On Wed, Jul 24, 2019 at 02:40:02PM -0400, Nitesh Narayan Lal wrote: > > On 7/24/19 12:54 PM, Alexander Duyck wrote: > > This series provides an asynchronous means of hinting to a hypervisor > > that a guest page is no longer in use and can have the data associated > > with it dropped. To do this I have implemented functionality that allows > > for what I am referring to as page hinting > > > > The functionality for this is fairly simple. When enabled it will allocate > > statistics to track the number of hinted pages in a given free area. When > > the number of free pages exceeds this value plus a high water value, > > currently 32, > Shouldn't we configure this to a lower number such as 16? > > it will begin performing page hinting which consists of > > pulling pages off of free list and placing them into a scatter list. The > > scatterlist is then given to the page hinting device and it will perform > > the required action to make the pages "hinted", in the case of > > virtio-balloon this results in the pages being madvised as MADV_DONTNEED > > and as such they are forced out of the guest. After this they are placed > > back on the free list, and an additional bit is added if they are not > > merged indicating that they are a hinted buddy page instead of a standard > > buddy page. The cycle then repeats with additional non-hinted pages being > > pulled until the free areas all consist of hinted pages. > > > > I am leaving a number of things hard-coded such as limiting the lowest > > order processed to PAGEBLOCK_ORDER, > Have you considered making this option configurable at the compile time? > > and have left it up to the guest to > > determine what the limit is on how many pages it wants to allocate to > > process the hints. > It might make sense to set the number of pages to be hinted at a time from the > hypervisor. > > > > My primary testing has just been to verify the memory is being freed after > > allocation by running memhog 79g on a 80g guest and watching the total > > free memory via /proc/meminfo on the host. With this I have verified most > > of the memory is freed after each iteration. As far as performance I have > > been mainly focusing on the will-it-scale/page_fault1 test running with > > 16 vcpus. With that I have seen at most a 2% difference between the base > > kernel without these patches and the patches with virtio-balloon disabled. > > With the patches and virtio-balloon enabled with hinting the results > > largely depend on the host kernel. On a 3.10 RHEL kernel I saw up to a 2% > > drop in performance as I approached 16 threads, > I think this is acceptable. > > however on the the lastest > > linux-next kernel I saw roughly a 4% to 5% improvement in performance for > > all tests with 8 or more threads. > Do you mean that with your patches the will-it-scale/page_fault1 numbers were > better by 4-5% over an unmodified kernel? > > I believe the difference seen is due to > > the overhead for faulting pages back into the guest and zeroing of memory. > It may also make sense to test these patches with netperf to observe how much > performance drop it is introducing. > > Patch 4 is a bit on the large side at about 600 lines of change, however > > I really didn't see a good way to break it up since each piece feeds into > > the next. So I couldn't add the statistics by themselves as it didn't > > really make sense to add them without something that will either read or > > increment/decrement them, or add the Hinted state without something that > > would set/unset it. As such I just ended up adding the entire thing as > > one patch. It makes it a bit bigger but avoids the issues in the previous > > set where I was referencing things before they had been added. > > > > Changes from the RFC: > > https://lore.kernel.org/lkml/20190530215223.13974.22445.stgit@localhost.localdomain/ > > Moved aeration requested flag out of aerator and into zone->flags. > > Moved bounary out of free_area and into local variables for aeration. > > Moved aeration cycle out of interrupt and into workqueue. > > Left nr_free as total pages instead of splitting it between raw and aerated. > > Combined size and physical address values in virtio ring into one 64b value. > > > > Changes from v1: > > https://lore.kernel.org/lkml/20190619222922.1231.27432.stgit@localhost.localdomain/ > > Dropped "waste page treatment" in favor of "page hinting" > We may still have to try and find a better name for virtio-balloon side changes. > As "FREE_PAGE_HINT" and "PAGE_HINTING" are still confusing. Right. In fact I'm not sure why should these be called hints at all. VIRTIO_BALLOON_F_FREE_PAGE_HINT is a hint because pages might no longer be free by the time they are reported. I think of this one as a free page reporting capability. I don't really mind how are internal kernel functions called, but I think for virtio uapi things that's a better name. > > Renamed files and functions from "aeration" to "page_hinting" > > Moved from page->lru list to scatterlist > > Replaced wait on refcnt in shutdown with RCU and cancel_delayed_work_sync > > Virtio now uses scatterlist directly instead of intermedate array > > Moved stats out of free_area, now in seperate area and pointed to from zone > > Merged patch 5 into patch 4 to improve reviewability > > Updated various code comments throughout > > > > --- > > > > Alexander Duyck (5): > > mm: Adjust shuffle code to allow for future coalescing > > mm: Move set/get_pcppage_migratetype to mmzone.h > > mm: Use zone and order instead of free area in free_list manipulators > > mm: Introduce Hinted pages > > virtio-balloon: Add support for providing page hints to host > > > > > > drivers/virtio/Kconfig | 1 > > drivers/virtio/virtio_balloon.c | 47 ++++++ > > include/linux/mmzone.h | 116 ++++++++------ > > include/linux/page-flags.h | 8 + > > include/linux/page_hinting.h | 139 ++++++++++++++++ > > include/uapi/linux/virtio_balloon.h | 1 > > mm/Kconfig | 5 + > > mm/Makefile | 1 > > mm/internal.h | 18 ++ > > mm/memory_hotplug.c | 1 > > mm/page_alloc.c | 238 ++++++++++++++++++++-------- > > mm/page_hinting.c | 298 +++++++++++++++++++++++++++++++++++ > > mm/shuffle.c | 24 --- > > mm/shuffle.h | 32 ++++ > > 14 files changed, 796 insertions(+), 133 deletions(-) > > create mode 100644 include/linux/page_hinting.h > > create mode 100644 mm/page_hinting.c > > > > -- > -- > Thanks > Nitesh
