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From: Mel Gorman <mgorman@suse.de>
To: Christoph Lameter <cl@linux.com>
Cc: Michal Hocko <mhocko@kernel.org>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	Aruna Ramakrishna <aruna.ramakrishna@oracle.com>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Pekka Enberg <penberg@kernel.org>,
	David Rientjes <rientjes@google.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Jiri Slaby <jslaby@suse.cz>
Subject: Re: what is the purpose of SLAB and SLUB (was: Re: [PATCH v3] mm/slab: Improve performance of gathering slabinfo) stats
Date: Thu, 25 Aug 2016 11:07:07 +0100	[thread overview]
Message-ID: <20160825100707.GU2693@suse.de> (raw)
In-Reply-To: <alpine.DEB.2.20.1608242240460.1837@east.gentwo.org>

On Wed, Aug 24, 2016 at 11:01:43PM -0500, Christoph Lameter wrote:
> On Wed, 24 Aug 2016, Mel Gorman wrote:
> > If/when I get back to the page allocator, the priority would be a bulk
> > API for faster allocs of batches of order-0 pages instead of allocating
> > a large page and splitting.
> >
> 
> OMG. Do we really want to continue this? There are billions of Linux
> devices out there that require a reboot at least once a week. This is now
> standard with certain Android phones. In our company we reboot all
> machines every week because fragmentation degrades performance
> significantly. We need to finally face up to it and deal with the issue
> instead of continuing to produce more half ass-ed solutions.
> 

Flipping the lid aside, there will always be a need for fast management
of 4K pages. The primary use case is networking that sometimes uses
high-order pages to avoid allocator overhead and amortise DMA setup.
Userspace-mapped pages will always be 4K although fault-around may benefit
from bulk allocating the pages. That is relatively low hanging fruit that
would take a few weeks given a free schedule.

Dirty tracking of pages on a 4K boundary will always be required to avoid IO
multiplier effects that cannot be side-stepped by increasing the fundamental
unit of allocation.

Batching of tree_lock during reclaim for large files and swapping is also
relatively low hanging fruit that also is doable in a week or two.

A high-order per-cpu cache for SLUB to reduce zone->lock contention is
also relatively low hanging fruit with the caveat it makes per_cpu_pages
larger than a cache line.

If you want to rework the VM to use a larger fundamental unit, track
sub-units where required and deal with the internal fragmentation issues
then by all means go ahead and deal with it.
 
-- 
Mel Gorman
SUSE Labs

  reply	other threads:[~2016-08-25 10:08 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-08-17 18:20 [PATCH v3] mm/slab: Improve performance of gathering slabinfo stats Aruna Ramakrishna
2016-08-17 19:03 ` Eric Dumazet
2016-08-17 19:25   ` Aruna Ramakrishna
2016-08-18 11:52 ` Michal Hocko
2016-08-19  5:47   ` aruna.ramakrishna
2016-08-23  2:13   ` Joonsoo Kim
2016-08-23 15:38     ` what is the purpose of SLAB and SLUB (was: Re: [PATCH v3] mm/slab: Improve performance of gathering slabinfo) stats Michal Hocko
2016-08-23 15:54       ` what is the purpose of SLAB and SLUB Andi Kleen
2016-08-25  4:10         ` Christoph Lameter
2016-08-25  7:32           ` Michal Hocko
2016-08-25 19:49             ` Christoph Lameter
2016-08-24  1:15       ` what is the purpose of SLAB and SLUB (was: Re: [PATCH v3] mm/slab: Improve performance of gathering slabinfo) stats Joonsoo Kim
2016-08-24  8:05         ` Michal Hocko
2016-08-24  8:20       ` Mel Gorman
2016-08-25  4:01         ` Christoph Lameter
2016-08-25 10:07           ` Mel Gorman [this message]
2016-08-25 19:55             ` Christoph Lameter
2016-08-26 20:47               ` what is the purpose of SLAB and SLUB Andi Kleen
2016-08-29 13:44                 ` Michal Hocko
2016-08-29 14:49                   ` Christoph Lameter
2016-08-30  9:39               ` what is the purpose of SLAB and SLUB (was: Re: [PATCH v3] mm/slab: Improve performance of gathering slabinfo) stats Mel Gorman
2016-08-30 19:32                 ` Christoph Lameter

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