linux-kernel - Re: [PATCH] mm: create a separate slab for page->ptl allocation

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Date:	Tue, 22 Oct 2013 13:55:12 +0100
From:	Fengguang Wu <fengguang.wu@...el.com>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH] mm: create a separate slab for page->ptl allocation

On Tue, Oct 22, 2013 at 02:53:59PM +0300, Kirill A. Shutemov wrote:
> If DEBUG_SPINLOCK and DEBUG_LOCK_ALLOC are enabled spinlock_t on x86_64
> is 72 bytes. For page->ptl they will be allocated from kmalloc-96 slab,
> so we loose 24 on each. An average system can easily allocate few tens
> thousands of page->ptl and overhead is significant.
> 
> Let's create a separate slab for page->ptl allocation to solve this.

Tested-by: Fengguang Wu <fengguang.wu@...el.com>

In a 4p server, we noticed up to +469.1% increase in will-it-scale page_fault3
test case and +199.8% in vm-scalability case-shm-pread-seq-mt.

    5c02216ce3110aab070d      5a58baaa0a1af0a43d7c
------------------------  ------------------------  
               300409.00      +440.2%   1622770.80  TOTAL will-it-scale.page_fault3.90.threads

    5c02216ce3110aab070d      5a58baaa0a1af0a43d7c
------------------------  ------------------------  
               291257.80      +469.1%   1657582.20  TOTAL will-it-scale.page_fault3.120.threads

...

    5c02216ce3110aab070d      5a58baaa0a1af0a43d7c
------------------------  ------------------------  
              4034831.40      +199.8%  12095649.80  TOTAL vm-scalability.throughput

Thanks,
Fengguang
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