From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Sun, 21 Aug 2005 21:06:25 -0700 (PDT) From: Christoph Lameter Subject: Re: [PATCH] Use deltas to replace atomic inc In-Reply-To: Message-ID: References: <20050817151723.48c948c7.akpm@osdl.org> <20050817174359.0efc7a6a.akpm@osdl.org> <20050818212939.7dca44c3.akpm@osdl.org> <20050820005843.21ba4d9b.akpm@osdl.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org Return-Path: To: Linus Torvalds Cc: Andrew Morton , hugh@veritas.com, nickpiggin@yahoo.com.au, linux-mm@kvack.org List-ID: On Sun, 21 Aug 2005, Linus Torvalds wrote: > On Sun, 21 Aug 2005, Christoph Lameter wrote: > > > > The thing that bothers me more is that schedule() can be called both by > > handle_mm_fault as well as during unuse_mm. We may need some flag > > PF_NO_COUNTER_UPDATES or so there to insure that schedule() does not add > > deltas to the current->mm. > > Why? I don't think it's ever wrong to do the thing. We should be holding > no locks at the point (and we haven't grabbed he RQ lock yet), so it > should always be safe to get the page table lock. get_user_pages and unuse_mm may be working on an mm that is not current->mm. If schedule is called then the deltas are added to the wrong mm (current->mm). If we had PF_NO_COUNTER_UPDATES then we could force no counters updates to occur until get_user_pages or unuse_mm assigns the deltas to a specific mm using mm_counter_catchup(current, target_mm). > I think the delta approach looks quite reasonable, although I think > somebody should check that the cache behaviour is ok (ie the deltas should > hopefully be in a cacheline that we need to look at anyway). I put the deltas near to exit_state which is also checked in schedule(). -- 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