From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 1 Apr 2004 16:52:16 -0800 From: Andrew Morton Subject: Re: [RFC][PATCH 1/3] radix priority search tree - objrmap complexity fix Message-Id: <20040401165216.40b9be98.akpm@osdl.org> In-Reply-To: <20040402001535.GG18585@dualathlon.random> References: <20040401020126.GW2143@dualathlon.random> <20040401133555.GC18585@dualathlon.random> <20040401150911.GI18585@dualathlon.random> <20040401151534.GJ18585@dualathlon.random> <20040402001535.GG18585@dualathlon.random> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Andrea Arcangeli Cc: hugh@veritas.com, vrajesh@umich.edu, linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: Andrea Arcangeli wrote: > > > @@ -149,8 +149,14 @@ int rw_swap_page_sync(int rw, swp_entry_ > > }; > > > > lock_page(page); > > - > > + /* > > + * This library call can be only used to do I/O > > + * on _private_ pages just allocated with alloc_pages(). > > + */ > > BUG_ON(page->mapping); > > + BUG_ON(PageSwapCache(page)); > > + BUG_ON(PageAnon(page)); > > + BUG_ON(PageLRU(page)); > > ret = add_to_page_cache(page, &swapper_space, entry.val, GFP_KERNEL); > > if (unlikely(ret)) { > > unlock_page(page); > > > the good thing is that I believe this fix will make it work with the -mm > writeback changes. However this fix now collides with anon-vma since > swapsuspend passes compound pages to rw_swap_page_sync and > add_to_page_cache overwrites page->private and the kernel crashes at the > next page_cache_get() since page->private is now the swap entry and not > a page_t pointer. Why do swapcache pages have their ->index in ->private? That should have been commented. (hugetlb pages are also added to pagecache, and they are compound, but the code looks OK). > So I guess I've a good reason now to giveup trying to > add the page to the swapcache, and to just fake the radix tree like I > did in my original fix. That way the page won't be swapcache either so I > don't even need to use get_page to avoid remove_exclusive_swap_page to > mess with it. The BUG_ON in radix_tree_tag_set() is a fairly arbitrary sanity check: "hey, why are you tagging a non-existent item?". We could simply replace it with a `return NULL;'? -- 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