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

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Message-ID: <20140207175622.GA14953@node.dhcp.inet.fi>
Date:	Fri, 7 Feb 2014 19:56:22 +0200
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Andi Kleen <ak@...ux.intel.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Anvin <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ning Qu <quning@...gle.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Matthew Wilcox <willy@...ux.intel.com>
Subject: Re: [RFC, PATCH] mm: map few pages around fault address if they are
 in page cache

On Fri, Feb 07, 2014 at 09:32:00AM -0800, Andi Kleen wrote:
> > I haven't tested it much, but my kvm boots. There're few places where code
> > should be fixed. __do_fault() and filemap_fault() are too ugly and need to
> > be cleaned.
> > 
> > I don't have any performance data yet.
> > 
> > Any thoughts?
> 
> It seems very drastic to do it unconditionally. How about at least a simple
> stream detection heuristic and perhaps also madvise?

We already have readahead here it can be reused here. But see below.

> There are some extreme cases where workloads could use a lot more memory
> than before, if they access their memory sparsely in the right pattern.

Have you noticied that we don't actually allocate any memory: only reuse
what's already there. Sure, it will increase VmSize, but do we care?

-- 
 Kirill A. Shutemov
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