Messages in this thread | | | Date | Mon, 15 Feb 2021 23:24:40 +0200 | From | Mike Rapoport <> | Subject | Re: [PATCH v5 1/1] mm: refactor initialization of struct page for holes in memory layout |
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On Mon, Feb 15, 2021 at 10:00:31AM +0100, Michal Hocko wrote: > On Sun 14-02-21 20:00:16, Mike Rapoport wrote: > > On Fri, Feb 12, 2021 at 02:18:20PM +0100, Michal Hocko wrote: > > > We can correctly set the zone links for the reserved pages for holes in the > > middle of a zone based on the architecture constraints and with only the > > holes in the beginning/end of the memory will be not spanned by any > > node/zone which in practice does not seem to be a problem as the VM_BUG_ON > > in set_pfnblock_flags_mask() never triggered on pfn 0. > > I really fail to see what you mean by correct zone/node for a memory > range which is not associated with any real node.
We know architectural zone constraints, so we can have always have 1:1 match from pfn to zone. Node indeed will be a guess.
> > > I am sorry, I haven't followed previous discussions. Has the removal of > > > the VM_BUG_ON been considered as an immediate workaround? > > > > It was never discussed, but I'm not sure it's a good idea. > > > > Judging by the commit message that introduced the VM_BUG_ON (commit > > 86051ca5eaf5 ("mm: fix usemap initialization")) there was yet another > > inconsistency in the memory map that required a special care. > > Can we actually explore that path before adding yet additional > complexity and potentially a very involved fix for a subtle problem?
This patch was intended as a fix for inconsistency of the memory map that is the root cause for triggering this VM_BUG_ON and other corner case problems.
The previous version [1] is less involved as it does not extend node/zone spans.
[1] https://lore.kernel.org/lkml/20210130221035.4169-3-rppt@kernel.org -- Sincerely yours, Mike.
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