From: Minchan Kim <minchan@kernel.org>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Mel Gorman <mgorman@suse.de>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
kernel-team@fb.com
Subject: Re: [PATCH 5/5] mm: vmscan: move dirty pages out of the way until they're flushed
Date: Thu, 26 Jan 2017 10:47:36 +0900 [thread overview]
Message-ID: <20170126014736.GE21211@bbox> (raw)
In-Reply-To: <20170123181641.23938-6-hannes@cmpxchg.org>
On Mon, Jan 23, 2017 at 01:16:41PM -0500, Johannes Weiner wrote:
> We noticed a performance regression when moving hadoop workloads from
> 3.10 kernels to 4.0 and 4.6. This is accompanied by increased pageout
> activity initiated by kswapd as well as frequent bursts of allocation
> stalls and direct reclaim scans. Even lowering the dirty ratios to the
> equivalent of less than 1% of memory would not eliminate the issue,
> suggesting that dirty pages concentrate where the scanner is looking.
>
> This can be traced back to recent efforts of thrash avoidance. Where
> 3.10 would not detect refaulting pages and continuously supply clean
> cache to the inactive list, a thrashing workload on 4.0+ will detect
> and activate refaulting pages right away, distilling used-once pages
> on the inactive list much more effectively. This is by design, and it
> makes sense for clean cache. But for the most part our workload's
> cache faults are refaults and its use-once cache is from streaming
> writes. We end up with most of the inactive list dirty, and we don't
> go after the active cache as long as we have use-once pages around.
>
> But waiting for writes to avoid reclaiming clean cache that *might*
> refault is a bad trade-off. Even if the refaults happen, reads are
> faster than writes. Before getting bogged down on writeback, reclaim
> should first look at *all* cache in the system, even active cache.
>
> To accomplish this, activate pages that have been dirty or under
> writeback for two inactive LRU cycles. We know at this point that
> there are not enough clean inactive pages left to satisfy memory
> demand in the system. The pages are marked for immediate reclaim,
> meaning they'll get moved back to the inactive LRU tail as soon as
> they're written back and become reclaimable. But in the meantime, by
> reducing the inactive list to only immediately reclaimable pages, we
> allow the scanner to deactivate and refill the inactive list with
> clean cache from the active list tail to guarantee forward progress.
>
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Every patches look reasaonable to me.
next prev parent reply other threads:[~2017-01-26 1:47 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-23 18:16 [PATCH 0/5] mm: vmscan: fix kswapd writeback regression Johannes Weiner
2017-01-23 18:16 ` [PATCH 1/5] mm: vmscan: scan dirty pages even in laptop mode Johannes Weiner
2017-01-26 1:27 ` Minchan Kim
2017-01-26 9:52 ` Mel Gorman
2017-01-26 13:13 ` Michal Hocko
2017-01-23 18:16 ` [PATCH 2/5] mm: vmscan: kick flushers when we encounter dirty pages on the LRU Johannes Weiner
2017-01-26 1:35 ` Minchan Kim
2017-01-26 9:57 ` Mel Gorman
2017-01-26 17:47 ` Johannes Weiner
2017-01-26 18:47 ` Mel Gorman
2017-01-26 13:16 ` Michal Hocko
2017-01-23 18:16 ` [PATCH 3/5] mm: vmscan: remove old flusher wakeup from direct reclaim path Johannes Weiner
2017-01-26 1:38 ` Minchan Kim
2017-01-26 10:05 ` Mel Gorman
2017-01-26 18:50 ` Johannes Weiner
2017-01-26 20:45 ` Mel Gorman
2017-01-27 12:01 ` Michal Hocko
2017-01-27 14:27 ` Mel Gorman
2017-01-26 13:21 ` Michal Hocko
2017-01-23 18:16 ` [PATCH 4/5] mm: vmscan: only write dirty pages that the scanner has seen twice Johannes Weiner
2017-01-26 1:42 ` Minchan Kim
2017-01-26 10:08 ` Mel Gorman
2017-01-26 13:29 ` Michal Hocko
2017-01-23 18:16 ` [PATCH 5/5] mm: vmscan: move dirty pages out of the way until they're flushed Johannes Weiner
2017-01-26 1:47 ` Minchan Kim [this message]
2017-01-26 10:19 ` Mel Gorman
2017-01-26 20:07 ` Johannes Weiner
2017-01-26 20:58 ` Mel Gorman
2017-01-26 13:52 ` Michal Hocko
2017-01-26 5:44 ` [PATCH 0/5] mm: vmscan: fix kswapd writeback regression Hillf Danton
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