From: Alexander Duyck <alexander.h.duyck@linux.intel.com> To: Aaron Lu <aaron.lwe@gmail.com>, Alexander Duyck <alexander.duyck@gmail.com>, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: rkrcmar@redhat.com, x86@kernel.org, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, pbonzini@redhat.com, tglx@linutronix.de, akpm@linux-foundation.org Subject: Re: [RFC PATCH 4/4] mm: Add merge page notifier Date: Mon, 11 Feb 2019 07:58:28 -0800 [thread overview] Message-ID: <a5b698b0f85667dba9b949dcb6e65a0d806669de.camel@linux.intel.com> (raw) In-Reply-To: <5e6d22b2-0f14-43eb-846b-a940e629c02b@gmail.com> On Mon, 2019-02-11 at 14:40 +0800, Aaron Lu wrote: > On 2019/2/5 2:15, Alexander Duyck wrote: > > From: Alexander Duyck <alexander.h.duyck@linux.intel.com> > > > > Because the implementation was limiting itself to only providing hints on > > pages huge TLB order sized or larger we introduced the possibility for free > > pages to slip past us because they are freed as something less then > > huge TLB in size and aggregated with buddies later. > > > > To address that I am adding a new call arch_merge_page which is called > > after __free_one_page has merged a pair of pages to create a higher order > > page. By doing this I am able to fill the gap and provide full coverage for > > all of the pages huge TLB order or larger. > > > > Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com> > > --- > > arch/x86/include/asm/page.h | 12 ++++++++++++ > > arch/x86/kernel/kvm.c | 28 ++++++++++++++++++++++++++++ > > include/linux/gfp.h | 4 ++++ > > mm/page_alloc.c | 2 ++ > > 4 files changed, 46 insertions(+) > > > > diff --git a/arch/x86/include/asm/page.h b/arch/x86/include/asm/page.h > > index 4487ad7a3385..9540a97c9997 100644 > > --- a/arch/x86/include/asm/page.h > > +++ b/arch/x86/include/asm/page.h > > @@ -29,6 +29,18 @@ static inline void arch_free_page(struct page *page, unsigned int order) > > if (static_branch_unlikely(&pv_free_page_hint_enabled)) > > __arch_free_page(page, order); > > } > > + > > +struct zone; > > + > > +#define HAVE_ARCH_MERGE_PAGE > > +void __arch_merge_page(struct zone *zone, struct page *page, > > + unsigned int order); > > +static inline void arch_merge_page(struct zone *zone, struct page *page, > > + unsigned int order) > > +{ > > + if (static_branch_unlikely(&pv_free_page_hint_enabled)) > > + __arch_merge_page(zone, page, order); > > +} > > #endif > > > > #include <linux/range.h> > > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c > > index 09c91641c36c..957bb4f427bb 100644 > > --- a/arch/x86/kernel/kvm.c > > +++ b/arch/x86/kernel/kvm.c > > @@ -785,6 +785,34 @@ void __arch_free_page(struct page *page, unsigned int order) > > PAGE_SIZE << order); > > } > > > > +void __arch_merge_page(struct zone *zone, struct page *page, > > + unsigned int order) > > +{ > > + /* > > + * The merging logic has merged a set of buddies up to the > > + * KVM_PV_UNUSED_PAGE_HINT_MIN_ORDER. Since that is the case, take > > + * advantage of this moment to notify the hypervisor of the free > > + * memory. > > + */ > > + if (order != KVM_PV_UNUSED_PAGE_HINT_MIN_ORDER) > > + return; > > + > > + /* > > + * Drop zone lock while processing the hypercall. This > > + * should be safe as the page has not yet been added > > + * to the buddy list as of yet and all the pages that > > + * were merged have had their buddy/guard flags cleared > > + * and their order reset to 0. > > + */ > > + spin_unlock(&zone->lock); > > + > > + kvm_hypercall2(KVM_HC_UNUSED_PAGE_HINT, page_to_phys(page), > > + PAGE_SIZE << order); > > + > > + /* reacquire lock and resume freeing memory */ > > + spin_lock(&zone->lock); > > +} > > + > > #ifdef CONFIG_PARAVIRT_SPINLOCKS > > > > /* Kick a cpu by its apicid. Used to wake up a halted vcpu */ > > diff --git a/include/linux/gfp.h b/include/linux/gfp.h > > index fdab7de7490d..4746d5560193 100644 > > --- a/include/linux/gfp.h > > +++ b/include/linux/gfp.h > > @@ -459,6 +459,10 @@ static inline struct zonelist *node_zonelist(int nid, gfp_t flags) > > #ifndef HAVE_ARCH_FREE_PAGE > > static inline void arch_free_page(struct page *page, int order) { } > > #endif > > +#ifndef HAVE_ARCH_MERGE_PAGE > > +static inline void > > +arch_merge_page(struct zone *zone, struct page *page, int order) { } > > +#endif > > #ifndef HAVE_ARCH_ALLOC_PAGE > > static inline void arch_alloc_page(struct page *page, int order) { } > > #endif > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > index c954f8c1fbc4..7a1309b0b7c5 100644 > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -913,6 +913,8 @@ static inline void __free_one_page(struct page *page, > > page = page + (combined_pfn - pfn); > > pfn = combined_pfn; > > order++; > > + > > + arch_merge_page(zone, page, order); > > Not a proper place AFAICS. > > Assume we have an order-8 page being sent here for merge and its order-8 > buddy is also free, then order++ became 9 and arch_merge_page() will do > the hint to host on this page as an order-9 page, no problem so far. > Then the next round, assume the now order-9 page's buddy is also free, > order++ will become 10 and arch_merge_page() will again hint to host on > this page as an order-10 page. The first hint to host became redundant. Actually the problem is even worse the other way around. My concern was pages being incrementally freed. With this setup I can catch when we have crossed the threshold from order 8 to 9, and specifically for that case provide the hint. This allows me to ignore orders above and below 9. If I move the hint to the spot after the merging I have no way of telling if I have hinted the page as a lower order or not. As such I will hint if it is merged up to orders 9 or greater. So for example if it merges up to order 9 and stops there then done_merging will report an order 9 page, then if another page is freed and merged with this up to order 10 you would be hinting on order 10. By placing the function here I can guarantee that no more than 1 hint is provided per 2MB page. > I think the proper place is after the done_merging tag. > > BTW, with arch_merge_page() at the proper place, I don't think patch3/4 > is necessary - any freed page will go through merge anyway, we won't > lose any hint opportunity. Or do I miss anything? You can refer to my comment above. What I want to avoid is us hinting a page multiple times if we aren't using MAX_ORDER - 1 as the limit. What I am avoiding by placing this where I did is us doing a hint on orders greater than our target hint order. So with this way I only perform one hint per 2MB page, otherwise I would be performing multiple hints per 2MB page as every order above that would also trigger hints.
next prev parent reply other threads:[~2019-02-11 15:58 UTC|newest] Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-02-04 18:15 [RFC PATCH 0/4] kvm: Report unused guest pages to host Alexander Duyck 2019-02-04 18:15 ` [RFC PATCH 1/4] madvise: Expose ability to set dontneed from kernel Alexander Duyck 2019-02-04 18:15 ` [RFC PATCH 2/4] kvm: Add host side support for free memory hints Alexander Duyck 2019-02-10 0:44 ` Michael S. Tsirkin 2019-02-11 17:34 ` Alexander Duyck 2019-02-11 17:36 ` Michael S. Tsirkin 2019-02-11 17:41 ` Dave Hansen 2019-02-11 17:48 ` Michael S. Tsirkin 2019-02-11 18:30 ` Alexander Duyck 2019-02-11 19:24 ` Michael S. Tsirkin 2019-02-04 18:15 ` [RFC PATCH 3/4] kvm: Add guest " Alexander Duyck 2019-02-04 19:44 ` Dave Hansen 2019-02-04 20:42 ` Alexander Duyck 2019-02-04 23:00 ` Nadav Amit 2019-02-04 23:37 ` Alexander Duyck 2019-02-05 0:03 ` Nadav Amit 2019-02-05 0:16 ` Alexander Duyck 2019-02-05 1:46 ` Nadav Amit 2019-02-05 18:09 ` Alexander Duyck 2019-02-07 18:21 ` Luiz Capitulino 2019-02-07 18:44 ` Alexander Duyck 2019-02-07 20:02 ` Luiz Capitulino 2019-02-08 21:05 ` Nitesh Narayan Lal 2019-02-08 21:31 ` Alexander Duyck 2019-02-10 0:49 ` Michael S. Tsirkin 2019-02-11 16:31 ` Alexander Duyck 2019-02-11 17:36 ` Michael S. Tsirkin 2019-02-11 18:10 ` Alexander Duyck 2019-02-11 19:54 ` Michael S. Tsirkin 2019-02-11 21:00 ` Alexander Duyck 2019-02-11 22:52 ` Michael S. Tsirkin [not found] ` <94462313ccd927d25675f69de459456cf066c1a2.camel@linux.intel.com> 2019-02-12 0:34 ` Michael S. Tsirkin 2019-02-11 17:48 ` Dave Hansen 2019-02-11 17:58 ` Michael S. Tsirkin 2019-02-11 18:19 ` Dave Hansen 2019-02-11 19:56 ` Michael S. Tsirkin 2019-02-04 18:15 ` [RFC PATCH 4/4] mm: Add merge page notifier Alexander Duyck 2019-02-04 19:40 ` Dave Hansen 2019-02-04 19:51 ` Alexander Duyck 2019-02-10 0:57 ` Michael S. Tsirkin 2019-02-11 13:30 ` Nitesh Narayan Lal 2019-02-11 14:17 ` Michael S. Tsirkin 2019-02-11 16:24 ` Nitesh Narayan Lal 2019-02-11 17:41 ` Michael S. Tsirkin 2019-02-11 18:09 ` Nitesh Narayan Lal 2019-02-11 6:40 ` Aaron Lu 2019-02-11 15:58 ` Alexander Duyck [this message] 2019-02-12 2:09 ` Aaron Lu 2019-02-12 17:20 ` Alexander Duyck 2019-02-04 18:19 ` [RFC PATCH QEMU] i386/kvm: Enable paravirtual unused page hint mechanism Alexander Duyck 2019-02-05 17:25 ` [RFC PATCH 0/4] kvm: Report unused guest pages to host Nitesh Narayan Lal 2019-02-05 18:43 ` Alexander Duyck 2019-02-07 14:48 ` Nitesh Narayan Lal 2019-02-07 16:56 ` Alexander Duyck 2019-02-10 0:51 ` Michael S. Tsirkin
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