From: Andrew Morton <akpm@linux-foundation.org>
To: Mel Gorman <mel@csn.ul.ie>
Cc: Simon Kirby <sim@hostway.ca>,
KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
Shaohua Li <shaohua.li@intel.com>,
Dave Hansen <dave@linux.vnet.ibm.com>,
Johannes Weiner <hannes@cmpxchg.org>,
linux-mm <linux-mm@kvack.org>,
linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/6] mm: kswapd: Stop high-order balancing when any suitable zone is balanced
Date: Tue, 14 Dec 2010 14:33:06 -0800 [thread overview]
Message-ID: <20101214143306.485f2c7c.akpm@linux-foundation.org> (raw)
In-Reply-To: <1291995985-5913-2-git-send-email-mel@csn.ul.ie>
On Fri, 10 Dec 2010 15:46:20 +0000
Mel Gorman <mel@csn.ul.ie> wrote:
> When the allocator enters its slow path, kswapd is woken up to balance the
> node. It continues working until all zones within the node are balanced. For
> order-0 allocations, this makes perfect sense but for higher orders it can
> have unintended side-effects. If the zone sizes are imbalanced, kswapd may
> reclaim heavily within a smaller zone discarding an excessive number of
> pages.
Why was it doing this?
> The user-visible behaviour is that kswapd is awake and reclaiming
> even though plenty of pages are free from a suitable zone.
Suitable for what? I assume you refer to a future allocation which can
be satisfied from more than one of the zones?
But what if that allocation wanted to allocate a high-order page from
a zone which we just abandoned?
> This patch alters the "balance" logic for high-order reclaim allowing kswapd
> to stop if any suitable zone becomes balanced to reduce the number of pages
again, suitable for what?
> it reclaims from other zones. kswapd still tries to ensure that order-0
> watermarks for all zones are met before sleeping.
Handling order-0 pages differently from higher-order pages sounds weird
and wrong.
I don't think I understand this patch.
WARNING: multiple messages have this Message-ID (diff)
From: Andrew Morton <akpm@linux-foundation.org>
To: Mel Gorman <mel@csn.ul.ie>
Cc: Simon Kirby <sim@hostway.ca>,
KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
Shaohua Li <shaohua.li@intel.com>,
Dave Hansen <dave@linux.vnet.ibm.com>,
Johannes Weiner <hannes@cmpxchg.org>,
linux-mm <linux-mm@kvack.org>,
linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/6] mm: kswapd: Stop high-order balancing when any suitable zone is balanced
Date: Tue, 14 Dec 2010 14:33:06 -0800 [thread overview]
Message-ID: <20101214143306.485f2c7c.akpm@linux-foundation.org> (raw)
In-Reply-To: <1291995985-5913-2-git-send-email-mel@csn.ul.ie>
On Fri, 10 Dec 2010 15:46:20 +0000
Mel Gorman <mel@csn.ul.ie> wrote:
> When the allocator enters its slow path, kswapd is woken up to balance the
> node. It continues working until all zones within the node are balanced. For
> order-0 allocations, this makes perfect sense but for higher orders it can
> have unintended side-effects. If the zone sizes are imbalanced, kswapd may
> reclaim heavily within a smaller zone discarding an excessive number of
> pages.
Why was it doing this?
> The user-visible behaviour is that kswapd is awake and reclaiming
> even though plenty of pages are free from a suitable zone.
Suitable for what? I assume you refer to a future allocation which can
be satisfied from more than one of the zones?
But what if that allocation wanted to allocate a high-order page from
a zone which we just abandoned?
> This patch alters the "balance" logic for high-order reclaim allowing kswapd
> to stop if any suitable zone becomes balanced to reduce the number of pages
again, suitable for what?
> it reclaims from other zones. kswapd still tries to ensure that order-0
> watermarks for all zones are met before sleeping.
Handling order-0 pages differently from higher-order pages sounds weird
and wrong.
I don't think I understand this patch.
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next prev parent reply other threads:[~2010-12-14 22:33 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-12-10 15:46 [PATCH 0/6] Prevent kswapd dumping excessive amounts of memory in response to high-order allocations V4 Mel Gorman
2010-12-10 15:46 ` Mel Gorman
2010-12-10 15:46 ` [PATCH 1/6] mm: kswapd: Stop high-order balancing when any suitable zone is balanced Mel Gorman
2010-12-10 15:46 ` Mel Gorman
2010-12-13 19:34 ` Eric B Munson
2010-12-14 22:33 ` Andrew Morton [this message]
2010-12-14 22:33 ` Andrew Morton
2010-12-15 10:42 ` Mel Gorman
2010-12-15 10:42 ` Mel Gorman
2010-12-10 15:46 ` [PATCH 2/6] mm: kswapd: Keep kswapd awake for high-order allocations until a percentage of the node " Mel Gorman
2010-12-10 15:46 ` Mel Gorman
2010-12-13 2:03 ` KAMEZAWA Hiroyuki
2010-12-13 2:03 ` KAMEZAWA Hiroyuki
2010-12-13 19:37 ` Eric B Munson
2010-12-14 22:43 ` Andrew Morton
2010-12-14 22:43 ` Andrew Morton
2010-12-15 10:54 ` Mel Gorman
2010-12-15 10:54 ` Mel Gorman
2010-12-10 15:46 ` [PATCH 3/6] mm: kswapd: Use the order that kswapd was reclaiming at for sleeping_prematurely() Mel Gorman
2010-12-10 15:46 ` Mel Gorman
2010-12-13 19:38 ` Eric B Munson
2010-12-10 15:46 ` [PATCH 4/6] mm: kswapd: Reset kswapd_max_order and classzone_idx after reading Mel Gorman
2010-12-10 15:46 ` Mel Gorman
2010-12-13 19:39 ` Eric B Munson
2010-12-10 15:46 ` [PATCH 5/6] mm: kswapd: Treat zone->all_unreclaimable in sleeping_prematurely similar to balance_pgdat() Mel Gorman
2010-12-10 15:46 ` Mel Gorman
2010-12-13 19:40 ` Eric B Munson
2010-12-10 15:46 ` [PATCH 6/6] mm: kswapd: Use the classzone idx that kswapd was using for sleeping_prematurely() Mel Gorman
2010-12-10 15:46 ` Mel Gorman
2010-12-13 19:43 ` Eric B Munson
-- strict thread matches above, loose matches on Subject: below --
2010-12-09 11:18 [PATCH 0/5] Prevent kswapd dumping excessive amounts of memory in response to high-order allocations V3 Mel Gorman
2010-12-09 11:18 ` [PATCH 1/6] mm: kswapd: Stop high-order balancing when any suitable zone is balanced Mel Gorman
2010-12-09 11:18 ` Mel Gorman
2010-12-09 15:21 ` Minchan Kim
2010-12-09 15:21 ` Minchan Kim
2010-12-10 1:06 ` KAMEZAWA Hiroyuki
2010-12-10 1:06 ` KAMEZAWA Hiroyuki
2010-12-13 16:54 ` Eric B Munson
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