_mlocked to
> > the page if the page is not pte-mapped THP which cannot be
> > mlocked, either.
> > 
> > With that, __munlock_isolated_page can use PageMlocked to check
> > whether try_to_munlock is successful or not without relying on
> > try_to_munlock's retval. It helps to make ttu/ttuo simple with
> > upcoming patches.
> 
> I *think* you're correct, but it took time to wrap my head around.
> We basically rely on try_to_munlock() never caller for PTE-mapped THP.
> And we don't at the moment.
> 
> It worth adding something like
> 
> 	VM_BUG_ON_PAGE(PageCompound(page) && PageDoubleMap(page), page);
> 
> into try_to_munlock().

Agree.

> 
> Otherwise looks good to me.
> 
> Will free adding my Acked-by once this nit is addressed.

Thanks for the review this part, Kirill!

> 
> -- 
>  Kirill A. Shutemov
> 
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