From: Andrea Arcangeli <aarcange@redhat.com> To: Dave Hansen <dave.hansen@intel.com> Cc: David Hildenbrand <david@redhat.com>, "Li, Liang Z" <liang.z.li@intel.com>, "kvm@vger.kernel.org" <kvm@vger.kernel.org>, "mhocko@suse.com" <mhocko@suse.com>, "mst@redhat.com" <mst@redhat.com>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, "linux-mm@kvack.org" <linux-mm@kvack.org>, "dgilbert@redhat.com" <dgilbert@redhat.com>, "pbonzini@redhat.com" <pbonzini@redhat.com>, "akpm@linux-foundation.org" <akpm@linux-foundation.org>, "virtualization@lists.linux-foundation.org" <virtualization@lists.linux-foundation.org>, "kirill.shutemov@linux.intel.com" <kirill.shutemov@linux.intel.com> Subject: Re: [Qemu-devel] [PATCH kernel v5 0/5] Extend virtio-balloon for fast (de)inflating & fast live migration Date: Wed, 7 Dec 2016 19:58:50 +0100 [thread overview] Message-ID: <20161207185850.GF28786@redhat.com> (raw) In-Reply-To: <3954fe69-15ac-43eb-e14b-e2bfe976be33@intel.com> On Wed, Dec 07, 2016 at 10:44:31AM -0800, Dave Hansen wrote: > On 12/07/2016 10:38 AM, Andrea Arcangeli wrote: > >> > and leaves room for the bitmap size to be encoded as well, if we decide > >> > we need a bitmap in the future. > > How would a bitmap ever be useful with very large page-order? > > Please, guys. Read the patches. *Please*. I did read the code but you didn't answer my question. Why should a feature exist in the code that will never be useful. Why do you think we could ever decide we'll need the bitmap in the future for high order pages? > The current code doesn't even _use_ a bitmap. It's not using it right now, my question is exactly when it will ever use it? Leaving the bitmap only for order 0 allocations when you already wiped all high pages orders from the buddy, doesn't seem very good idea overall as the chance you got order 0 pages with close physical address doesn't seem very high. It would be high if the loop that eat into every possible higher order didn't run first, but such loop just run and already wiped everything. Also note, we need to call compaction very aggressive before falling back from order 9 down to order 8. Ideally we should never use the page_shift = PAGE_SHIFT case at all! Which leaves the bitmap as best as an optimization for something that is suboptimal case already. If the bitmap starts to payoff it means the admin did a mistake and shrunk the guest too much.
WARNING: multiple messages have this Message-ID (diff)
From: Andrea Arcangeli <aarcange@redhat.com> To: Dave Hansen <dave.hansen@intel.com> Cc: David Hildenbrand <david@redhat.com>, "Li, Liang Z" <liang.z.li@intel.com>, "kvm@vger.kernel.org" <kvm@vger.kernel.org>, "mhocko@suse.com" <mhocko@suse.com>, "mst@redhat.com" <mst@redhat.com>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, "linux-mm@kvack.org" <linux-mm@kvack.org>, "dgilbert@redhat.com" <dgilbert@redhat.com>, "pbonzini@redhat.com" <pbonzini@redhat.com>, "akpm@linux-foundation.org" <akpm@linux-foundation.org>, "virtualization@lists.linux-foundation.org" <virtualization@lists.linux-foundation.org>, "kirill.shutemov@linux.intel.com" <kirill.shutemov@linux.intel.com> Subject: Re: [Qemu-devel] [PATCH kernel v5 0/5] Extend virtio-balloon for fast (de)inflating & fast live migration Date: Wed, 7 Dec 2016 19:58:50 +0100 [thread overview] Message-ID: <20161207185850.GF28786@redhat.com> (raw) In-Reply-To: <3954fe69-15ac-43eb-e14b-e2bfe976be33@intel.com> On Wed, Dec 07, 2016 at 10:44:31AM -0800, Dave Hansen wrote: > On 12/07/2016 10:38 AM, Andrea Arcangeli wrote: > >> > and leaves room for the bitmap size to be encoded as well, if we decide > >> > we need a bitmap in the future. > > How would a bitmap ever be useful with very large page-order? > > Please, guys. Read the patches. *Please*. I did read the code but you didn't answer my question. Why should a feature exist in the code that will never be useful. Why do you think we could ever decide we'll need the bitmap in the future for high order pages? > The current code doesn't even _use_ a bitmap. It's not using it right now, my question is exactly when it will ever use it? Leaving the bitmap only for order 0 allocations when you already wiped all high pages orders from the buddy, doesn't seem very good idea overall as the chance you got order 0 pages with close physical address doesn't seem very high. It would be high if the loop that eat into every possible higher order didn't run first, but such loop just run and already wiped everything. Also note, we need to call compaction very aggressive before falling back from order 9 down to order 8. Ideally we should never use the page_shift = PAGE_SHIFT case at all! Which leaves the bitmap as best as an optimization for something that is suboptimal case already. If the bitmap starts to payoff it means the admin did a mistake and shrunk the guest too much. -- 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: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2016-12-07 18:58 UTC|newest] Thread overview: 165+ messages / expand[flat|nested] mbox.gz Atom feed top 2016-11-30 8:43 [PATCH kernel v5 0/5] Extend virtio-balloon for fast (de)inflating & fast live migration Liang Li 2016-11-30 8:43 ` [Qemu-devel] " Liang Li 2016-11-30 8:43 ` Liang Li 2016-11-30 8:43 ` [PATCH kernel v5 1/5] virtio-balloon: rework deflate to add page to a list Liang Li 2016-11-30 8:43 ` Liang Li 2016-11-30 8:43 ` [Qemu-devel] " Liang Li 2016-11-30 8:43 ` Liang Li 2016-11-30 8:43 ` [PATCH kernel v5 2/5] virtio-balloon: define new feature bit and head struct Liang Li 2016-11-30 8:43 ` Liang Li 2016-11-30 8:43 ` [Qemu-devel] " Liang Li 2016-11-30 8:43 ` Liang Li 2016-11-30 8:43 ` [PATCH kernel v5 3/5] virtio-balloon: speed up inflate/deflate process Liang Li 2016-11-30 8:43 ` [Qemu-devel] " Liang Li 2016-11-30 8:43 ` Liang Li 2016-11-30 8:43 ` Liang Li 2016-11-30 8:43 ` [PATCH kernel v5 4/5] virtio-balloon: define flags and head for host request vq Liang Li 2016-11-30 8:43 ` [Qemu-devel] " Liang Li 2016-11-30 8:43 ` Liang Li 2016-11-30 8:43 ` Liang Li 2016-11-30 8:43 ` [PATCH kernel v5 5/5] virtio-balloon: tell host vm's unused page info Liang Li 2016-11-30 8:43 ` Liang Li 2016-11-30 8:43 ` [Qemu-devel] " Liang Li 2016-11-30 8:43 ` Liang Li 2016-11-30 19:15 ` Dave Hansen 2016-11-30 19:15 ` Dave Hansen 2016-11-30 19:15 ` [Qemu-devel] " Dave Hansen 2016-11-30 19:15 ` Dave Hansen 2016-12-04 13:13 ` Li, Liang Z 2016-12-04 13:13 ` Li, Liang Z 2016-12-04 13:13 ` [Qemu-devel] " Li, Liang Z 2016-12-04 13:13 ` Li, Liang Z 2016-12-05 17:22 ` Dave Hansen 2016-12-05 17:22 ` [Qemu-devel] " Dave Hansen 2016-12-05 17:22 ` Dave Hansen 2016-12-05 17:22 ` Dave Hansen 2016-12-06 4:47 ` Li, Liang Z 2016-12-06 4:47 ` [Qemu-devel] " Li, Liang Z 2016-12-06 4:47 ` Li, Liang Z 2016-12-06 4:47 ` Li, Liang Z 2016-12-06 8:40 ` [PATCH kernel v5 0/5] Extend virtio-balloon for fast (de)inflating & fast live migration David Hildenbrand 2016-12-06 8:40 ` [Qemu-devel] " David Hildenbrand 2016-12-06 8:40 ` David Hildenbrand 2016-12-06 8:40 ` David Hildenbrand 2016-12-07 13:35 ` Li, Liang Z 2016-12-07 13:35 ` [Qemu-devel] " Li, Liang Z 2016-12-07 13:35 ` Li, Liang Z 2016-12-07 13:35 ` Li, Liang Z 2016-12-07 15:34 ` Dave Hansen 2016-12-07 15:34 ` [Qemu-devel] " Dave Hansen 2016-12-07 15:34 ` Dave Hansen 2016-12-09 3:09 ` Li, Liang Z 2016-12-09 3:09 ` [Qemu-devel] " Li, Liang Z 2016-12-09 3:09 ` Li, Liang Z 2016-12-09 3:09 ` Li, Liang Z 2016-12-09 3:09 ` Li, Liang Z 2016-12-07 15:34 ` Dave Hansen 2016-12-07 15:42 ` David Hildenbrand 2016-12-07 15:42 ` [Qemu-devel] " David Hildenbrand 2016-12-07 15:42 ` David Hildenbrand 2016-12-07 15:45 ` Dave Hansen 2016-12-07 15:45 ` [Qemu-devel] " Dave Hansen 2016-12-07 15:45 ` Dave Hansen 2016-12-07 15:45 ` Dave Hansen 2016-12-07 16:21 ` David Hildenbrand 2016-12-07 16:21 ` [Qemu-devel] " David Hildenbrand 2016-12-07 16:21 ` David Hildenbrand 2016-12-07 16:21 ` David Hildenbrand 2016-12-07 16:57 ` Dave Hansen 2016-12-07 16:57 ` Dave Hansen 2016-12-07 16:57 ` [Qemu-devel] " Dave Hansen 2016-12-07 16:57 ` Dave Hansen 2016-12-07 18:38 ` [Qemu-devel] " Andrea Arcangeli 2016-12-07 18:38 ` Andrea Arcangeli 2016-12-07 18:38 ` Andrea Arcangeli 2016-12-07 18:38 ` Andrea Arcangeli 2016-12-07 18:44 ` Dave Hansen 2016-12-07 18:44 ` Dave Hansen 2016-12-07 18:44 ` Dave Hansen 2016-12-07 18:44 ` Dave Hansen 2016-12-07 18:58 ` Andrea Arcangeli 2016-12-07 18:58 ` Andrea Arcangeli [this message] 2016-12-07 18:58 ` Andrea Arcangeli 2016-12-07 18:58 ` Andrea Arcangeli 2016-12-07 19:54 ` Dave Hansen 2016-12-07 19:54 ` Dave Hansen 2016-12-07 19:54 ` Dave Hansen 2016-12-07 19:54 ` Dave Hansen 2016-12-07 20:28 ` Andrea Arcangeli 2016-12-07 20:28 ` Andrea Arcangeli 2016-12-07 20:28 ` Andrea Arcangeli 2016-12-07 20:28 ` Andrea Arcangeli 2016-12-09 4:45 ` Li, Liang Z 2016-12-09 4:45 ` Li, Liang Z 2016-12-09 4:45 ` Li, Liang Z 2016-12-09 4:45 ` Li, Liang Z 2016-12-09 4:53 ` Dave Hansen 2016-12-09 4:53 ` Dave Hansen 2016-12-09 4:53 ` Dave Hansen 2016-12-09 4:53 ` Dave Hansen 2016-12-09 5:35 ` Li, Liang Z 2016-12-09 5:35 ` Li, Liang Z 2016-12-09 5:35 ` Li, Liang Z 2016-12-09 5:35 ` Li, Liang Z 2016-12-09 16:42 ` Andrea Arcangeli 2016-12-09 16:42 ` Andrea Arcangeli 2016-12-09 16:42 ` Andrea Arcangeli 2016-12-09 16:42 ` Andrea Arcangeli 2016-12-14 8:20 ` Li, Liang Z 2016-12-14 8:20 ` Li, Liang Z 2016-12-14 8:20 ` Li, Liang Z 2016-12-14 8:20 ` Li, Liang Z 2016-12-14 8:59 ` Li, Liang Z 2016-12-14 8:59 ` Li, Liang Z 2016-12-14 8:59 ` Li, Liang Z 2016-12-14 8:59 ` Li, Liang Z 2016-12-15 15:34 ` Dave Hansen 2016-12-15 15:34 ` Dave Hansen 2016-12-15 15:34 ` Dave Hansen 2016-12-15 15:34 ` Dave Hansen 2016-12-15 15:54 ` Michael S. Tsirkin 2016-12-15 15:54 ` Michael S. Tsirkin 2016-12-15 15:54 ` Michael S. Tsirkin 2016-12-15 15:54 ` Michael S. Tsirkin 2016-12-16 1:12 ` Li, Liang Z 2016-12-16 1:12 ` Li, Liang Z 2016-12-16 1:12 ` Li, Liang Z 2016-12-16 1:12 ` Li, Liang Z 2016-12-16 15:40 ` Andrea Arcangeli 2016-12-16 15:40 ` Andrea Arcangeli 2016-12-16 15:40 ` Andrea Arcangeli 2016-12-17 11:56 ` Li, Liang Z 2016-12-17 11:56 ` Li, Liang Z 2016-12-17 11:56 ` Li, Liang Z 2016-12-17 11:56 ` Li, Liang Z 2016-12-16 15:40 ` Andrea Arcangeli 2016-12-16 0:48 ` Li, Liang Z 2016-12-16 0:48 ` Li, Liang Z 2016-12-16 0:48 ` Li, Liang Z 2016-12-16 0:48 ` Li, Liang Z 2016-12-16 1:09 ` Dave Hansen 2016-12-16 1:09 ` Dave Hansen 2016-12-16 1:09 ` Dave Hansen 2016-12-16 1:09 ` Dave Hansen 2016-12-16 1:38 ` Li, Liang Z 2016-12-16 1:38 ` Li, Liang Z 2016-12-16 1:38 ` Li, Liang Z 2016-12-16 1:38 ` Li, Liang Z 2016-12-16 1:40 ` Dave Hansen 2016-12-16 1:40 ` Dave Hansen 2016-12-16 1:40 ` Dave Hansen 2016-12-16 1:40 ` Dave Hansen 2016-12-16 1:43 ` Li, Liang Z 2016-12-16 1:43 ` Li, Liang Z 2016-12-16 1:43 ` Li, Liang Z 2016-12-16 1:43 ` Li, Liang Z 2016-12-16 16:01 ` Andrea Arcangeli 2016-12-16 16:01 ` Andrea Arcangeli 2016-12-16 16:01 ` Andrea Arcangeli 2016-12-16 16:01 ` Andrea Arcangeli 2016-12-17 12:39 ` Li, Liang Z 2016-12-17 12:39 ` Li, Liang Z 2016-12-17 12:39 ` Li, Liang Z 2016-12-17 12:39 ` Li, Liang Z 2016-12-07 15:42 ` David Hildenbrand 2016-12-07 13:35 ` Li, Liang Z
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