On 8/1/19 6:24 PM, Alexander Duyck wrote: > This series provides an asynchronous means of reporting 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 unused page reporting > > The functionality for this is fairly simple. When enabled it will allocate > statistics to track the number of reported pages in a given free area. > When the number of free pages exceeds this value plus a high water value, > currently 32, it will begin performing page reporting which consists of > pulling pages off of free list and placing them into a scatter list. The > scatterlist is then given to the page reporting device and it will perform > the required action to make the pages "reported", 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 reported buddy page instead of a > standard buddy page. The cycle then repeats with additional non-reported > pages being pulled until the free areas all consist of reported pages. > > I am leaving a number of things hard-coded such as limiting the lowest > order processed to PAGEBLOCK_ORDER, 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. The upper limit for this is based on the size of the > queue used to store the scatterlist. > > My primary testing has just been to verify the memory is being freed after > allocation by running memhog 40g on a 40g 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 up to a 2% difference between the base > kernel without these patches and the patches with virtio-balloon enabled > or disabled.
A couple of questions: - The 2% difference which you have mentioned, is this visible for all the 16 cores or just the 16th core? - I am assuming that the difference is seen for both "number of process" and "number of threads" launched by page_fault1. Is that right? > > One side effect of these patches is that the guest becomes much more > resilient in terms of NUMA locality. With the pages being freed and then > reallocated when used it allows for the pages to be much closer to the > active thread, and as a result there can be situations where this patch > set will out-perform the stock kernel when the guest memory is not local > to the guest vCPUs. Was this the reason because of which you were seeing better results for page_fault1 earlier? > > 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 that had not yet 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 boundary 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" > 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 intermediate array > Moved stats out of free_area, now in separate area and pointed to from zone > Merged patch 5 into patch 4 to improve review-ability > Updated various code comments throughout > > Changes from v2: > https://lore.kernel.org/lkml/20190724165158.6685.87228.stgit@localhost.localdomain/ > Dropped "page hinting" in favor of "page reporting" > Renamed files from "hinting" to "reporting" > Replaced "Hinted" page type with "Reported" page flag > Added support for page poisoning while hinting is active > Add QEMU patch that implements PAGE_POISON feature > > --- > > Alexander Duyck (6): > 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 Reported pages > virtio-balloon: Pull page poisoning config out of free page hinting > virtio-balloon: Add support for providing unused page reports to host > > > drivers/virtio/Kconfig | 1 > drivers/virtio/virtio_balloon.c | 75 ++++++++- > include/linux/mmzone.h | 116 ++++++++------ > include/linux/page-flags.h | 11 + > include/linux/page_reporting.h | 138 ++++++++++++++++ > 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_reporting.c | 299 > +++++++++++++++++++++++++++++++++++ > mm/shuffle.c | 24 --- > mm/shuffle.h | 32 ++++ > 14 files changed, 821 insertions(+), 139 deletions(-) > create mode 100644 include/linux/page_reporting.h > create mode 100644 mm/page_reporting.c > > -- > -- Thanks Nitesh
