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Date: Tue, 15 Mar 2016 18:42:58 +0300
From: "Kirill A. Shutemov" <kirill@shutemov.name>
Subject: Re: [PATCH] thp, mlock: update unevictable-lru.txt
Message-ID: <20160315154258.GB16462@node.shutemov.name>
References: <1458053744-40664-1-git-send-email-kirill.shutemov@linux.intel.com>
 <56E82AAE.8090003@intel.com>
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To: Dave Hansen <dave.hansen@intel.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org

On Tue, Mar 15, 2016 at 08:30:54AM -0700, Dave Hansen wrote:
> On 03/15/2016 07:55 AM, Kirill A. Shutemov wrote:
> > +Transparent huge page is represented by single entry on a lru list and
> > +therefore we can only make unevictable entire compound page, not
> > +individual subpages.
> 
> A few grammar nits:
> 
> A transparent huge page is represented by a single entry on an lru list.
> Therefore, we can only make unevictable an entire compound page, not
> individual subpages.

Thanks.

> > +We handle this by forbidding mlocking PTE-mapped huge pages. This way we
> > +keep the huge page accessible for vmscan. Under memory pressure the page
> > +will be split, subpages from VM_LOCKED VMAs moved to unevictable lru and
> > +the rest can be evicted.
> 
> What do you mean by "mlocking" in this context?  Do you mean that we
> actually return -ESOMETHING from mlock() on PTE-mapped huge pages?  Or,
> do you just mean that we defer treating PTE-mapped huge pages as
> PageUnevictable() inside the kernel?

The latter.

> I think we should probably avoid saying "mlocking" when we really mean
> "kernel-internal mlocked page handling" aka. the unevictable list.

What about

"We handle this by keeping PTE-mapped huge pages on normal LRU lists."

?

The updated patch is below.