Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756313Ab2FOQqK (ORCPT ); Fri, 15 Jun 2012 12:46:10 -0400 Received: from mail-pz0-f46.google.com ([209.85.210.46]:44837 "EHLO mail-pz0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752265Ab2FOQqI (ORCPT ); Fri, 15 Jun 2012 12:46:08 -0400 Message-ID: <4FDB66B7.2010803@vflare.org> Date: Fri, 15 Jun 2012 09:45:43 -0700 From: Nitin Gupta User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:13.0) Gecko/20120605 Thunderbird/13.0 MIME-Version: 1.0 To: Dan Magenheimer CC: Seth Jennings , Peter Zijlstra , Minchan Kim , Greg Kroah-Hartman , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Thomas Gleixner , Ingo Molnar , Tejun Heo , David Howells , x86@kernel.org, Nick Piggin , Konrad Rzeszutek Wilk Subject: Re: [PATCH v2 3/3] x86: Support local_flush_tlb_kernel_range References: <1337133919-4182-1-git-send-email-minchan@kernel.org> <1337133919-4182-3-git-send-email-minchan@kernel.org> <4FB4B29C.4010908@kernel.org> <1337266310.4281.30.camel@twins> <4FDB5107.3000308@linux.vnet.ibm.com> <7e925563-082b-468f-a7d8-829e819eeac0@default> In-Reply-To: <7e925563-082b-468f-a7d8-829e819eeac0@default> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3139 Lines: 80 On 06/15/2012 09:35 AM, Dan Magenheimer wrote: >> From: Seth Jennings [mailto:sjenning@linux.vnet.ibm.com] >> Sent: Friday, June 15, 2012 9:13 AM >> To: Peter Zijlstra >> Cc: Minchan Kim; Greg Kroah-Hartman; Nitin Gupta; Dan Magenheimer; linux-kernel@vger.kernel.org; >> linux-mm@kvack.org; Thomas Gleixner; Ingo Molnar; Tejun Heo; David Howells; x86@kernel.org; Nick >> Piggin >> Subject: Re: [PATCH v2 3/3] x86: Support local_flush_tlb_kernel_range >> >> On 05/17/2012 09:51 AM, Peter Zijlstra wrote: >> >>> On Thu, 2012-05-17 at 17:11 +0900, Minchan Kim wrote: >>>>> +++ b/arch/x86/include/asm/tlbflush.h >>>>> @@ -172,4 +172,16 @@ static inline void flush_tlb_kernel_range(unsigned long start, >>>>> flush_tlb_all(); >>>>> } >>>>> >>>>> +static inline void local_flush_tlb_kernel_range(unsigned long start, >>>>> + unsigned long end) >>>>> +{ >>>>> + if (cpu_has_invlpg) { >>>>> + while (start < end) { >>>>> + __flush_tlb_single(start); >>>>> + start += PAGE_SIZE; >>>>> + } >>>>> + } else >>>>> + local_flush_tlb(); >>>>> +} >>> >>> It would be much better if you wait for Alex Shi's patch to mature. >>> doing the invlpg thing for ranges is not an unconditional win. >> >> From what I can tell Alex's patches have stalled. The last post was v6 >> on 5/17 and there wasn't a single reply to them afaict. >> >> According to Alex's investigation of this "tipping point", it seems that >> a good generic value is 8. In other words, on most x86 hardware, it is >> cheaper to flush up to 8 tlb entries one by one rather than doing a >> complete flush. >> >> So we can do something like: >> >> if (cpu_has_invlpg && (end - start)/PAGE_SIZE <= 8) { >> while (start < end) { >> >> Would this be acceptable? > > Hey Seth, Nitin -- > > After more work digging around zsmalloc and zbud, I really think > this TLB flushing, as well as the "page pair mapping" code can be > completely eliminated IFF zsmalloc is limited to items PAGE_SIZE or > less. Since this is already true of zram (and in-tree zcache), and > zsmalloc currently has no other users, I think you should seriously > consider limiting zsmalloc in that way, or possibly splitting out > one version of zsmalloc which handles items PAGE_SIZE or less, > and a second version that can handle larger items but has (AFAIK) > no users. > > If you consider it an option to have (a version of) zsmalloc > limited to items PAGE_SIZE or less, let me know and we can > get into the details. > zsmalloc is already limited to objects of size PAGE_SIZE or less. This two-page splitting is for efficiently storing objects in range (PAGE_SIZE/2, PAGE_SIZE) which is very common in both zram and zcache. SLUB achieves this efficiency by allocating higher order pages but that is not an option for zsmalloc. Thanks, Nitin -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/