From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with SMTP id 1AE636B010E for ; Wed, 22 Jul 2009 08:54:15 -0400 (EDT) Date: Wed, 22 Jul 2009 13:54:06 +0100 (BST) From: Hugh Dickins Subject: Re: [PATCH 06/10] ksm: identify PageKsm pages In-Reply-To: <4A660101.3000307@redhat.com> Message-ID: References: <1247851850-4298-1-git-send-email-ieidus@redhat.com> <1247851850-4298-2-git-send-email-ieidus@redhat.com> <1247851850-4298-3-git-send-email-ieidus@redhat.com> <1247851850-4298-4-git-send-email-ieidus@redhat.com> <1247851850-4298-5-git-send-email-ieidus@redhat.com> <1247851850-4298-6-git-send-email-ieidus@redhat.com> <1247851850-4298-7-git-send-email-ieidus@redhat.com> <20090721175139.GE2239@random.random> <4A660101.3000307@redhat.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org To: Rik van Riel Cc: Andrea Arcangeli , Izik Eidus , akpm@linux-foundation.org, chrisw@redhat.com, avi@redhat.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, nickpiggin@yahoo.com.au, Wu Fengguang List-ID: On Tue, 21 Jul 2009, Rik van Riel wrote: > Andrea Arcangeli wrote: > > > - if (PageAnon(old_page)) { > > > + if (PageAnon(old_page) && !PageKsm(old_page)) { > > > if (!trylock_page(old_page)) { > > > page_cache_get(old_page); > > > pte_unmap_unlock(page_table, ptl); > > > > What exactly does it buy to have PageAnon return 1 on ksm pages, > > besides requiring the above additional check (that if we stick to the > > above code, I would find safer to move inside reuse_swap_page). > > I guess that if they are to remain unswappable, they > should go onto the unevictable list. The KSM pages are not put on any LRU, so wouldn't be slowing vmscan down with futile scans: isn't the unevictable list for pages which belong to another LRU once they become evictable again? (At this instant I've forgotten why there's an unevictable list at all - somewhere in vmscan.c which is accustomed to dealing with pages on lists, so easier to have them on a list than not?) > > Then again, I'm guessing this is all about to change > in not too much time :) Yes, I'd much rather put the effort into making them swappable, than fiddling with counts here and there to highlight their current unswappability. Hugh -- 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