From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: page fault scalability patch V16 [3/4]: Drop page_table_lock in handle_mm_fault From: Nick Piggin In-Reply-To: References: <41E5B7AD.40304@yahoo.com.au> <41E5BC60.3090309@yahoo.com.au> <20050113031807.GA97340@muc.de> <20050113180205.GA17600@muc.de> <20050114043944.GB41559@muc.de> <20050114170140.GB4634@muc.de> <41FF00CE.8060904@yahoo.com.au> <1107304296.5131.13.camel@npiggin-nld.site> Content-Type: text/plain Date: Wed, 02 Feb 2005 12:41:38 +1100 Message-Id: <1107308498.5131.28.camel@npiggin-nld.site> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Christoph Lameter Cc: Andi Kleen , Andrew Morton , torvalds@osdl.org, hugh@veritas.com, linux-mm@kvack.org, linux-ia64@vger.kernel.org, linux-kernel@vger.kernel.org, benh@kernel.crashing.org List-ID: On Tue, 2005-02-01 at 17:20 -0800, Christoph Lameter wrote: > On Wed, 2 Feb 2005, Nick Piggin wrote: > > > > The unmapping in rmap.c would change the pte. This would be discovered > > > after acquiring the spinlock later in do_wp_page. Which would then lead to > > > the operation being abandoned. > > Oh yes, but suppose your page_cache_get is happening at the same time > > as free_pages_check, after the page gets freed by the scanner? I can't > > actually think of anything that would cause a real problem (ie. not a > > debug check), off the top of my head. But can you say there _isn't_ > > anything? > > > > Regardless, it seems pretty dirty to me. But could possibly be made > > workable, of course. > > Would it make you feel better if we would move the spin_unlock back to the > prior position? This would ensure that the fallback case is exactly the > same. > Well yeah, but the interesting case is when that isn't a lock ;) I'm not saying what you've got is no good. I'm sure it would be fine for testing. And if it happens that we can do the "page_count doesn't mean anything after it has reached zero and been freed. Nor will it necessarily be zero when a new page is allocated" thing without many problems, then this may be a fine way to do it. I was just pointing out this could be a problem without putting a lot of thought into it... Find local movie times and trailers on Yahoo! Movies. http://au.movies.yahoo.com -- 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