From: David Rientjes <rientjes@google.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Mel Gorman <mgorman@suse.de>, Joonsoo Kim <js1304@gmail.com>,
Vlastimil Babka <vbabka@suse.cz>,
Markus Trippelsdorf <markus@trippelsdorf.de>,
linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm: clarify COMPACTION Kconfig text
Date: Thu, 25 Aug 2016 15:34:54 -0700 (PDT) [thread overview]
Message-ID: <alpine.DEB.2.10.1608251524140.48031@chino.kir.corp.google.com> (raw)
In-Reply-To: <20160825065424.GA4230@dhcp22.suse.cz>
On Thu, 25 Aug 2016, Michal Hocko wrote:
> > I don't believe it has been an issue in the past for any archs that
> > don't use thp.
>
> Well, fragmentation is a real problem and order-0 reclaim will be never
> anywhere close to reliably provide higher order pages. Well, reclaiming
> a lot of memory can increase the probability of a success but that
> can quite often lead to over reclaim and long stalls. There are other
> sources of high order requests than THP so this is not about THP at all
> IMHO.
>
Would it be possible to list the high-order allocations you are concerned
about other than thp that doesn't have fallback behavior like skbuff and
slub allocations? struct task_struct is an order-1 allocation and there
may be order-1 slab bucket usage, but what is higher order or requires
aggressive compaction to allocate? Surely you're not suggesting that
order-0 reclaim cannot form order-1 memory. I am concerned about kernels
that require a small memory footprint and cannot enable all of
CONFIG_COMPACTION and CONFIG_MIGRATION. Embedded devices are not a
negligible minority of kernels.
> > , CONFIG_MIGRATION. Migration has a
> > dependency of NUMA or memory hot-remove (not all popular). Compaction can
> > defragment memory within single zone without reliance on NUMA.
>
> I am not sure I am following you here.
> MIGRATION depends on (NUMA || ARCH_ENABLE_MEMORY_HOTREMOVE || COMPACTION || CMA) && MMU
>
Embedded device may be UMA and not care for memory hotplug or failure
handling and rely solely on order-0 and order-1 memory.
WARNING: multiple messages have this Message-ID (diff)
From: David Rientjes <rientjes@google.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Mel Gorman <mgorman@suse.de>, Joonsoo Kim <js1304@gmail.com>,
Vlastimil Babka <vbabka@suse.cz>,
Markus Trippelsdorf <markus@trippelsdorf.de>,
linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm: clarify COMPACTION Kconfig text
Date: Thu, 25 Aug 2016 15:34:54 -0700 (PDT) [thread overview]
Message-ID: <alpine.DEB.2.10.1608251524140.48031@chino.kir.corp.google.com> (raw)
In-Reply-To: <20160825065424.GA4230@dhcp22.suse.cz>
On Thu, 25 Aug 2016, Michal Hocko wrote:
> > I don't believe it has been an issue in the past for any archs that
> > don't use thp.
>
> Well, fragmentation is a real problem and order-0 reclaim will be never
> anywhere close to reliably provide higher order pages. Well, reclaiming
> a lot of memory can increase the probability of a success but that
> can quite often lead to over reclaim and long stalls. There are other
> sources of high order requests than THP so this is not about THP at all
> IMHO.
>
Would it be possible to list the high-order allocations you are concerned
about other than thp that doesn't have fallback behavior like skbuff and
slub allocations? struct task_struct is an order-1 allocation and there
may be order-1 slab bucket usage, but what is higher order or requires
aggressive compaction to allocate? Surely you're not suggesting that
order-0 reclaim cannot form order-1 memory. I am concerned about kernels
that require a small memory footprint and cannot enable all of
CONFIG_COMPACTION and CONFIG_MIGRATION. Embedded devices are not a
negligible minority of kernels.
> > , CONFIG_MIGRATION. Migration has a
> > dependency of NUMA or memory hot-remove (not all popular). Compaction can
> > defragment memory within single zone without reliance on NUMA.
>
> I am not sure I am following you here.
> MIGRATION depends on (NUMA || ARCH_ENABLE_MEMORY_HOTREMOVE || COMPACTION || CMA) && MMU
>
Embedded device may be UMA and not care for memory hotplug or failure
handling and rely solely on order-0 and order-1 memory.
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next prev parent reply other threads:[~2016-08-25 22:43 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-23 8:09 [PATCH] mm: clarify COMPACTION Kconfig text Michal Hocko
2016-08-23 8:09 ` Michal Hocko
2016-08-23 8:38 ` Markus Trippelsdorf
2016-08-23 8:38 ` Markus Trippelsdorf
2016-08-23 9:17 ` Michal Hocko
2016-08-23 9:17 ` Michal Hocko
2016-08-25 0:54 ` David Rientjes
2016-08-25 0:54 ` David Rientjes
2016-08-25 6:54 ` Michal Hocko
2016-08-25 6:54 ` Michal Hocko
2016-08-25 22:34 ` David Rientjes [this message]
2016-08-25 22:34 ` David Rientjes
2016-08-26 6:44 ` Michal Hocko
2016-08-26 6:44 ` Michal Hocko
2016-08-29 14:10 ` Johannes Weiner
2016-08-29 14:10 ` Johannes Weiner
2016-08-29 14:50 ` Michal Hocko
2016-08-29 14:50 ` Michal Hocko
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