Re: [RFC 05/11] mm: make the try_to_munlock void function

From: Minchan Kim <minchan@kernel.org>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Andrew Morton <akpm@linux-foundation.org>, <kernel-team@lge.com>,
	<linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Michal Hocko <mhocko@suse.com>, Vlastimil Babka <vbabka@suse.cz>,
	"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [RFC 05/11] mm: make the try_to_munlock void function
Date: Wed, 8 Mar 2017 15:41:47 +0900	[thread overview]
Message-ID: <20170308064147.GG11206@bbox> (raw)
In-Reply-To: <20170307151747.GA2940@node.shutemov.name>

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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