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Date:   Thu, 7 Oct 2021 12:31:09 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc:     Mel Gorman <mgorman@techsingularity.net>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] mm: Optimise put_pages_list()
Message-Id: <20211007123109.6a49c7c625e414acf7546c89@linux-foundation.org>
In-Reply-To: <20211007192138.561673-1-willy@infradead.org>
References: <20211007192138.561673-1-willy@infradead.org>
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On Thu,  7 Oct 2021 20:21:37 +0100 "Matthew Wilcox (Oracle)" <willy@infradead.org> wrote:

> Instead of calling put_page() one page at a time, pop pages off
> the list if their refcount was too high and pass the remainder to
> put_unref_page_list().  This should be a speed improvement, but I have
> no measurements to support that.  Current callers do not care about
> performance, but I hope to add some which do.

Don't you think it would actually be slower to take an additional pass
across the list?  If the list is long enough to cause cache thrashing. 
Maybe it's faster for small lists.