From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Mon, 27 Jun 2005 18:22:54 -0700 From: William Lee Irwin III Subject: Re: [patch 2] mm: speculative get_page Message-ID: <20050628012254.GO3334@holomorphy.com> References: <42BF9CD1.2030102@yahoo.com.au> <42BF9D67.10509@yahoo.com.au> <42BF9D86.90204@yahoo.com.au> <20050627141220.GM3334@holomorphy.com> <42C093B4.3010707@yahoo.com.au> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <42C093B4.3010707@yahoo.com.au> Sender: owner-linux-mm@kvack.org Return-Path: To: Nick Piggin Cc: linux-kernel , Linux Memory Management List-ID: William Lee Irwin III wrote: >> SetPageFreeing is only done in shrink_list(), so other pages in the >> buddy bitmaps and/or pagecache pages freed by other methods may not On Tue, Jun 28, 2005 at 10:03:00AM +1000, Nick Piggin wrote: > It is also done by remove_exclusive_swap_page, although that hunk > leaked into a later patch (#5), sorry. > Other methods (eg truncate) don't seem to have an atomicity guarantee > anyway - ie. it is valid to pick up a reference on a page that is > just about to get truncated. PageFreeing is only used when some code > is making an assumption about the number of users of the page. tmpfs William Lee Irwin III wrote: >> be found by this. There's also likely trouble with higher-order pages. On Tue, Jun 28, 2005 at 10:03:00AM +1000, Nick Piggin wrote: > There isn't because higher order pages aren't used for pagecache. hugetlbfs William Lee Irwin III wrote: >> page != *pagep won't be reliably tripped unless the pagecache >> modification has the appropriate memory barriers. On Tue, Jun 28, 2005 at 10:03:00AM +1000, Nick Piggin wrote: > There are appropriate memory barriers: the radix tree is > modified uner the rwlock/spinlock, and this function has > a memory barrier before testing page != *pagep. Someone else deal with this (paulus? anton? other arch maintainers?). William Lee Irwin III wrote: >> The lockless radix tree lookups are a harder problem than this, and >> the implementation didn't look promising. I have other problems to deal >> with so I'm not going to go very far into this. On Tue, Jun 28, 2005 at 10:03:00AM +1000, Nick Piggin wrote: > What's wrong with the lockless radix tree lookups? The above is as much as I wanted to go into it. I need to direct my capacity for the grunt work of devising adversary arguments elsewhere. William Lee Irwin III wrote: >> While I agree that locklessness is the right direction for the >> pagecache to go, this RFC seems to have too far to go to use it to >> conclude anything about the subject. On Tue, Jun 28, 2005 at 10:03:00AM +1000, Nick Piggin wrote: > You don't seem to have looked enough to conclude anything about it. You requested comments. I made some. Anyhow, my review has not been comprehensive. I stopped after the first few things I found that needed fixing. If others could deal with the rest of this, I'd be much obliged. -- wli -- 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: aart@kvack.org