From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Mon, 9 Oct 2006 14:14:17 +0200 From: Nick Piggin Subject: Re: [patch 3/3] mm: fault handler to replace nopage and populate Message-ID: <20061009121417.GA3785@wotan.suse.de> References: <20061009102635.GC3487@wotan.suse.de> <1160391014.10229.16.camel@localhost.localdomain> <20061009110007.GA3592@wotan.suse.de> <1160392214.10229.19.camel@localhost.localdomain> <20061009111906.GA26824@wotan.suse.de> <1160393579.10229.24.camel@localhost.localdomain> <20061009114527.GB26824@wotan.suse.de> <1160394571.10229.27.camel@localhost.localdomain> <20061009115836.GC26824@wotan.suse.de> <1160395671.10229.35.camel@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1160395671.10229.35.camel@localhost.localdomain> Sender: owner-linux-mm@kvack.org Return-Path: To: Benjamin Herrenschmidt Cc: Andrew Morton , Linux Memory Management , Linux Kernel List-ID: On Mon, Oct 09, 2006 at 10:07:50PM +1000, Benjamin Herrenschmidt wrote: > On Mon, 2006-10-09 at 13:58 +0200, Nick Piggin wrote: > > > > The VM won't see that you have struct pages backing the ptes, and won't > > do the right refcounting or rmap stuff... But for file backed mappings, > > all the critical rmap stuff should be set up at mmap time, so you might > > have another option to simply always do the nopfn thing, as far as the > > VM is concerned (ie. even when you do have a struct page) > > Any reason why it wouldn't work to flip that bit on the first no_page() > after a migration ? A migration always involves destroying all PTEs and > is done with a per-object mutex held that no_page() takes too, so we can > be pretty sure that the first nopage can set that bit before any PTE is > actually inserted in the mapping after all the previous ones have been > invalidated... That would avoid having to walk the vma's. Ok I guess that would work. I was kind of thinking that one needs to hold the mmap_sem for writing when changing the flags, but so long as everyone *else* does, then I guess you can get exclusion from just the read lock. And your per-object mutex would prevent concurrent nopages from modifying it. -- 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