From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx140.postini.com [74.125.245.140]) by kanga.kvack.org (Postfix) with SMTP id A6A3D6B005A for ; Wed, 27 Jun 2012 11:13:36 -0400 (EDT) MIME-Version: 1.0 Message-ID: <90bcc2c8-bcac-4620-b3c0-6b65f8d9174d@default> Date: Wed, 27 Jun 2012 08:12:56 -0700 (PDT) From: Dan Magenheimer Subject: RE: [PATCH 3/3] x86: add local_tlb_flush_kernel_range() References: <1340640878-27536-1-git-send-email-sjenning@linux.vnet.ibm.com> <1340640878-27536-4-git-send-email-sjenning@linux.vnet.ibm.com> <4FEA9FDD.6030102@kernel.org> <4FEAA4AA.3000406@intel.com> <4FEAA7A1.9020307@kernel.org> In-Reply-To: <4FEAA7A1.9020307@kernel.org> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: Minchan Kim , Alex Shi Cc: Seth Jennings , Greg Kroah-Hartman , devel@driverdev.osuosl.org, Konrad Wilk , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Robert Jennings , Nitin Gupta > From: Minchan Kim [mailto:minchan@kernel.org] > Subject: Re: [PATCH 3/3] x86: add local_tlb_flush_kernel_range() >=20 > Hello, >=20 > On 06/27/2012 03:14 PM, Alex Shi wrote: >=20 > > On 06/27/2012 01:53 PM, Minchan Kim wrote: > > > >> On 06/26/2012 01:14 AM, Seth Jennings wrote: > >> > >>> This patch adds support for a local_tlb_flush_kernel_range() > >>> function for the x86 arch. This function allows for CPU-local > >>> TLB flushing, potentially using invlpg for single entry flushing, > >>> using an arch independent function name. > >>> > >>> Signed-off-by: Seth Jennings > >> > >> > >> Anyway, we don't matter INVLPG_BREAK_EVEN_PAGES's optimization point i= s 8 or something. > > > > > > Different CPU type has different balance point on the invlpg replacing > > flush all. and some CPU never get benefit from invlpg, So, it's better > > to use different value for different CPU, not a fixed > > INVLPG_BREAK_EVEN_PAGES. >=20 > I think it could be another patch as further step and someone who are > very familiar with architecture could do better than. > So I hope it could be merged if it doesn't have real big problem. >=20 > Thanks for the comment, Alex. Just my opinion, but I have to agree with Alex. Hardcoding behavior that is VERY processor-specific is a bad idea. TLBs should only be messed with when absolutely necessary, not for the convenience of defending an abstraction that is nice-to-have but, in current OS kernel code, unnecessary. IIUC, zsmalloc only cares that the breakeven point is greater than two. An arch-specific choice of (A) two page flushes vs (B) one all-TLB flush should be all that is necessary right now. (And, per separate discussion, even this isn't really necessary either.) If zsmalloc _ever_ gets extended to support items that might span three or more pages, a more generic TLB flush-pages-vs-flush-all approach may be warranted and, by then, may already exist in some future kernel. Until then, IMHO, keep it simple. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org