On Tue, Jul 24, 2018 at 9:31 PM Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > > On Tue, 24 Jul 2018 19:55:19 -0400 Pavel Tatashin <pasha.tatashin@xxxxxxxxxx> wrote: > > > update_defer_init() should be called only when struct page is about to be > > initialized. Because it counts number of initialized struct pages, but > > there we may skip struct pages if there is some mirrored memory. > > > > So move, update_defer_init() after checking for mirrored memory. > > > > Also, rename update_defer_init() to defer_init() and reverse the return > > boolean to emphasize that this is a boolean function, that tells that the > > reset of memmap initialization should be deferred. > > > > Make this function self-contained: do not pass number of already > > initialized pages in this zone by using static counters. > > > > ... > > > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -306,24 +306,28 @@ static inline bool __meminit early_page_uninitialised(unsigned long pfn) > > } > > > > /* > > - * Returns false when the remaining initialisation should be deferred until > > + * Returns true when the remaining initialisation should be deferred until > > * later in the boot cycle when it can be parallelised. > > */ > > -static inline bool update_defer_init(pg_data_t *pgdat, > > - unsigned long pfn, unsigned long zone_end, > > - unsigned long *nr_initialised) > > +static inline bool defer_init(int nid, unsigned long pfn, unsigned long end_pfn) > > { > > + static unsigned long prev_end_pfn, nr_initialised; > > So answer me quick, what happens with a static variable in an inlined > function? Is there one copy kernel-wide? One copy per invocation > site? One copy per compilation unit? > > Well I didn't know so I wrote a little test. One copy per compilation > unit (.o file), it appears. > > It's OK in this case because the function is in .c (and has only one > call site). But if someone moves it into a header and uses it from a > different .c file, they have problems. > > So it's dangerous, and poor practice. I'll make this non-static > __meminit. I agree, it should not be moved to header it is dangerous. But, on the other hand this is a hot-path. memmap_init_zone() might need to go through billions of struct pages early in boot, and I did not want us to waste time on function calls. With defer_init() this is not a problem, because if CONFIG_DEFERRED_STRUCT_PAGE_INIT is set memmap_init_zone() won't have much work to do, but for overlap_memmap_init() this is a problem, especially because I expect compiler to optimize the pfn dereference usage in inline function. > > --- a/mm/page_alloc.c~mm-calculate-deferred-pages-after-skipping-mirrored-memory-fix > +++ a/mm/page_alloc.c > @@ -309,7 +309,8 @@ static inline bool __meminit early_page_ > * Returns true when the remaining initialisation should be deferred until > * later in the boot cycle when it can be parallelised. > */ > -static inline bool defer_init(int nid, unsigned long pfn, unsigned long end_pfn) > +static bool __meminit > +defer_init(int nid, unsigned long pfn, unsigned long end_pfn) > { > static unsigned long prev_end_pfn, nr_initialised; > > > Also, what locking protects these statics? Our knowledge that this > code is single-threaded, presumably? Correct, this is called only from "context == MEMMAP_EARLY", way before smp_init().