From: Gavin Shan <gshan@xxxxxxxxxx> Sent: Monday, June 21, 2021 7:05 PM > > On 6/22/21 2:06 AM, Michael Kelley wrote: > > From: Alexander Duyck <alexander.duyck@xxxxxxxxx> Sent: Monday, June 21, 2021 7:02 > AM > >> To: Gavin Shan <gshan@xxxxxxxxxx> > >> Cc: linux-mm <linux-mm@xxxxxxxxx>; LKML <linux-kernel@xxxxxxxxxxxxxxx>; Andrew > >> Morton <akpm@xxxxxxxxxxxxxxxxxxxx>; David Hildenbrand <david@xxxxxxxxxx>; > >> Anshuman Khandual <anshuman.khandual@xxxxxxx>; Catalin Marinas > >> <catalin.marinas@xxxxxxx>; Will Deacon <will@xxxxxxxxxx>; shan.gavin@xxxxxxxxx > >> Subject: Re: [PATCH 0/3] mm/page_reporting: Make page reporting work on arm64 with > >> 64KB page size > >> > >> So the question I would have is what is the use case for this? It > >> seems like you don't have to deal with the guest native page size > >> issues since you are willing to break up what would otherwise be THP > >> pages on the guest, and the fact that you are willing to go down to > >> 2MB pages which happens to align with the host THP page size for x86 > >> makes me wonder if that is actually the environment you are running > >> in. > >> > >> Rather than having the guest control this it might make sense to look > >> at adding an interface so that the page_reporting_register function > >> and the page_reporting_dev_info struct could be used to report and > >> configure the minimum page size that the host can support for the page > >> reporting. With that the host could then guarantee that it isn't going > >> to hurt performance by splitting pages on the host and risk hurting > >> the virtualization performance. > >> > >> Also you would benefit by looking into the callers of > >> page_reporting_register as there are more than just the virtio balloon > >> that are consuming it. Odds are HyperV won't care about an ARM64 > >> architecture, > > > > FWIW, Hyper-V *does* care about ARM64. It's already in use by > > the Windows Subsystem for Linux VM that's part of Windows 10 > > on ARM64 hardware. We're working to get the code accepted > > upstream. > > > > Michael, thanks for your confirmation. As the issue found on 64KB guest > when memory balloon is used, lets resolve the case first. I will look > into Hyper-V case later if you agree. It won't be difficult to fix the > same issue for Hyper-V after the solution is figured out for memory > balloon. > > Thanks, > Gavin This should be fine. For reference, the Hyper-V ARM64 host always runs with a base page size of 4K. Linux guests on Hyper-V may have base page size of 4K, 16K, or 64K. Michael > > > > >> but your change would essentially disable it outright > >> which is why I think this might be better to address via the consumers > >> of page reporting rather than trying to address it in page reporting > >> itself. > >> > >> Thanks, > >> > >> - Alex > >> > >> On Sun, Jun 20, 2021 at 8:11 PM Gavin Shan <gshan@xxxxxxxxxx> wrote: > >>> > >>> The page reporting threshold is currently equal to @pageblock_order, which > >>> is 13 and 512MB on arm64 with 64KB base page size selected. The page > >>> reporting won't be triggered if the freeing page can't come up with a free > >>> area like that huge. The condition is hard to be met, especially when the > >>> system memory becomes fragmented. > >>> > >>> This series intends to solve the issue by having page reporting threshold > >>> as 5 (2MB) on arm64 with 64KB base page size. The patches are organized as: > >>> > >>> PATCH[1/3] introduces variable (@page_reporting_order) to replace original > >>> macro (PAGE_REPORTING_MIN_ORDER). It's also exported so that it > >>> can be adjusted at runtime. > >>> PATCH[2/3] renames PAGE_REPORTING_MIN_ORDER with > PAGE_REPORTING_ORDER > >> and > >>> allows architecture to specify its own version. > >>> PATCH[3/3] defines PAGE_REPORTING_ORDER to 5, corresponding to 2MB in size, > >>> on arm64 when 64KB base page size is selected. It's still same > >>> as to @pageblock_order for other architectures and cases. > >>> > >>> Gavin Shan (3): > >>> mm/page_reporting: Allow to set reporting order > >>> mm/page_reporting: Allow architecture to select reporting order > >>> arm64: mm: Specify smaller page reporting order > >>> > >>> Documentation/admin-guide/kernel-parameters.txt | 6 ++++++ > >>> arch/arm64/include/asm/page.h | 13 +++++++++++++ > >>> mm/page_reporting.c | 8 ++++++-- > >>> mm/page_reporting.h | 10 +++++++--- > >>> 4 files changed, 32 insertions(+), 5 deletions(-) > >>> > >>> -- > >>> 2.23.0 > >>>
