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: Fri, 09 Oct 2020 10:38:22 -0400 [thread overview]
Message-ID: <82a7690e181cf1995e733120dad828e628cb80d9.camel@surriel.com> (raw)
In-Reply-To: <8b68bf5f6b041a75a62a1908214279a45722dda6.camel@surriel.com>
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On Mon, 2020-10-05 at 13:32 -0400, Rik van Riel wrote:
> 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:
> > 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%.
Never mind that. On larger tests the effect seems to disappear,
probably because the logic in __swapin_nr_pages() already reduces
the number of pages read ahead to 2 on workloads with lots of
random access.
That reduces the latency effects observed.
Now we might
still see some memory waste due to decompressing
pages we don't need, but I have not seen any real effects from
that yet, either.
I think it may be time to focus on a larger memory waste with
zswap: leaving the compressed copy of memory around when we
decompress the memory at swapin time. More aggressively freeing
the compressed memory will probably buy us more than reducing
readahead.
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prev parent reply other threads:[~2020-10-09 14:38 UTC|newest]
Thread overview: 10+ 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
2020-09-22 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
2020-10-09 14:38 ` Rik van Riel [this message]
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