linux-kernel - Re: [PATCH v11 04/21] mm: Allow page fault handlers to perform the COW

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Date:	Sat, 18 Oct 2014 13:22:07 -0400
From:	Matthew Wilcox <willy@...ux.intel.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:	Matthew Wilcox <willy@...ux.intel.com>,
	Matthew Wilcox <matthew.r.wilcox@...el.com>,
	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v11 04/21] mm: Allow page fault handlers to perform the
 COW

On Fri, Oct 17, 2014 at 03:35:01PM +0000, Mathieu Desnoyers wrote:
> > > The page fault handler being very much performance sensitive, I'm
> > > wondering if it would not be better to move cow_page near the end of
> > > struct vm_fault, so that the "page" field can stay on the first
> > > cache line.
> 
> Although it's pretty much always true that recent architectures L2 cache
> lines are 64 bytes, I was more thinking about L1 cache lines, which are,
> at least on moderately old Intel Pentium HW, 32 bytes in size (AFAIK
> Pentium II and III).
> 
> It remains to be seen whether we care about performance that much on this
> kind of HW though.

Oh, I just remembered ... this data structure is on the stack, so if it's
not cache-hot, something has gone horribly wrong.

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