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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Thu, 28 Feb 2019 12:43:34 -0000 Received: from b01ledav003.gho.pok.ibm.com (b01ledav003.gho.pok.ibm.com [9.57.199.108]) by b01cxnp22034.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x1SChX8u20381722 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 28 Feb 2019 12:43:33 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 4E510B2066; Thu, 28 Feb 2019 12:43:33 +0000 (GMT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 0E7B5B205F; Thu, 28 Feb 2019 12:43:30 +0000 (GMT) Received: from [9.199.36.171] (unknown [9.199.36.171]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Thu, 28 Feb 2019 12:43:29 +0000 (GMT) Subject: Re: [PATCH 2/2] mm/dax: Don't enable huge dax mapping by default To: Oliver , Dan Williams Cc: Andrew Morton , "Kirill A . Shutemov" , Jan Kara , Michael Ellerman , Ross Zwisler , Linux MM , Linux Kernel Mailing List , linuxppc-dev References: <20190228083522.8189-1-aneesh.kumar@linux.ibm.com> <20190228083522.8189-2-aneesh.kumar@linux.ibm.com> From: "Aneesh Kumar K.V" Date: Thu, 28 Feb 2019 18:13:28 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 x-cbid: 19022812-0068-0000-0000-0000039BAD11 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00010679; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000281; SDB=6.01167576; UDB=6.00609980; IPR=6.00948189; MB=3.00025780; MTD=3.00000008; XFM=3.00000015; UTC=2019-02-28 12:43:37 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19022812-0069-0000-0000-000047A84445 Message-Id: <65e1671d-6896-e2e9-e000-90c5b0484ad2@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-02-28_06:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1902280088 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2/28/19 3:10 PM, Oliver wrote: > On Thu, Feb 28, 2019 at 7:35 PM Aneesh Kumar K.V > wrote: >> >> Add a flag to indicate the ability to do huge page dax mapping. On architecture >> like ppc64, the hypervisor can disable huge page support in the guest. In >> such a case, we should not enable huge page dax mapping. This patch adds >> a flag which the architecture code will update to indicate huge page >> dax mapping support. > > *groan* > >> Architectures mostly do transparent_hugepage_flag = 0; if they can't >> do hugepages. That also takes care of disabling dax hugepage mapping >> with this change. >> >> Without this patch we get the below error with kvm on ppc64. >> >> [ 118.849975] lpar: Failed hash pte insert with error -4 >> >> NOTE: The patch also use >> >> echo never > /sys/kernel/mm/transparent_hugepage/enabled >> to disable dax huge page mapping. >> >> Signed-off-by: Aneesh Kumar K.V >> --- >> TODO: >> * Add Fixes: tag >> >> include/linux/huge_mm.h | 4 +++- >> mm/huge_memory.c | 4 ++++ >> 2 files changed, 7 insertions(+), 1 deletion(-) >> >> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h >> index 381e872bfde0..01ad5258545e 100644 >> --- a/include/linux/huge_mm.h >> +++ b/include/linux/huge_mm.h >> @@ -53,6 +53,7 @@ vm_fault_t vmf_insert_pfn_pud(struct vm_area_struct *vma, unsigned long addr, >> pud_t *pud, pfn_t pfn, bool write); >> enum transparent_hugepage_flag { >> TRANSPARENT_HUGEPAGE_FLAG, >> + TRANSPARENT_HUGEPAGE_DAX_FLAG, >> TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, >> TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, >> TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, >> @@ -111,7 +112,8 @@ static inline bool __transparent_hugepage_enabled(struct vm_area_struct *vma) >> if (transparent_hugepage_flags & (1 << TRANSPARENT_HUGEPAGE_FLAG)) >> return true; >> >> - if (vma_is_dax(vma)) >> + if (vma_is_dax(vma) && >> + (transparent_hugepage_flags & (1 << TRANSPARENT_HUGEPAGE_DAX_FLAG))) >> return true; > > Forcing PTE sized faults should be fine for fsdax, but it'll break > devdax. The devdax driver requires the fault size be >= the namespace > alignment since devdax tries to guarantee hugepage mappings will be > used and PMD alignment is the default. We can probably have devdax > fall back to the largest size the hypervisor has made available, but > it does run contrary to the design. Ah well, I suppose it's better off > being degraded rather than unusable. > Will fix that. I will make PFN_DEFAULT_ALIGNMENT arch specific. >> if (transparent_hugepage_flags & >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >> index faf357eaf0ce..43d742fe0341 100644 >> --- a/mm/huge_memory.c >> +++ b/mm/huge_memory.c >> @@ -53,6 +53,7 @@ unsigned long transparent_hugepage_flags __read_mostly = >> #ifdef CONFIG_TRANSPARENT_HUGEPAGE_MADVISE >> (1<> #endif >> + (1 << TRANSPARENT_HUGEPAGE_DAX_FLAG) | >> (1<> (1<> (1<> @@ -475,6 +476,8 @@ static int __init setup_transparent_hugepage(char *str) >> &transparent_hugepage_flags); >> clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, >> &transparent_hugepage_flags); >> + clear_bit(TRANSPARENT_HUGEPAGE_DAX_FLAG, >> + &transparent_hugepage_flags); >> ret = 1; >> } >> out: > >> @@ -753,6 +756,7 @@ static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr, >> spinlock_t *ptl; >> >> ptl = pmd_lock(mm, pmd); >> + /* should we check for none here again? */ > > VM_WARN_ON() maybe? If THP is disabled and we're here then something > has gone wrong. I was wondering whether we can end up calling insert_pfn_pmd in parallel and hence end up having a pmd entry here already. Usually we check for if (!pmd_none(pmd)) after holding pmd_lock. Was not sure whether there is anything preventing a parallel fault in case of dax. > >> entry = pmd_mkhuge(pfn_t_pmd(pfn, prot)); >> if (pfn_t_devmap(pfn)) >> entry = pmd_mkdevmap(entry); >> -- >> 2.20.1 >> >