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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: Tue, 30 Aug 2016 10:39:55 +0100	[thread overview]
Message-ID: <20160830093955.GV2693@suse.de> (raw)
In-Reply-To: <alpine.DEB.2.20.1608251451070.10766@east.gentwo.org>

On Thu, Aug 25, 2016 at 02:55:43PM -0500, Christoph Lameter wrote:
> On Thu, 25 Aug 2016, Mel Gorman wrote:
> 
> > 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.
> 
> Userspace mapped pages can be hugepages as well as giant pages and that
> has been there for a long time. Intermediate sizes would be useful too in
> order to avoid having to keep lists of 4k pages around and continually
> scan them.
> 

Userspace pages cannot always be mapped as huge or giant. mprotect on a
4K boundary is an obvious example.

> > 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.
> 
> Huge pages cannot be dirtied?

I didn't say that, I said they are required to avoid IO multiplier
effects. If a file is mapped as 2M or 1G then even a 1 byte write requires
2M or 1G of IO to writeback.

> This is an issue of hardware support. On
> x867 you only have one size. I am pretty such that even intel would
> support other sizes if needed. The case has been repeatedly made that 64k
> pages f.e. would be useful to have on x86.
> 

64K pages are not a universal win even on the arches that do support them.

-- 
Mel Gorman
SUSE Labs

  parent reply	other threads:[~2016-08-30  9:40 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
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               ` Mel Gorman [this message]
2016-08-30 19:32                 ` what is the purpose of SLAB and SLUB (was: Re: [PATCH v3] mm/slab: Improve performance of gathering slabinfo) stats Christoph Lameter

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