From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from chimera.site ([72.90.117.230]) by xenotime.net for ; Mon, 18 Aug 2008 09:43:37 -0700 Date: Mon, 18 Aug 2008 09:44:12 -0700 From: Randy Dunlap Subject: Re: sparsemem support for mips with highmem Message-Id: <20080818094412.09086445.rdunlap@xenotime.net> In-Reply-To: <48A5C831.3070002@sciatl.com> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: C Michael Sundius Cc: Dave Hansen , Thomas Bogendoerfer , linux-mm@kvack.org, linux-mips@linux-mips.org, jfraser@broadcom.com, Andy Whitcroft List-ID: On Fri, 15 Aug 2008 11:17:21 -0700 C Michael Sundius wrote: > Ah, compromise :] that's why you get paid the big bux dave. thanks. Here are some documentation comments/corrections. And please try to use inline patches instead of attachments. See Documenation/email-clients.txt for some help on this. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ diff --git a/Documentation/sparsemem.txt b/Documentation/sparsemem.txt new file mode 100644 index 0000000..89656e3 --- /dev/null +++ b/Documentation/sparsemem.txt @@ -0,0 +1,96 @@ +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. + +Note that discontiguous memory is more closely related to NUMA machines +and if you are a single CPU system use sparsemem and not discontig. +It's much simpler. + +1) CALL MEMORY_PRESENT() +Once the bootmem allocator is up and running, you should call the +sparsemem function "memory_present(node, pfn_start, pfn_end)" for each +block of memory that exists on your system. + +2) DETERMINE AND SET THE SIZE OF SECTIONS AND PHYSMEM ... +3) INITIALIZE SPARSE MEMORY +You should make sure that you initialize the sparse memory code by calling + + bootmem_init(); + + sparse_init(); + paging_init(); + +just before you call paging_init() and after the bootmem_allocator is +turned on in your setup_arch() code. + +4) ENABLE SPARSEMEM IN KCONFIG +Add a line like this: + + select ARCH_SPARSEMEM_ENABLE + +into the config for your platform in arch//Kconfig. This will +ensure that turning on sparsemem is enabled for your platform. + +5) CONFIG +Run make menuconfig or make gconfig, as you like, and turn on the sparsemem +memory model under the "Kernel Type" --> "Memory Model" and then build your +kernel. Wow! A gconfig user? I see more people using menuconfig or xconfig IIRC. Anyway, we usually just say something like "run make *config"... + + +6) Gotchas + +One trick that I encountered when I was turning this on for MIPS was that there +was some code in mem_init() that set the "reserved" flag for pages that were not +valid RAM. This caused my kernel to crash when I enabled sparsemem since those +pages (and page descriptors) didn't actually exist. I changed my code by adding +lines like below: + + + for (tmp = highstart_pfn; tmp < highend_pfn; tmp++) { + struct page *page = pfn_to_page(tmp); + + + if (!pfn_valid(tmp)) + + continue; + + + if (!page_is_ram(tmp)) { + SetPageReserved(page); + continue; + } + ClearPageReserved(page); + init_page_count(page); + __free_page(page); + physmem_record(PFN_PHYS(tmp), PAGE_SIZE, physmem_highmem); + totalhigh_pages++; + } + + +Once I got that straight, it worked!!!! I saved 10MiB of memory. Please don't end patch lines with whitespace. (like above) --- ~Randy Linux Plumbers Conference, 17-19 September 2008, Portland, Oregon USA http://linuxplumbersconf.org/ -- 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