From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <41C41ACE.7060002@yahoo.com.au> Date: Sat, 18 Dec 2004 22:55:58 +1100 From: Nick Piggin MIME-Version: 1.0 Subject: Re: [PATCH 4/10] alternate 4-level page tables patches References: <41C3D453.4040208@yahoo.com.au> <41C3D479.40708@yahoo.com.au> <41C3D48F.8080006@yahoo.com.au> <41C3D4AE.7010502@yahoo.com.au> <41C3D4C8.1000508@yahoo.com.au> <41C3F2D6.6060107@yahoo.com.au> <20041218095050.GC338@wotan.suse.de> <41C40125.3060405@yahoo.com.au> <20041218110608.GJ771@holomorphy.com> <41C411BD.6090901@yahoo.com.au> <20041218113252.GK771@holomorphy.com> In-Reply-To: <20041218113252.GK771@holomorphy.com> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: William Lee Irwin III Cc: Andi Kleen , Linux Memory Management , Hugh Dickins , Linus Torvalds , Andrew Morton List-ID: William Lee Irwin III wrote: > William Lee Irwin III wrote: > >>>If this were so, then clear_page_tables() during process destruction >>>would be unnecessary. detach_vmas_to_be_unmapped() makes additional >>>work for such schemes, but even improvements are still rather helpful. > > > On Sat, Dec 18, 2004 at 10:17:17PM +1100, Nick Piggin wrote: > >>If what were so? > > > If clear_page_tables() implemented perfect GC. > Oh... well it does perfectly free memory in the context of what ranges have been previously cleared with clear_page_tables. So that doesn't free you from the requirement of calling clear_page_tables at some point. I suspect though, you are referring to refcounting, in which case yes, GC could probably be performed at unmap time, and clear_page_tables could disappear. I still think it would be too costly to refcount down to the pte_t level, especially SMP-wise.... but I'm just basing that on a few minutes of thought, so - I don't really know. > > On Sat, Dec 18, 2004 at 09:06:29PM +1100, Nick Piggin wrote: > >>>>Although I think it would enable you to do page table reclaim when >>>>reclaiming mapped, file backed pages quite easily... but I'm not sure if >>>>that is enough to offset the slowdowns. > > > William Lee Irwin III wrote: > >>>That would be a far more appropriate response to high multiprogramming >>>levels than what is now done. > > > On Sat, Dec 18, 2004 at 10:17:17PM +1100, Nick Piggin wrote: > >>On a select few workloads, yes. > > > Counterexamples would be illustrative. > Oh, just workloads where memory is fairly dense in virtual space, and not shared (much). Non-oracle workloads, perhaps? :) Seriously? On my typical desktop, I have 250MB used, of which 1MB is page tables, I suspect this is a pretty typical ratio on desktops, but I have less experience with high end database servers and that type of stuff. I was hoping you could provide an example rather than me a counter ;) -- 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