| Message ID | 20190204181118.12095.38300.stgit@localhost.localdomain (mailing list archive) |
|---|---|
| Headers | show |
| Series | kvm: Report unused guest pages to host | expand |
On 2/4/19 1:15 PM, Alexander Duyck wrote: > This patch set provides a mechanism by which guests can notify the host of > pages that are not currently in use. Using this data a KVM host can more > easily balance memory workloads between guests and improve overall system > performance by avoiding unnecessary writing of unused pages to swap. > > In order to support this I have added a new hypercall to provided unused > page hints and made use of mechanisms currently used by PowerPC and s390 > architectures to provide those hints. To reduce the overhead of this call > I am only using it per huge page instead of of doing a notification per 4K > page. By doing this we can avoid the expense of fragmenting higher order > pages, and reduce overall cost for the hypercall as it will only be > performed once per huge page. > > Because we are limiting this to huge pages it was necessary to add a > secondary location where we make the call as the buddy allocator can merge > smaller pages into a higher order huge page. > > This approach is not usable in all cases. Specifically, when KVM direct > device assignment is used, the memory for a guest is permanently assigned > to physical pages in order to support DMA from the assigned device. In > this case we cannot give the pages back, so the hypercall is disabled by > the host. > > Another situation that can lead to issues is if the page were accessed > immediately after free. For example, if page poisoning is enabled the > guest will populate the page *after* freeing it. In this case it does not > make sense to provide a hint about the page being freed so we do not > perform the hypercalls from the guest if this functionality is enabled. > > My testing up till now has consisted of setting up 4 8GB VMs on a system > with 32GB of memory and 4GB of swap. To stress the memory on the system I > would run "memhog 8G" sequentially on each of the guests and observe how > long it took to complete the run. The observed behavior is that on the > systems with these patches applied in both the guest and on the host I was > able to complete the test with a time of 5 to 7 seconds per guest. On a > system without these patches the time ranged from 7 to 49 seconds per > guest. I am assuming the variability is due to time being spent writing > pages out to disk in order to free up space for the guest. Hi Alexander, Can you share the host memory usage before and after your run. (In both the cases with your patch-set and without your patch-set) > > --- > > Alexander Duyck (4): > madvise: Expose ability to set dontneed from kernel > kvm: Add host side support for free memory hints > kvm: Add guest side support for free memory hints > mm: Add merge page notifier > > > Documentation/virtual/kvm/cpuid.txt | 4 ++ > Documentation/virtual/kvm/hypercalls.txt | 14 ++++++++ > arch/x86/include/asm/page.h | 25 +++++++++++++++ > arch/x86/include/uapi/asm/kvm_para.h | 3 ++ > arch/x86/kernel/kvm.c | 51 ++++++++++++++++++++++++++++++ > arch/x86/kvm/cpuid.c | 6 +++- > arch/x86/kvm/x86.c | 35 +++++++++++++++++++++ > include/linux/gfp.h | 4 ++ > include/linux/mm.h | 2 + > include/uapi/linux/kvm_para.h | 1 + > mm/madvise.c | 13 +++++++- > mm/page_alloc.c | 2 + > 12 files changed, 158 insertions(+), 2 deletions(-) > > --
On Tue, 2019-02-05 at 12:25 -0500, Nitesh Narayan Lal wrote: > On 2/4/19 1:15 PM, Alexander Duyck wrote: > > This patch set provides a mechanism by which guests can notify the host of > > pages that are not currently in use. Using this data a KVM host can more > > easily balance memory workloads between guests and improve overall system > > performance by avoiding unnecessary writing of unused pages to swap. > > > > In order to support this I have added a new hypercall to provided unused > > page hints and made use of mechanisms currently used by PowerPC and s390 > > architectures to provide those hints. To reduce the overhead of this call > > I am only using it per huge page instead of of doing a notification per 4K > > page. By doing this we can avoid the expense of fragmenting higher order > > pages, and reduce overall cost for the hypercall as it will only be > > performed once per huge page. > > > > Because we are limiting this to huge pages it was necessary to add a > > secondary location where we make the call as the buddy allocator can merge > > smaller pages into a higher order huge page. > > > > This approach is not usable in all cases. Specifically, when KVM direct > > device assignment is used, the memory for a guest is permanently assigned > > to physical pages in order to support DMA from the assigned device. In > > this case we cannot give the pages back, so the hypercall is disabled by > > the host. > > > > Another situation that can lead to issues is if the page were accessed > > immediately after free. For example, if page poisoning is enabled the > > guest will populate the page *after* freeing it. In this case it does not > > make sense to provide a hint about the page being freed so we do not > > perform the hypercalls from the guest if this functionality is enabled. > > > > My testing up till now has consisted of setting up 4 8GB VMs on a system > > with 32GB of memory and 4GB of swap. To stress the memory on the system I > > would run "memhog 8G" sequentially on each of the guests and observe how > > long it took to complete the run. The observed behavior is that on the > > systems with these patches applied in both the guest and on the host I was > > able to complete the test with a time of 5 to 7 seconds per guest. On a > > system without these patches the time ranged from 7 to 49 seconds per > > guest. I am assuming the variability is due to time being spent writing > > pages out to disk in order to free up space for the guest. > > Hi Alexander, > > Can you share the host memory usage before and after your run. (In both > the cases with your patch-set and without your patch-set) Here are some snippets from the /proc/meminfo for the system both before and after the test. W/O patch -- Before -- MemTotal: 32881396 kB MemFree: 21363724 kB MemAvailable: 25891228 kB Buffers: 2276 kB Cached: 4760280 kB SwapCached: 0 kB Active: 7166952 kB Inactive: 1474980 kB Active(anon): 3893308 kB Inactive(anon): 8776 kB Active(file): 3273644 kB Inactive(file): 1466204 kB Unevictable: 16756 kB Mlocked: 16756 kB SwapTotal: 4194300 kB SwapFree: 4194300 kB Dirty: 29812 kB Writeback: 0 kB AnonPages: 3896540 kB Mapped: 75568 kB Shmem: 10044 kB -- After -- MemTotal: 32881396 kB MemFree: 194668 kB MemAvailable: 51356 kB Buffers: 24 kB Cached: 129036 kB SwapCached: 224396 kB Active: 27223304 kB Inactive: 2589736 kB Active(anon): 27220360 kB Inactive(anon): 2481592 kB Active(file): 2944 kB Inactive(file): 108144 kB Unevictable: 16756 kB Mlocked: 16756 kB SwapTotal: 4194300 kB SwapFree: 35616 kB Dirty: 0 kB Writeback: 0 kB AnonPages: 29476628 kB Mapped: 22820 kB Shmem: 5516 kB W/ patch -- Before -- MemTotal: 32881396 kB MemFree: 26618880 kB MemAvailable: 27056004 kB Buffers: 2276 kB Cached: 781496 kB SwapCached: 0 kB Active: 3309056 kB Inactive: 393796 kB Active(anon): 2932728 kB Inactive(anon): 8776 kB Active(file): 376328 kB Inactive(file): 385020 kB Unevictable: 16756 kB Mlocked: 16756 kB SwapTotal: 4194300 kB SwapFree: 4194300 kB Dirty: 96 kB Writeback: 0 kB AnonPages: 2935964 kB Mapped: 75428 kB Shmem: 10048 kB -- After -- MemTotal: 32881396 kB MemFree: 22677904 kB MemAvailable: 26543092 kB Buffers: 2276 kB Cached: 4205908 kB SwapCached: 0 kB Active: 3863016 kB Inactive: 3768596 kB Active(anon): 3437368 kB Inactive(anon): 8772 kB Active(file): 425648 kB Inactive(file): 3759824 kB Unevictable: 16756 kB Mlocked: 16756 kB SwapTotal: 4194300 kB SwapFree: 4194300 kB Dirty: 1336180 kB Writeback: 0 kB AnonPages: 3440528 kB Mapped: 74992 kB Shmem: 10044 kB
On 2/4/19 1:15 PM, Alexander Duyck wrote: > This patch set provides a mechanism by which guests can notify the host of > pages that are not currently in use. Using this data a KVM host can more > easily balance memory workloads between guests and improve overall system > performance by avoiding unnecessary writing of unused pages to swap. > > In order to support this I have added a new hypercall to provided unused > page hints and made use of mechanisms currently used by PowerPC and s390 > architectures to provide those hints. To reduce the overhead of this call > I am only using it per huge page instead of of doing a notification per 4K > page. By doing this we can avoid the expense of fragmenting higher order > pages, and reduce overall cost for the hypercall as it will only be > performed once per huge page. > > Because we are limiting this to huge pages it was necessary to add a > secondary location where we make the call as the buddy allocator can merge > smaller pages into a higher order huge page. > > This approach is not usable in all cases. Specifically, when KVM direct > device assignment is used, the memory for a guest is permanently assigned > to physical pages in order to support DMA from the assigned device. In > this case we cannot give the pages back, so the hypercall is disabled by > the host. > > Another situation that can lead to issues is if the page were accessed > immediately after free. For example, if page poisoning is enabled the > guest will populate the page *after* freeing it. In this case it does not > make sense to provide a hint about the page being freed so we do not > perform the hypercalls from the guest if this functionality is enabled. Hi Alexander, Did you get a chance to look at my v8 posting of Guest Free Page Hinting [1]? Considering both the solutions are trying to solve the same problem. It will be great if we can collaborate and come up with a unified solution. [1] https://lkml.org/lkml/2019/2/4/993 > > My testing up till now has consisted of setting up 4 8GB VMs on a system > with 32GB of memory and 4GB of swap. To stress the memory on the system I > would run "memhog 8G" sequentially on each of the guests and observe how > long it took to complete the run. The observed behavior is that on the > systems with these patches applied in both the guest and on the host I was > able to complete the test with a time of 5 to 7 seconds per guest. On a > system without these patches the time ranged from 7 to 49 seconds per > guest. I am assuming the variability is due to time being spent writing > pages out to disk in order to free up space for the guest. > > --- > > Alexander Duyck (4): > madvise: Expose ability to set dontneed from kernel > kvm: Add host side support for free memory hints > kvm: Add guest side support for free memory hints > mm: Add merge page notifier > > > Documentation/virtual/kvm/cpuid.txt | 4 ++ > Documentation/virtual/kvm/hypercalls.txt | 14 ++++++++ > arch/x86/include/asm/page.h | 25 +++++++++++++++ > arch/x86/include/uapi/asm/kvm_para.h | 3 ++ > arch/x86/kernel/kvm.c | 51 ++++++++++++++++++++++++++++++ > arch/x86/kvm/cpuid.c | 6 +++- > arch/x86/kvm/x86.c | 35 +++++++++++++++++++++ > include/linux/gfp.h | 4 ++ > include/linux/mm.h | 2 + > include/uapi/linux/kvm_para.h | 1 + > mm/madvise.c | 13 +++++++- > mm/page_alloc.c | 2 + > 12 files changed, 158 insertions(+), 2 deletions(-) > > --
On Thu, 2019-02-07 at 09:48 -0500, Nitesh Narayan Lal wrote: > On 2/4/19 1:15 PM, Alexander Duyck wrote: > > This patch set provides a mechanism by which guests can notify the host of > > pages that are not currently in use. Using this data a KVM host can more > > easily balance memory workloads between guests and improve overall system > > performance by avoiding unnecessary writing of unused pages to swap. > > > > In order to support this I have added a new hypercall to provided unused > > page hints and made use of mechanisms currently used by PowerPC and s390 > > architectures to provide those hints. To reduce the overhead of this call > > I am only using it per huge page instead of of doing a notification per 4K > > page. By doing this we can avoid the expense of fragmenting higher order > > pages, and reduce overall cost for the hypercall as it will only be > > performed once per huge page. > > > > Because we are limiting this to huge pages it was necessary to add a > > secondary location where we make the call as the buddy allocator can merge > > smaller pages into a higher order huge page. > > > > This approach is not usable in all cases. Specifically, when KVM direct > > device assignment is used, the memory for a guest is permanently assigned > > to physical pages in order to support DMA from the assigned device. In > > this case we cannot give the pages back, so the hypercall is disabled by > > the host. > > > > Another situation that can lead to issues is if the page were accessed > > immediately after free. For example, if page poisoning is enabled the > > guest will populate the page *after* freeing it. In this case it does not > > make sense to provide a hint about the page being freed so we do not > > perform the hypercalls from the guest if this functionality is enabled. > > Hi Alexander, > > Did you get a chance to look at my v8 posting of Guest Free Page Hinting > [1]? > Considering both the solutions are trying to solve the same problem. It > will be great if we can collaborate and come up with a unified solution. > > [1] https://lkml.org/lkml/2019/2/4/993 I haven't had a chance to review these yet. I'll try to take a look later today and provide review notes based on what I find. Thanks. - Alex
On Mon, Feb 04, 2019 at 10:15:33AM -0800, Alexander Duyck wrote: > This patch set provides a mechanism by which guests can notify the host of > pages that are not currently in use. Using this data a KVM host can more > easily balance memory workloads between guests and improve overall system > performance by avoiding unnecessary writing of unused pages to swap. There's an obvious overlap with Nilal's work and already merged Wei's work here. So please Cc people reviewing Nilal's and Wei's patches. > In order to support this I have added a new hypercall to provided unused > page hints and made use of mechanisms currently used by PowerPC and s390 > architectures to provide those hints. To reduce the overhead of this call > I am only using it per huge page instead of of doing a notification per 4K > page. By doing this we can avoid the expense of fragmenting higher order > pages, and reduce overall cost for the hypercall as it will only be > performed once per huge page. > > Because we are limiting this to huge pages it was necessary to add a > secondary location where we make the call as the buddy allocator can merge > smaller pages into a higher order huge page. > > This approach is not usable in all cases. Specifically, when KVM direct > device assignment is used, the memory for a guest is permanently assigned > to physical pages in order to support DMA from the assigned device. In > this case we cannot give the pages back, so the hypercall is disabled by > the host. > > Another situation that can lead to issues is if the page were accessed > immediately after free. For example, if page poisoning is enabled the > guest will populate the page *after* freeing it. In this case it does not > make sense to provide a hint about the page being freed so we do not > perform the hypercalls from the guest if this functionality is enabled. > > My testing up till now has consisted of setting up 4 8GB VMs on a system > with 32GB of memory and 4GB of swap. To stress the memory on the system I > would run "memhog 8G" sequentially on each of the guests and observe how > long it took to complete the run. The observed behavior is that on the > systems with these patches applied in both the guest and on the host I was > able to complete the test with a time of 5 to 7 seconds per guest. On a > system without these patches the time ranged from 7 to 49 seconds per > guest. I am assuming the variability is due to time being spent writing > pages out to disk in order to free up space for the guest. > > --- > > Alexander Duyck (4): > madvise: Expose ability to set dontneed from kernel > kvm: Add host side support for free memory hints > kvm: Add guest side support for free memory hints > mm: Add merge page notifier > > > Documentation/virtual/kvm/cpuid.txt | 4 ++ > Documentation/virtual/kvm/hypercalls.txt | 14 ++++++++ > arch/x86/include/asm/page.h | 25 +++++++++++++++ > arch/x86/include/uapi/asm/kvm_para.h | 3 ++ > arch/x86/kernel/kvm.c | 51 ++++++++++++++++++++++++++++++ > arch/x86/kvm/cpuid.c | 6 +++- > arch/x86/kvm/x86.c | 35 +++++++++++++++++++++ > include/linux/gfp.h | 4 ++ > include/linux/mm.h | 2 + > include/uapi/linux/kvm_para.h | 1 + > mm/madvise.c | 13 +++++++- > mm/page_alloc.c | 2 + > 12 files changed, 158 insertions(+), 2 deletions(-) > > --
This patch set provides a mechanism by which guests can notify the host of pages that are not currently in use. Using this data a KVM host can more easily balance memory workloads between guests and improve overall system performance by avoiding unnecessary writing of unused pages to swap. In order to support this I have added a new hypercall to provided unused page hints and made use of mechanisms currently used by PowerPC and s390 architectures to provide those hints. To reduce the overhead of this call I am only using it per huge page instead of of doing a notification per 4K page. By doing this we can avoid the expense of fragmenting higher order pages, and reduce overall cost for the hypercall as it will only be performed once per huge page. Because we are limiting this to huge pages it was necessary to add a secondary location where we make the call as the buddy allocator can merge smaller pages into a higher order huge page. This approach is not usable in all cases. Specifically, when KVM direct device assignment is used, the memory for a guest is permanently assigned to physical pages in order to support DMA from the assigned device. In this case we cannot give the pages back, so the hypercall is disabled by the host. Another situation that can lead to issues is if the page were accessed immediately after free. For example, if page poisoning is enabled the guest will populate the page *after* freeing it. In this case it does not make sense to provide a hint about the page being freed so we do not perform the hypercalls from the guest if this functionality is enabled. My testing up till now has consisted of setting up 4 8GB VMs on a system with 32GB of memory and 4GB of swap. To stress the memory on the system I would run "memhog 8G" sequentially on each of the guests and observe how long it took to complete the run. The observed behavior is that on the systems with these patches applied in both the guest and on the host I was able to complete the test with a time of 5 to 7 seconds per guest. On a system without these patches the time ranged from 7 to 49 seconds per guest. I am assuming the variability is due to time being spent writing pages out to disk in order to free up space for the guest. --- Alexander Duyck (4): madvise: Expose ability to set dontneed from kernel kvm: Add host side support for free memory hints kvm: Add guest side support for free memory hints mm: Add merge page notifier Documentation/virtual/kvm/cpuid.txt | 4 ++ Documentation/virtual/kvm/hypercalls.txt | 14 ++++++++ arch/x86/include/asm/page.h | 25 +++++++++++++++ arch/x86/include/uapi/asm/kvm_para.h | 3 ++ arch/x86/kernel/kvm.c | 51 ++++++++++++++++++++++++++++++ arch/x86/kvm/cpuid.c | 6 +++- arch/x86/kvm/x86.c | 35 +++++++++++++++++++++ include/linux/gfp.h | 4 ++ include/linux/mm.h | 2 + include/uapi/linux/kvm_para.h | 1 + mm/madvise.c | 13 +++++++- mm/page_alloc.c | 2 + 12 files changed, 158 insertions(+), 2 deletions(-) --