From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-x235.google.com (mail-pa0-x235.google.com [IPv6:2607:f8b0:400e:c03::235]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id BE03C1A060D for ; Fri, 19 Feb 2016 15:31:27 +1100 (AEDT) Received: by mail-pa0-x235.google.com with SMTP id fl4so43357541pad.0 for ; Thu, 18 Feb 2016 20:31:27 -0800 (PST) Subject: Re: [PATCH] powerpc/Kconfig: Update config option based on page size. To: Balbir Singh References: <1455846943-32147-1-git-send-email-rashmicy@gmail.com> <56C69535.90907@gmail.com> From: Rashmica Cc: Michael Ellerman , linuxppc-dev@lists.ozlabs.org Message-ID: <56C69A98.3020800@gmail.com> Date: Fri, 19 Feb 2016 15:31:20 +1100 MIME-Version: 1.0 In-Reply-To: <56C69535.90907@gmail.com> Content-Type: text/plain; charset=utf-8; format=flowed List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On 19/02/16 15:08, Balbir Singh wrote: > > On 19/02/16 12:55, Rashmica Gupta wrote: >> Currently on PPC64 changing kernel pagesize from 4K to 64K leaves >> FORCE_MAX_ZONEORDER set to 13 - which produces a compile error. >> >> The error occurs because of the following constraint (from >> include/linux/mmzone.h) being violated: >> >> MAX_ORDER -1 + PAGESHIFT <= SECTION_SIZE_BITS. > IA64 has this cool hack > > 12 #ifdef CONFIG_FORCE_MAX_ZONEORDER > 13 #if ((CONFIG_FORCE_MAX_ZONEORDER - 1 + PAGE_SHIFT) > SECTION_SIZE_BITS) > 14 #undef SECTION_SIZE_BITS > 15 #define SECTION_SIZE_BITS (CONFIG_FORCE_MAX_ZONEORDER - 1 + PAGE_SHIFT) > 16 #endif > > But coming back (we can revisit the SECTION_SIZE_BITS definition later) I feel like someone more senior than me should weigh in on if this is worth doing... > MAX_ORDER -1 + 16 <= 24 for 64 K > > and > > MAX_ORDER -1 + 12 < = 24 for 4K > > Your calculations are correct >> Expanding this out, we get: >> >> FORCE_MAX_ZONEBITS <= 25 - PAGESHIFT, >> >> which requires, for a 64K page, FORCE_MAX_ZONEBITS <= 9. Thus >> set max value of FORCE_MAX_ZONEORDER for 64K pages to 9. >> >> Also, check the minimum value: >> In include/linux/huge_mm.h, we have the constraint HPAGE_PMD_ORDER < >> MAX_ORDER which expands out to: >> >> PTE_INDEX_SIZE < FORCE_MAX_ZONEORDER. >> PTE_INDEX_SIZE is: >> 9 (4k hash or no hash 4K pgtable) or >> 8 (64K hash or no hash 64K pgtable). >> Thus a min value of 9 for 64K pages is reasonable. > For 4K pages we end up with > > 9 < FORCE_MAX_ZONE_ORDER > FORCE_MAX_ZONE_ORDER -1 + 12 < = 24 > > The range is 9 to 13 > > For 64K we end up with > 8 < FORCE_MAX_ZONE_ORDER > FORCE_MAX_ZONE_ORDER -1 + 16 <= 24 or FORCE_MAX_ZONE_ORDER <= 9 > > The range is really between 8 and 9 unless we tweak the SECTION_SIZE_BITS Yup, you are right! Might have had a brain spaz... >> So, update the range of FORCE_MAX_ZONEORDER from 9-64 to 9-9. >> >> Signed-off-by: Rashmica Gupta >> --- >> arch/powerpc/Kconfig | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig >> index e4824fd04bb7..3bd3465b93ba 100644 >> --- a/arch/powerpc/Kconfig >> +++ b/arch/powerpc/Kconfig >> @@ -585,7 +585,7 @@ endchoice >> >> config FORCE_MAX_ZONEORDER >> int "Maximum zone order" >> - range 9 64 if PPC64 && PPC_64K_PAGES >> + range 9 9 if PPC64 && PPC_64K_PAGES > range 8 9? Agreed. >> default "9" if PPC64 && PPC_64K_PAGES >> range 13 64 if PPC64 && !PPC_64K_PAGES > Should this be fixed as well? > range 9 13? Agreed. >> default "13" if PPC64 && !PPC_64K_PAGES Should the default values remain as is, or follow the trend and be equal to the minimum value? > Please check my calculations > > Reviewed-by: Balbir Singh > > Balbir Singh