From: Rik van Riel <riel@surriel.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
kernel-team@fb.com, niketa@fb.com, sjenning@redhat.com,
ddstreet@ieee.org, konrad.wilk@oracle.com, hannes@cmpxchg.org
Subject: Re: [PATCH 0/2] mm,swap: skip swap readahead for instant IO (like zswap)
Date: Mon, 05 Oct 2020 13:32:58 -0400 [thread overview]
Message-ID: <8b68bf5f6b041a75a62a1908214279a45722dda6.camel@surriel.com> (raw)
In-Reply-To: <20200922101250.527d9e676fefbb4c8d0cd5b9@linux-foundation.org>
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On Tue, 2020-09-22 at 10:12 -0700, Andrew Morton wrote:
> On Mon, 21 Sep 2020 22:01:46 -0400 Rik van Riel <riel@surriel.com>
> wrote:
>
> > Both with frontswap/zswap, and with some extremely fast IO devices,
> > swap IO will be done before the "asynchronous" swap_readpage() call
> > has returned.
> >
> > In that case, doing swap readahead only wastes memory, increases
> > latency, and increases the chances of needing to evict something
> > more
> > useful from memory. In that case, just skip swap readahead.
>
> Any quantitative testing results?
I have test results with a real workload now.
Without this patch, enabling zswap results in about an
8% increase in p99 request latency. With these patches,
the latency penalty for enabling zswap is under 1%.
Enabling zswap
allows us to give the main workload a
little more memory, since the spikes in memory demand
caused by things like system management software no
longer cause large latency issues.
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next prev parent reply other threads:[~2020-10-05 17:33 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-22 2:01 [PATCH 0/2] mm,swap: skip swap readahead for instant IO (like zswap) Rik van Riel
2020-09-22 2:01 ` [PATCH 1/2] mm,swap: extract swap single page readahead into its own function Rik van Riel
2020-09-23 6:32 ` Christoph Hellwig
2020-09-23 8:02 ` Hillf Danton
2020-09-22 2:01 ` [PATCH 2/2] mm,swap: skip swap readahead if page was obtained instantaneously Rik van Riel
2020-09-22 3:13 ` huang ying
2020-09-22 11:33 ` Rik van Riel
2020-09-23 6:35 ` Christoph Hellwig
2020-09-22 17:12 ` [PATCH 0/2] mm,swap: skip swap readahead for instant IO (like zswap) Andrew Morton
2020-10-05 17:32 ` Rik van Riel [this message]
2020-10-09 14:38 ` Rik van Riel
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