From: "Michael S. Tsirkin" <mst@redhat.com> To: Nitesh Narayan Lal <nitesh@redhat.com> Cc: Alexander Duyck <alexander.duyck@gmail.com>, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, rkrcmar@redhat.com, alexander.h.duyck@linux.intel.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 12:41:08 -0500 Message-ID: <20190211123815-mutt-send-email-mst@kernel.org> (raw) In-Reply-To: <ac61d035-7c7b-bfec-c78b-b9387c40d3ea@redhat.com> On Mon, Feb 11, 2019 at 11:24:02AM -0500, Nitesh Narayan Lal wrote: > > On 2/11/19 9:17 AM, Michael S. Tsirkin wrote: > > On Mon, Feb 11, 2019 at 08:30:03AM -0500, Nitesh Narayan Lal wrote: > >> On 2/9/19 7:57 PM, Michael S. Tsirkin wrote: > >>> On Mon, Feb 04, 2019 at 10:15:58AM -0800, 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> > >>> Looks like this will be helpful whenever active free page > >>> hints are added. So I think it's a good idea to > >>> add a hook. > >>> > >>> However, could you split adding the hook to a separate > >>> patch from the KVM hypercall based implementation? > >>> > >>> Then e.g. Nilal's patches could reuse it too. > >> With the current design of my patch-set, if I use this hook to report > >> free pages. I will end up making redundant hints for the same pfns. > >> > >> This is because the pages once freed by the host, are returned back to > >> the buddy. > > Suggestions on how you'd like to fix this? You do need this if > > you introduce a size cut-off right? > > I do, there are two ways to go about it. > > One is to use this and have a flag in the page structure indicating > whether that page has been freed/used or not. Not sure what do you mean. The refcount does this right? > Though I am not sure if > this will be acceptable upstream. > Second is to find another place to invoke guest_free_page() post buddy > merging. Might be easier. > > > >>> > >>>> --- > >>>> 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); > >>>> } > >>>> if (max_order < MAX_ORDER) { > >>>> /* If we are here, it means order is >= pageblock_order. > >> -- > >> Regards > >> Nitesh > >> > > > > > -- > Regards > Nitesh >
next prev parent reply index 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 [this message] 2019-02-11 18:09 ` Nitesh Narayan Lal 2019-02-11 6:40 ` Aaron Lu 2019-02-11 15:58 ` Alexander Duyck 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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