From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Fri, 4 Apr 2003 16:31:54 -0800 From: Andrew Morton Subject: Re: objrmap and vmtruncate Message-Id: <20030404163154.77f19d9e.akpm@digeo.com> In-Reply-To: <20030405000352.GF16293@dualathlon.random> References: <20030404105417.3a8c22cc.akpm@digeo.com> <20030404214547.GB16293@dualathlon.random> <20030404150744.7e213331.akpm@digeo.com> <20030405000352.GF16293@dualathlon.random> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Andrea Arcangeli Cc: mingo@elte.hu, hugh@veritas.com, dmccr@us.ibm.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: Andrea Arcangeli wrote: > > the worst part IMHO is that it screwup the vma making the vma->vm_file > totally wrong for the pages in the vma. Not sure what you mean here. All pages in the vma are backed by the file at vm_file. It is vm_pgoff which is meaningless. As for your other concerns: yes, I hear you. I suspect something will have to give. Ingo has a better feel for the problems which this code is solving and hopefully he can comment. Perhaps it is useful to itemise the prblems which we're trying to solve here: - ZONE_NORMAL consumption by pte_chains Solved by objrmap and presumably page clustering. - ZONE_NORMAL consumption by VMAs Solved by remap_file_pages. Neither objrmap nor page clustering will help here. - pte_chain setup and teardown CPU cost. objrmap does not seem to help. Page clustering might, but is unlikely to be enabled on the machines which actually care about the overhead. - get_unmapped_area() search complexity. Solved by remap_file_pages and by as-yet unimplemented algorithmic rework. - pagefault frequency and TLB invalidation cost. Solved by MAP_POPULATE, could also be solved by MAP_PREFAULT (but it's not really a demonstrated problem). Anything else? So looking at the above, remap_file_pages() actually has pretty good coverage. -- 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