From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f197.google.com (mail-wr0-f197.google.com [209.85.128.197]) by kanga.kvack.org (Postfix) with ESMTP id 1C8E06B0279 for ; Tue, 20 Jun 2017 17:08:35 -0400 (EDT) Received: by mail-wr0-f197.google.com with SMTP id 77so11256751wrb.11 for ; Tue, 20 Jun 2017 14:08:35 -0700 (PDT) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTPS id 7si15600359wrc.13.2017.06.20.14.08.33 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 20 Jun 2017 14:08:33 -0700 (PDT) Date: Tue, 20 Jun 2017 14:08:31 -0700 From: Andrew Morton Subject: Re: [PATCH v5 0/8] Support for contiguous pte hugepages Message-Id: <20170620140831.6bd835649d475bcf30c3c434@linux-foundation.org> In-Reply-To: <871sqezsk2.fsf@e105922-lin.cambridge.arm.com> References: <20170619170145.25577-1-punit.agrawal@arm.com> <20170619150133.cb4173220e4e3abd02c6f6d0@linux-foundation.org> <871sqezsk2.fsf@e105922-lin.cambridge.arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Punit Agrawal Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, catalin.marinas@arm.com, will.deacon@arm.com, n-horiguchi@ah.jp.nec.com, kirill.shutemov@linux.intel.com, mike.kravetz@oracle.com, steve.capper@arm.com, mark.rutland@arm.com, linux-arch@vger.kernel.org, aneesh.kumar@linux.vnet.ibm.com On Tue, 20 Jun 2017 14:39:57 +0100 Punit Agrawal wrote: > > The architecture supports two flavours of hugepages - > > * Block mappings at the pud/pmd level > > These are regular hugepages where a pmd or a pud page table entry > points to a block of memory. Depending on the PAGE_SIZE in use the > following size of block mappings are supported - > > PMD PUD > --- --- > 4K: 2M 1G > 16K: 32M > 64K: 512M > > For certain applications/usecases such as HPC and large enterprise > workloads, folks are using 64k page size but the minimum hugepage size > of 512MB isn't very practical. > > To overcome this ... > > * Using the Contiguous bit > > The architecture provides a contiguous bit in the translation table > entry which acts as a hint to the mmu to indicate that it is one of a > contiguous set of entries that can be cached in a single TLB entry. > > We use the contiguous bit in Linux to increase the mapping size at the > pmd and pte (last) level. > > The number of supported contiguous entries varies by page size and > level of the page table. > > Using the contiguous bit allows additional hugepage sizes - > > CONT PTE PMD CONT PMD PUD > -------- --- -------- --- > 4K: 64K 2M 32M 1G > 16K: 2M 32M 1G > 64K: 2M 512M 16G > > Of these, 64K with 4K and 2M with 64K pages have been explicitly > requested by a few different users. > > Entries with the contiguous bit set are required to be modified all > together - which makes things like memory poisoning and migration > impossible to do correctly without knowing the size of hugepage being > dealt with - the reason for adding size parameter to a few of the > hugepage helpers in this series. > Thanks, I added the above to the 1/n changelog. Perhaps it's worth adding something like this to Documentation/vm/hugetlbpage.txt. -- 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