On Wed 12-08-20 20:51:38, Doug Berger wrote: > The lowmem_reserve arrays provide a means of applying pressure > against allocations from lower zones that were targeted at > higher zones. Its values are a function of the number of pages > managed by higher zones and are assigned by a call to the > setup_per_zone_lowmem_reserve() function. > > The function is initially called at boot time by the function > init_per_zone_wmark_min() and may be called later by accesses > of the /proc/sys/vm/lowmem_reserve_ratio sysctl file. > > The function init_per_zone_wmark_min() was moved up from a > module_init to a core_initcall to resolve a sequencing issue > with khugepaged. Unfortunately this created a sequencing issue > with CMA page accounting. > > The CMA pages are added to the managed page count of a zone > when cma_init_reserved_areas() is called at boot also as a > core_initcall. This makes it uncertain whether the CMA pages > will be added to the managed page counts of their zones before > or after the call to init_per_zone_wmark_min() as it becomes > dependent on link order. With the current link order the pages > are added to the managed count after the lowmem_reserve arrays > are initialized at boot. > > This means the lowmem_reserve values at boot may be lower than > the values used later if /proc/sys/vm/lowmem_reserve_ratio is > accessed even if the ratio values are unchanged. > > In many cases the difference is not significant, but in others > it may have an affect.
Could you be more specific please? > This commit breaks the link order dependency by invoking > init_per_zone_wmark_min() as a postcore_initcall so that the > CMA pages have the chance to be properly accounted in their > zone(s) and allowing the lowmem_reserve arrays to receive > consistent values. > > Fixes: bc22af74f271 ("mm: update min_free_kbytes from khugepaged after core > initialization") > Signed-off-by: Doug Berger <open...@gmail.com> > --- > mm/page_alloc.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 8b7d0ecf30b1..f3e340ec2b6b 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -7887,7 +7887,7 @@ int __meminit init_per_zone_wmark_min(void) > > return 0; > } > -core_initcall(init_per_zone_wmark_min) > +postcore_initcall(init_per_zone_wmark_min) > > /* > * min_free_kbytes_sysctl_handler - just a wrapper around proc_dointvec() so > -- > 2.7.4 > -- Michal Hocko SUSE Labs