lkml.org 
[lkml]   [2019]   [Sep]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    SubjectRe: [RFC PATCH v2] mm: initialize struct pages reserved by ZONE_DEVICE driver.
    Date
    On 2019/09/18 2:04, Waiman Long wrote:
    > On 9/17/19 12:21 PM, Qian Cai wrote:
    >> On Tue, 2019-09-17 at 11:49 -0400, Waiman Long wrote:
    >>> On 9/17/19 3:13 AM, David Hildenbrand wrote:
    >>>> On 17.09.19 04:34, Toshiki Fukasawa wrote:
    >>>>> On 2019/09/09 16:46, David Hildenbrand wrote:
    >>>>>> Let's take a step back here to understand the issues I am aware of. I
    >>>>>> think we should solve this for good now:
    >>>>>>
    >>>>>> A PFN walker takes a look at a random PFN at a random point in time. It
    >>>>>> finds a PFN with SECTION_MARKED_PRESENT && !SECTION_IS_ONLINE. The
    >>>>>> options are:
    >>>>>>
    >>>>>> 1. It is buddy memory (add_memory()) that has not been online yet. The
    >>>>>> memmap contains garbage. Don't access.
    >>>>>>
    >>>>>> 2. It is ZONE_DEVICE memory with a valid memmap. Access it.
    >>>>>>
    >>>>>> 3. It is ZONE_DEVICE memory with an invalid memmap, because the section
    >>>>>> is only partially present: E.g., device starts at offset 64MB within a
    >>>>>> section or the device ends at offset 64MB within a section. Don't access it.
    >>>>> I don't agree with case #3. In the case, struct page area is not allocated on
    >>>>> ZONE_DEVICE, but is allocated on system memory. So I think we can access the
    >>>>> struct pages. What do you mean "invalid memmap"?
    >>>> No, that's not the case. There is no memory, especially not system
    >>>> memory. We only allow partially present sections (sub-section memory
    >>>> hotplug) for ZONE_DEVICE.
    >>>>
    >>>> invalid memmap == memmap was not initialized == struct pages contains
    >>>> garbage. There is a memmap, but accessing it (e.g., pfn_to_nid()) will
    >>>> trigger a BUG.
    >>>>
    >>> As long as the page structures exist, they should be initialized to some
    >>> known state. We could set PagePoison for those invalid memmap. It is the
    >> Sounds like you want to run page_init_poison() by default.
    >
    > Yes for those pages that are not initialized otherwise. I don't want to
    > run page_init_poison() for the whole ZONE_DEVICE memory range as it can
    > take a while if we are talking about TBs of persistent memory. Also most
    > of the pages will be reinitialized anyway in the init process. So it is
    > mostly a wasted effort. However, for those reserved pages that are not
    > being exported to the memory management layer, having them initialized
    > to a known state will cause less problem down the road.
    >
    The same can be said about altmap->reserve. I think it should be initialized
    since the struct page exists.

    Thanks,
    Toshiki Fukasawa

    \
     
     \ /
      Last update: 2019-09-18 04:45    [W:3.820 / U:0.580 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site