From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: pagefault_disable (was Re: [patch 6/6] mm: fix pagecache write deadlocks) From: Peter Zijlstra In-Reply-To: <4533A411.2020207@yahoo.com.au> References: <20061013143516.15438.8802.sendpatchset@linux.site> <20061013143616.15438.77140.sendpatchset@linux.site> <1160912230.5230.23.camel@lappy> <20061015115656.GA25243@wotan.suse.de> <1160920269.5230.29.camel@lappy> <20061015141953.GC25243@wotan.suse.de> <1160927224.5230.36.camel@lappy> <20061015155727.GA539@wotan.suse.de> <1160928835.5230.41.camel@lappy> <4533A411.2020207@yahoo.com.au> Content-Type: text/plain Date: Mon, 16 Oct 2006 18:05:32 +0200 Message-Id: <1161014732.2096.9.camel@taijtu> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Nick Piggin Cc: Linux Memory Management , Linux Kernel , Andrew Morton , David Howells , Ingo Molnar List-ID: On Tue, 2006-10-17 at 01:24 +1000, Nick Piggin wrote: > (trimming cc list) > > Peter Zijlstra wrote: > > On Sun, 2006-10-15 at 17:57 +0200, Nick Piggin wrote: > > >>Hmm, but you may not be doing a copy*user within the kmap. And you may > >>want an atomic copy*user not within a kmap (maybe). > >> > >>I think it really would be more logical to do it in a wrapper function > >>pagefault_disable() pagefault_enable()? ;) > > > > > > I did that one first, but then noticed that most non trivial kmap_atomic > > implementations already did the inc_preempt_count()/dec_preempt_count() > > thing (except frv which did preempt_disable()/preempt_enable() ?) > > > > Anyway, here goes: > > > > Signed-off-by: Peter Zijlstra > > I think this is a good approach. The missed preempt checks could easily > have been causing scheduling delays because the usercopy can take up a > lot of kernel time. > > I don't know that the function should go in filemap.h... uaccess.h seems > more appropriate, and had thought the pagefault_disable() be calle > directly from within the copy_*_user_inatomic functions themselves, not > the filemap helper. > > Also, the rest of the kernel tree (mainly uaccess and futexes) should be > converted ;) Yeah, lotsa places to touch. > > Index: linux-2.6/mm/filemap.h > > =================================================================== > > --- linux-2.6.orig/mm/filemap.h 2006-10-14 20:20:20.000000000 +0200 > > +++ linux-2.6/mm/filemap.h 2006-10-15 17:17:45.000000000 +0200 > > @@ -21,6 +21,22 @@ __filemap_copy_from_user_iovec_inatomic( > > size_t bytes); > > > > /* > > + * By increasing the preempt_count we make sure the arch preempt > > + * handler bails out early, before taking any locks, so that the copy > > + * operation gets terminated early. > > + */ > > +pagefault_static inline void disable(void) > > +{ > > + inc_preempt_count(); I think we also need a barrier(); here. We need to make sure the preempt count is written to memory before we hit the fault handler. > > +} > > + > > +pagefault_static inline void enable(void) > > +{ > > + dec_preempt_count(); > > + preempt_check_resched(); > > +} > > Interesting prototype ;) Bah, sed magic gone awry ;-( -- 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