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Date: Tue, 27 Sep 2016 02:11:32 +0300
From: "Kirill A. Shutemov" <kirill@shutemov.name>
Subject: Re: page_waitqueue() considered harmful
Message-ID: <20160926231132.GA17069@node.shutemov.name>
References: <CA+55aFwVSXZPONk2OEyxcP-aAQU7-aJsF3OFXVi8Z5vA11v_-Q@mail.gmail.com>
 <1474925009.17726.61.camel@redhat.com>
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To: Rik van Riel <riel@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>, Andrew Morton <akpm@linux-foundation.org>, "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, Johannes Weiner <hannes@cmpxchg.org>, Jan Kara <jack@suse.cz>, Mel Gorman <mgorman@techsingularity.net>, Peter Zijlstra <peterz@infradead.org>, linux-mm <linux-mm@kvack.org>

On Mon, Sep 26, 2016 at 05:23:29PM -0400, Rik van Riel wrote:
> On Mon, 2016-09-26 at 13:58 -0700, Linus Torvalds wrote:
> 
> > Is there really any reason for that incredible indirection? Do we
> > really want to make the page_waitqueue() be a per-zone thing at all?
> > Especially since all those wait-queues won't even be *used* unless
> > there is actual IO going on and people are really getting into
> > contention on the page lock.. Why isn't the page_waitqueue() just one
> > statically sized array?
> 
> Why are we touching file pages at all during fork()?

We are not.
Unless the vma has private pages (vma->anon_vma is not NULL).

See first lines for copy_page_range().

We probably can go futher and skip non-private pages within file VMA.
But we would need to touch struct page in this case, so it doesn't make
sense.

-- 
 Kirill A. Shutemov

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