From: Andrew Morton <akpm@linux-foundation.org>
To: David Rientjes <rientjes@google.com>
Cc: Bob Liu <lliubbo@gmail.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk,
mgorman@suse.de, hannes@cmpxchg.org, riel@redhat.com,
minchan@kernel.org, Bob Liu <bob.liu@oracle.com>
Subject: Re: [PATCH] mm: pagevec: cleanup: drop pvec->cold argument in all places
Date: Thu, 3 Oct 2013 14:10:08 -0700 [thread overview]
Message-ID: <20131003141008.0bf310445041a0919fe84fb9@linux-foundation.org> (raw)
In-Reply-To: <alpine.DEB.2.02.1310012243220.5682@chino.kir.corp.google.com>
On Tue, 1 Oct 2013 22:47:36 -0700 (PDT) David Rientjes <rientjes@google.com> wrote:
> On Mon, 30 Sep 2013, Andrew Morton wrote:
>
> > > Nobody uses the pvec->cold argument of pagevec and it's also unreasonable for
> > > pages in pagevec released as cold page, so drop the cold argument from pagevec.
> >
> > Is it unreasonable? I'd say it's unreasonable to assume that all pages
> > in all cases are likely to be cache-hot. Example: what if the pages
> > are being truncated and were found to be on the inactive LRU,
> > unreferenced?
> >
> > A useful exercise would be to go through all those pagevec_init() sites
> > and convince ourselves that the decision at each place was the correct
> > one.
> >
>
> Agreed, and the "cold" argument to release_pages() becomes a no-op if this
> patch is merged meaning that anything released through it will
> automatically go to the start of the pcp lists. If the pages aren't hot
> then this is exactly the opposite of what we wanted to do; the fact that
> the pvec length doesn't take into account the size of cpu cache can almost
> guarantee that everything isn't cache hot.
The hot/cold pages code was very marginal when we first merged it and I
suspect it has rotted since.
It would be a useful exercise for someone to disable it then run some
benchmarks with a view to removing it all. But the problem I have with
this approach is perhaps the code *could* become effective if some
careful maintenance work was done on it - we should at least get the
hot/cold decisions optimised before making a decision about the overall
desirability of keeping it.
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prev parent reply other threads:[~2013-10-03 21:10 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-09-28 8:33 [PATCH] mm: pagevec: cleanup: drop pvec->cold argument in all places Bob Liu
2013-09-30 22:02 ` Andrew Morton
2013-10-02 5:47 ` David Rientjes
2013-10-03 21:10 ` Andrew Morton [this message]
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