From mboxrd@z Thu Jan 1 00:00:00 1970 From: Martin Schwidefsky Subject: Re: [patch 4/6] Guest page hinting: writable page table entries. Date: Wed, 1 Apr 2009 16:36:58 +0200 Message-ID: <20090401163658.60f851ed@skybase> References: <20090327150905.819861420@de.ibm.com> <20090327151012.398894143@de.ibm.com> <49D36B4E.7000702@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <49D36B4E.7000702@redhat.com> Sender: owner-linux-mm@kvack.org To: Rik van Riel Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, virtualization@lists.osdl.org, frankeh@watson.ibm.com, akpm@osdl.org, nickpiggin@yahoo.com.au, hugh@veritas.com List-Id: virtualization@lists.linuxfoundation.org On Wed, 01 Apr 2009 09:25:34 -0400 Rik van Riel wrote: > Martin Schwidefsky wrote: > > This code has me stumped. Does it mean that if a page already > has the PageWritable bit set (and count_ok stays 0), we will > always mark the page as volatile? > > How does that work out on !s390? No, we will not always mark the page as volatile. If PG_writable is already set count_ok will stay 0 and a call to page_make_volatile is done. This differs from page_set_volatile as it repeats all the required checks, then calls page_set_volatile with a PageWritable(page) as second argument. What state the page will get depends on the architecture definition of page_set_volatile. For s390 this will do a state transition to potentially volatile as the PG_writable bit is set. On architecture that cannot check the dirty bit on a physical page basis you need to make the page stable. > > /** > > + * __page_check_writable() - check page state for new writable pte > > + * > > + * @page: the page the new writable pte refers to > > + * @pte: the new writable pte > > + */ > > +void __page_check_writable(struct page *page, pte_t pte, unsigned int offset) > > +{ > > + int count_ok = 0; > > + > > + preempt_disable(); > > + while (page_test_set_state_change(page)) > > + cpu_relax(); > > + > > + if (!TestSetPageWritable(page)) { > > + count_ok = check_counts(page, offset); > > + if (check_bits(page) && count_ok) > > + page_set_volatile(page, 1); > > + else > > + /* > > + * If two processes create a write mapping at the > > + * same time check_counts will return false or if > > + * the page is currently isolated from the LRU > > + * check_bits will return false but the page might > > + * be in volatile state. > > + * We have to take care about the dirty bit so the > > + * only option left is to make the page stable but > > + * we can try to make it volatile a bit later. > > + */ > > + page_set_stable_if_present(page); > > + } > > + page_clear_state_change(page); > > + if (!count_ok) > > + page_make_volatile(page, 1); > > + preempt_enable(); > > +} > > +EXPORT_SYMBOL(__page_check_writable); > > -- blue skies, Martin. "Reality continues to ruin my life." - Calvin. -- 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