Messages in this thread | | | Date | Wed, 10 Oct 2018 20:52:12 +0800 | From | Yi Zhang <> | Subject | Re: [PATCH v5 4/4] mm: Defer ZONE_DEVICE page initialization to the point where we init pgmap |
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On 2018-10-09 at 14:19:32 -0700, Dan Williams wrote: > On Tue, Oct 9, 2018 at 1:34 PM Alexander Duyck > <alexander.h.duyck@linux.intel.com> wrote: > > > > On 10/9/2018 11:04 AM, Dan Williams wrote: > > > On Tue, Oct 9, 2018 at 3:21 AM Yi Zhang <yi.z.zhang@linux.intel.com> wrote: > [..] > > > That comment is incorrect, device-pages are never onlined. So I think > > > we can just skip that call to __SetPageReserved() unless the memory > > > range is MEMORY_DEVICE_{PRIVATE,PUBLIC}. > > > > > > > When pages are "onlined" via __free_pages_boot_core they clear the > > reserved bit, that is the reason for the comment. The reserved bit is > > meant to indicate that the page cannot be swapped out or moved based on > > the description of the bit. > > ...but ZONE_DEVICE pages are never onlined so I would expect > memmap_init_zone_device() to know that detail. > > > I would think with that being the case we still probably need the call > > to __SetPageReserved to set the bit with the expectation that it will > > not be cleared for device-pages since the pages are not onlined. > > Removing the call to __SetPageReserved would probably introduce a number > > of regressions as there are multiple spots that use the reserved bit to > > determine if a page can be swapped out to disk, mapped as system memory, > > or migrated.
Another things, it seems page_init/set_reserved already been done in the move_pfn_range_to_zone |-->memmap_init_zone |-->for_each_page_in_pfn |-->__init_single_page |-->SetPageReserved
Why we haven't remove these redundant initial in memmap_init_zone?
Correct me if I missed something.
> > Right, this is what Yi is working on... the PageReserved flag is > problematic for KVM. Auditing those locations it seems as long as we > teach hibernation to avoid ZONE_DEVICE ranges we can safely not set > the reserved flag for DAX pages. What I'm trying to avoid is a local > KVM hack to check for DAX pages when the Reserved flag is not > otherwise needed. Thanks Dan. Provide the patch link.
https://lore.kernel.org/lkml/cover.1536342881.git.yi.z.zhang@linux.intel.com
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