From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 3 Jul 2003 11:53:41 -0700 From: William Lee Irwin III Subject: Re: What to expect with the 2.6 VM Message-ID: <20030703185341.GJ20413@holomorphy.com> References: <20030703125839.GZ23578@dualathlon.random> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org Return-Path: To: Rik van Riel Cc: Andrea Arcangeli , "Martin J. Bligh" , Mel Gorman , Linux Memory Management List , Linux Kernel Mailing List List-ID: On Thu, 3 Jul 2003, Andrea Arcangeli wrote: >> even if you don't use largepages as you should, the ram cost of the pte >> is nothing on 64bit archs, all you care about is to use all the mhz and >> tlb entries of the cpu. On Thu, Jul 03, 2003 at 09:06:32AM -0400, Rik van Riel wrote: > That depends on the number of Oracle processes you have. > Say that page tables need 0.1% of the space of the virtual > space they map. With 1000 Oracle users you'd end up needing > as much memory in page tables as your shm segment is large. > Of course, in this situation either the application should > use large pages or the kernel should simply reclaim the > page tables (possible while holding the mmap_sem for write). No, it is not true that pagetable space can be wantonly wasted on 64-bit. Try mmap()'ing something sufficiently huge and accessing on average every PAGE_SIZE'th virtual page, in a single-threaded single process. e.g. various indexing schemes might do this. This is 1 pagetable page per page of data (worse if shared), which blows major goats. There's a reason why those things use inverted pagetables... at any rate, compacting virtualspace with remap_file_pages() solves it too. Large pages won't help, since the data isn't contiguous. -- wli -- 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: aart@kvack.org