On Wed 09-05-18 15:17:13, Pavel Tatashin wrote: > It is unsafe to do virtual to physical translations before mm_init() is > called if struct page is needed in order to determine the memory section > number (see SECTION_IN_PAGE_FLAGS). This is because only in mm_init() we > initialize struct pages for all the allocated memory when deferred struct > pages are used. > > My recent fix exposed this problem, because it greatly reduced number of > pages that are initialized before mm_init(), but the problem existed even > before my fix, as Fengguang Wu found. > > Since FLATMEM is already disallowed for deferred struct pages, it makes > sense to allow deferred struct pages only on systems with > SPARSEMEM_VMEMMAP. This doesn't really explain why CONFIG_SPARSMEM or DISCONTIG has the problem. > The problems are discussed in these threads: > http://lkml.kernel.org/r/20180418135300.inazvpxjxowogyge@xxxxxxxxxxxxxxxxxxxxxx > http://lkml.kernel.org/r/20180419013128.iurzouiqxvcnpbvz@xxxxxxxxxxxxxxxxxxxxxx > http://lkml.kernel.org/r/20180426202619.2768-1-pasha.tatashin@xxxxxxxxxx Using references is good but there should be a highlevel summary in the chaneglog as well. > Fixes: 3a80a7fa7989 ("mm: meminit: initialise a subset of struct pages if CONFIG_DEFERRED_STRUCT_PAGE_INIT is set") > Signed-off-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx> > --- > mm/Kconfig | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/Kconfig b/mm/Kconfig > index d5004d82a1d6..1cd32d67ca30 100644 > --- a/mm/Kconfig > +++ b/mm/Kconfig > @@ -635,7 +635,7 @@ config DEFERRED_STRUCT_PAGE_INIT > bool "Defer initialisation of struct pages to kthreads" > default n > depends on NO_BOOTMEM > - depends on !FLATMEM > + depends on SPARSEMEM_VMEMMAP > help > Ordinarily all struct pages are initialised during early boot in a > single thread. On very large machines this can take a considerable > -- > 2.17.0 > -- Michal Hocko SUSE Labs
