Messages in this thread | | | From | Jérôme Glisse <> | Subject | [PATCH] x86/mm: pgds getting out of sync after memory hot remove | Date | Fri, 19 May 2017 14:01:26 -0400 |
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After memory hot remove it seems we do not synchronize pgds for kernel virtual memory range (on vmemmap_free()). This seems bogus to me as it means we are left with stall entry for process with mm != mm_init
Yet i am puzzle by the fact that i am only now hitting this issue. It never was an issue with 4.12 or before ie HMM never triggered following BUG_ON inside sync_global_pgds():
if (!p4d_none(*p4d_ref) && !p4d_none(*p4d)) BUG_ON(p4d_page_vaddr(*p4d) != p4d_page_vaddr(*p4d_ref));
It seems that Kirill 5 level page table changes play a role in this behavior change. I could not bisect because HMM is painfull to rebase for each bisection step so that is just my best guess.
Am i missing something here ? Am i wrong in assuming that should sync pgd on vmemmap_free() ? If so anyone have a good guess on why i am now seeing the above BUG_ON ?
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Ingo Molnar <mingo@kernel.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Mel Gorman <mgorman@suse.de>
Jérôme Glisse (1): x86/mm: synchronize pgd in vmemmap_free()
arch/x86/mm/init_64.c | 17 ++++++++++------- 1 file changed, 10 insertions(+), 7 deletions(-)
-- 2.4.11
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