From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with SMTP id 826E9600309 for ; Mon, 30 Nov 2009 07:38:35 -0500 (EST) Date: Mon, 30 Nov 2009 12:38:33 +0000 (GMT) From: Hugh Dickins Subject: Re: [PATCH 2/9] ksm: let shared pages be swappable In-Reply-To: <20091130180452.5BF6.A69D9226@jp.fujitsu.com> Message-ID: References: <20091130094616.8f3d94a7.kamezawa.hiroyu@jp.fujitsu.com> <20091130180452.5BF6.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org To: KOSAKI Motohiro Cc: KAMEZAWA Hiroyuki , Andrew Morton , Izik Eidus , Andrea Arcangeli , Chris Wright , linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: On Mon, 30 Nov 2009, KOSAKI Motohiro wrote: > > After this patch, the number of shared swappable page will be unlimited. > > Probably, it doesn't matter. I mean > > - KSM sharing and Shmem sharing are almost same performance characteristics. > - if memroy pressure is low, SplitLRU VM doesn't scan anon list so much. > > if ksm swap is too costly, we need to improve anon list scanning generically. Yes, we're in agreement that this issue is not new with KSM swapping. > btw, I'm not sure why bellow kmem_cache_zalloc() is necessary. Why can't we > use stack? Well, I didn't use stack: partly because I'm so ashamed of the pseudo-vmas on the stack in mm/shmem.c, which have put shmem_getpage() into reports of high stack users (I've unfinished patches to deal with that); and partly because page_referenced_ksm() and try_to_unmap_ksm() are on the page reclaim path, maybe way down deep on a very deep stack. But it's not something you or I should be worrying about: as the comment says, this is just a temporary hack, to present a patch which gets KSM swapping working in an understandable way, while leaving some corrections and refinements to subsequent patches. This pseudo-vma is removed in the very next patch. Hugh > > ---------------------------- > + /* > + * Temporary hack: really we need anon_vma in rmap_item, to > + * provide the correct vma, and to find recently forked instances. > + * Use zalloc to avoid weirdness if any other fields are involved. > + */ > + vma = kmem_cache_zalloc(vm_area_cachep, GFP_ATOMIC); > + if (!vma) { > + spin_lock(&ksm_fallback_vma_lock); > + vma = &ksm_fallback_vma; > + } -- 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