linux-kernel - Re: [PATCH 0/1] mm, shmem: map few pages around fault address if they are in page cache

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Message-Id: <20140228143440.e0ec026baeced2efbb52aa50@linux-foundation.org>
Date:	Fri, 28 Feb 2014 14:34:40 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Ning Qu <quning@...gle.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andi Kleen <ak@...ux.intel.com>,
	Matthew Wilcox <matthew.r.wilcox@...el.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Dave Chinner <david@...morbit.com>, Ning Qu <quning@...il.com>,
	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH 0/1] mm, shmem: map few pages around fault address if
 they are in page cache

On Fri, 28 Feb 2014 14:18:50 -0800 Ning Qu <quning@...gle.com> wrote:

> This is a follow-up patch for "mm: map few pages around fault address if they are in page cache"
> 
> We use the generic filemap_map_pages as ->map_pages in shmem/tmpfs.
> 

Please cc Hugh on shmem/tmpfs things

> 
> =========================================================================
> Below is just some simple experiment numbers from this patch, let me know if
> you would like more:
> 
> Tested on Xeon machine with 64GiB of RAM, using the current default fault
> order 4.
> 
> Sequential access 8GiB file
> 			Baseline 	with-patch
> 1 thread
>     minor fault		205		101	

Confused.  Sequential access of an 8G file should generate 2,000,000
minor faults, not 205.  And with FAULT_AROUND_ORDER=4, that should come
down to 2,000,000/16 minor faults when using faultaround?

>     time, seconds	7.94		7.82
> 
> Random access 8GiB file
> 			Baseline 	with-patch
> 1 thread
>     minor fault		724		623
>     time, seconds	9.75		9.84
> 

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