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From: Ivan Babrou <ivan@cloudflare.com>
To: linux-mm@kvack.org
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
	kernel-team <kernel-team@cloudflare.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Mel Gorman <mgorman@techsingularity.net>,
	Vlastimil Babka <vbabka@suse.cz>
Subject: Reclaim regression after 1c30844d2dfe
Date: Fri, 7 Feb 2020 14:54:43 -0800	[thread overview]
Message-ID: <CABWYdi1eOUD1DHORJxTsWPMT3BcZhz++xP1pXhT=x4SgxtgQZA@mail.gmail.com> (raw)

This change from 5.5 times:

* https://github.com/torvalds/linux/commit/1c30844d2dfe

> mm: reclaim small amounts of memory when an external fragmentation event occurs

Introduced undesired effects in our environment.

* NUMA with 2 x CPU
* 128GB of RAM
* THP disabled
* Upgraded from 4.19 to 5.4

Before we saw free memory hover at around 1.4GB with no spikes. After
the upgrade we saw some machines decide that they need a lot more than
that, with frequent spikes above 10GB, often only on a single numa
node.

We can see kswapd quite active in balance_pgdat (it didn't look like
it slept at all):

$ ps uax | fgrep kswapd
root       1850 23.0  0.0      0     0 ?        R    Jan30 1902:24 [kswapd0]
root       1851  1.8  0.0      0     0 ?        S    Jan30 152:16 [kswapd1]

This in turn massively increased pressure on page cache, which did not
go well to services that depend on having a quick response from a
local cache backed by solid storage.

Here's how it looked like when I zeroed vm.watermark_boost_factor:

* https://imgur.com/a/6IZWicU

IO subsided from 100% busy in page cache population at 300MB/s on a
single SATA drive down to under 100MB/s.

This sort of regression doesn't seem like a good thing.

             reply	other threads:[~2020-02-07 22:54 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-07 22:54 Ivan Babrou [this message]
2020-02-07 23:05 ` Reclaim regression after 1c30844d2dfe Rik van Riel
2020-02-08  9:08   ` Vlastimil Babka
2020-02-11 10:16 ` Mel Gorman
2020-02-12 22:45   ` Ivan Babrou
2020-02-12 23:55     ` Mel Gorman
2020-02-18 22:07       ` Ivan Babrou

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