From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: [RFC][patch 0/2] mm: remove PageReserved From: Benjamin Herrenschmidt In-Reply-To: References: <42F57FCA.9040805@yahoo.com.au> <200508090710.00637.phillips@arcor.de> <42F7F5AE.6070403@yahoo.com.au> <1123577509.30257.173.camel@gaston> <1123597903.30257.204.camel@gaston> Content-Type: text/plain Date: Tue, 09 Aug 2005 16:49:11 +0200 Message-Id: <1123598952.30257.213.camel@gaston> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Hugh Dickins Cc: Nick Piggin , Daniel Phillips , linux-kernel , Linux Memory Management , Linus Torvalds , Andrew Morton , Andrea Arcangeli List-ID: On Tue, 2005-08-09 at 15:50 +0100, Hugh Dickins wrote: > On Tue, 9 Aug 2005, Benjamin Herrenschmidt wrote: > > > > > But you don't mind if they are refcounted, do you? > > > Just so long as they start out from 1 so never get freed. > > > > Well, a refcounting bug would let them be freed and kaboom ... That's > > why a "PG_not_your_ram_dammit" bit would be useful. It could at least > > BUG_ON when refcount reaches 0 :) > > Okay, great, let's give every struct page two refcounts, > so if one of them goes wrong, the other one will save us. You are abusing here :) - We already have a refcount - We have a field where putting a flag isn't that much of a problem - It can be difficult to get page refcounting right when dealing with such things, really. In that case, we basically have an _easy_ way to trigger a useful BUG() in the page free path when it's a page that should never be returned to the pool. Since the "PG_not_in_ram" or whatever we call it flag might be used by swsusp or others, I suppose it could be useful. However, I agree that if the end result is to have drivers just change "PG_reserved" to "PG_not_in_ram" and still be bogus, then we might just go all the way & drop the flag completely, only relying on the VMA flags. Ben. -- 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