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

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Date:   Tue, 7 Mar 2017 18:17:47 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Minchan Kim <minchan@...nel.org>
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 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().

Otherwise looks good to me.

Will free adding my Acked-by once this nit is addressed.

-- 
 Kirill A. Shutemov