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[173.76.246.42]) by smtp.gmail.com with ESMTPSA id b66sm8011335qkf.64.2019.02.09.16.57.33 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Sat, 09 Feb 2019 16:57:34 -0800 (PST) Date: Sat, 9 Feb 2019 19:57:31 -0500 From: "Michael S. Tsirkin" To: Alexander Duyck Cc: 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 Message-ID: <20190209195325-mutt-send-email-mst@kernel.org> References: <20190204181118.12095.38300.stgit@localhost.localdomain> <20190204181558.12095.83484.stgit@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190204181558.12095.83484.stgit@localhost.localdomain> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 04, 2019 at 10:15:58AM -0800, Alexander Duyck wrote: > From: Alexander Duyck > > 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 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. > --- > 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 > 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.