From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: [PATCH 2.5.43-mm2] New shared page table patch References: <2577017645.1035188509@[10.10.2.3]> From: ebiederm@xmission.com (Eric W. Biederman) Date: 21 Oct 2002 21:54:21 -0600 In-Reply-To: <2577017645.1035188509@[10.10.2.3]> Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: owner-linux-mm@kvack.org Return-Path: To: "Martin J. Bligh" Cc: Bill Davidsen , Dave McCracken , Andrew Morton , Linux Kernel , Linux Memory Management List-ID: "Martin J. Bligh" writes: > >> In many cases, this will stop the box from falling over flat on it's > >> face due to ZONE_NORMAL exhaustion (from pte-chains), or even total > >> RAM exhaustion (from PTEs). Thus the performance gain is infinite ;-) > > > > So why has no one written a pte_chain reaper? It is perfectly sane > > to allocate a swap entry and move an entire pte_chain to the swap > > cache. > > I think the underlying subsystem does not easily allow for dynamic regeneration, > so it's non-trivial. We swap pages out all of the time in 2.4.x, and that is all I was suggesting swap out some but not all of the pages, on a very long pte_chain. And swapping out a page is not terribly complex, unless something very drastic has changed. > wli was looking at doing pagetable reclaim at some point, > IIRC. > > > IMHO, it's better not to fill memory with crap in the first place than > to invent complex methods of managing and shrinking it afterwards. You > only get into pathalogical conditions under sharing situation, else > it's limited to about 1% of RAM (bad, but manageable) ... thus providing > this sort of sharing nixes the worst of it. Better cache warmth on > switches (for TLB misses), faster fork+exec, etc. are nice side-effects. I will agree with that if everything works so the sharing happens, this is a nice feature. > The ultimate solution is per-object reverse mappings, rather than per > page, but that's a 2.7 thingy now. ??? Last I checked we already had those in 2.4.x, and still in 2.5.x. The list of place the address space is mapped. Eric -- 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/