From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <48A9F047.7050906@cisco.com> Date: Mon, 18 Aug 2008 14:57:27 -0700 From: David VomLehn MIME-Version: 1.0 Subject: Re: sparsemem support for mips with highmem References: <48A4AC39.7020707@sciatl.com> <1218753308.23641.56.camel@nimitz> <48A4C542.5000308@sciatl.com> <20080815080331.GA6689@alpha.franken.de> <1218815299.23641.80.camel@nimitz> <48A5AADE.1050808@sciatl.com> <20080815163302.GA9846@alpha.franken.de> <48A5B9F1.3080201@sciatl.com> <1218821875.23641.103.camel@nimitz> <48A5C831.3070002@sciatl.com> <20080818094412.09086445.rdunlap@xenotime.net> <48A9E89C.4020408@linux-foundation.org> In-Reply-To: <48A9E89C.4020408@linux-foundation.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Christoph Lameter Cc: Randy Dunlap , C Michael Sundius , Dave Hansen , Thomas Bogendoerfer , linux-mm@kvack.org, linux-mips@linux-mips.org, jfraser@broadcom.com, Andy Whitcroft List-ID: Christoph Lameter wrote: > Randy Dunlap wrote: > >> +Sparsemem divides up physical memory in your system into N section of M >> >> sections >> >> +bytes. Page descriptors are created for only those sections that >> +actually exist (as far as the sparsemem code is concerned). This allows >> +for holes in the physical memory without having to waste space by >> +creating page discriptors for those pages that do not exist. >> >> descriptors >> >> +When page_to_pfn() or pfn_to_page() are called there is a bit of overhead to >> +look up the proper memory section to get to the descriptors, but this >> +is small compared to the memory you are likely to save. So, it's not the >> +default, but should be used if you have big holes in physical memory. > > This overhead can be avoided by configuring sparsemem to use a virtual vmemmap > (CONFIG_SPARSEMEM_VMEMMAP). In that case it can be used for non NUMA since the > overhead is less than even FLATMEM. On MIPS processors, the kernel runs in unmapped memory, i.e. the TLB isn't even used, so I don't think you can use that trick. So, this comment doesn't apply to all processors. -- 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