linux-kernel - Re: [PATCH 2/3] zsmalloc: add generic path and remove x86 dependency

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Message-ID: <20120625233737.GA3493@kroah.com>
Date:	Mon, 25 Jun 2012 16:37:37 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Seth Jennings <sjenning@...ux.vnet.ibm.com>
Cc:	devel@...verdev.osuosl.org,
	Dan Magenheimer <dan.magenheimer@...cle.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Minchan Kim <minchan@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Robert Jennings <rcj@...ux.vnet.ibm.com>,
	Nitin Gupta <ngupta@...are.org>
Subject: Re: [PATCH 2/3] zsmalloc: add generic path and remove x86 dependency

On Mon, Jun 25, 2012 at 01:24:29PM -0500, Seth Jennings wrote:
> On 06/25/2012 12:19 PM, Greg Kroah-Hartman wrote:
> > On Mon, Jun 25, 2012 at 12:10:57PM -0500, Seth Jennings wrote:
> >> On 06/25/2012 11:59 AM, Greg Kroah-Hartman wrote:
> >>> On Mon, Jun 25, 2012 at 11:14:37AM -0500, Seth Jennings wrote:
> >>>> This patch adds generic pages mapping methods that
> >>>> work on all archs in the absence of support for
> >>>> local_tlb_flush_kernel_range() advertised by the
> >>>> arch through __HAVE_LOCAL_TLB_FLUSH_KERNEL_RANGE
> >>>
> >>> Is this #define something that other arches define now?  Or is this
> >>> something new that you are adding here?
> >>
> >> Something new I'm adding.
> > 
> > Ah, ok.
> > 
> >> The precedent for this approach is the __HAVE_ARCH_* defines
> >> that let the arch independent stuff know if a generic
> >> function needs to be defined or if there is an arch specific
> >> function.
> >>
> >> You can "grep -R __HAVE_ARCH_* arch/x86/" to see the ones
> >> that already exist.
> >>
> >> I guess I should have called it
> >> __HAVE_ARCH_LOCAL_TLB_FLUSH_KERNEL_RANGE though, not
> >> __HAVE_LOCAL_TLB_FLUSH_KERNEL_RANGE.
> > 
> > You need to get the mm developers to agree with this before I can take
> > it.
> > 
> > But, why even depend on this?  Can't you either live without it
> 
> The whole point of the patch is _not_ to depend on it.  It
> just performs worse without it.  We could just rip out all
> the the page table assisted page mapping, but, for the
> arches that have support for it, we'd be degrading
> performance in exchange for portability.  Why choose when we
> can have both?

Ok, I'll let you fight it out with the mm people before applying these 2
patches, I've applied the first one only for now.

greg k-h
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