On Mon, 2015-01-26 at 15:54 -0800, Andrew Morton wrote:
> On Mon, 26 Jan 2015 16:13:24 -0700 Toshi Kani <toshi.kani@xxxxxx> wrote:
>
> > Add ioremap_pud_enabled() and ioremap_pmd_enabled(), which
> > return 1 when I/O mappings of pud/pmd are enabled on the kernel.
> >
> > ioremap_huge_init() calls arch_ioremap_pud_supported() and
> > arch_ioremap_pmd_supported() to initialize the capabilities.
> >
> > A new kernel option "nohgiomap" is also added, so that user can
> > disable the huge I/O map capabilities if necessary.
>
> Why? What's the problem with leaving it enabled?
No, there should not be any problem with leaving it enabled. This
option is added as a way to workaround a problem when someone hit an
issue unexpectedly.
> > --- a/Documentation/kernel-parameters.txt
> > +++ b/Documentation/kernel-parameters.txt
> > @@ -2304,6 +2304,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
> > register save and restore. The kernel will only save
> > legacy floating-point registers on task switch.
> >
> > + nohgiomap [KNL,x86] Disable huge I/O mappings.
>
> That reads like "no high iomap" to me. "nohugeiomap" would be better.
Agreed. Will use "nohugeiomap".
> > --- a/lib/ioremap.c
> > +++ b/lib/ioremap.c
> > @@ -13,6 +13,44 @@
> > #include <asm/cacheflush.h>
> > #include <asm/pgtable.h>
> >
> > +#ifdef CONFIG_HUGE_IOMAP
> > +int __read_mostly ioremap_pud_capable;
> > +int __read_mostly ioremap_pmd_capable;
> > +int __read_mostly ioremap_huge_disabled;
> > +
> > +static int __init set_nohgiomap(char *str)
> > +{
> > + ioremap_huge_disabled = 1;
> > + return 0;
> > +}
> > +early_param("nohgiomap", set_nohgiomap);
>
> Why early?
On my system, the first ioremap() call is made at:
start_kernel()
-> late_time_init()
-> x86_late_time_init()
-> hpet_time_init()
I think this is too early for module_param(). Also, lib/ioremap.c is
not really a module.
> > +static inline void ioremap_huge_init(void)
> > +{
> > + if (!ioremap_huge_disabled) {
> > + if (arch_ioremap_pud_supported())
> > + ioremap_pud_capable = 1;
> > + if (arch_ioremap_pmd_supported())
> > + ioremap_pmd_capable = 1;
> > + }
> > +}
> > +
> > +static inline int ioremap_pud_enabled(void)
> > +{
> > + return ioremap_pud_capable;
> > +}
> > +
> > +static inline int ioremap_pmd_enabled(void)
> > +{
> > + return ioremap_pmd_capable;
> > +}
> > +
> > +#else /* !CONFIG_HUGE_IOMAP */
> > +static inline void ioremap_huge_init(void) { }
> > +static inline int ioremap_pud_enabled(void) { return 0; }
> > +static inline int ioremap_pmd_enabled(void) { return 0; }
> > +#endif /* CONFIG_HUGE_IOMAP */
> > +
> > static int ioremap_pte_range(pmd_t *pmd, unsigned long addr,
> > unsigned long end, phys_addr_t phys_addr, pgprot_t prot)
> > {
> > @@ -74,6 +112,12 @@ int ioremap_page_range(unsigned long addr,
> > unsigned long start;
> > unsigned long next;
> > int err;
> > + static int ioremap_huge_init_done;
> > +
> > + if (!ioremap_huge_init_done) {
> > + ioremap_huge_init_done = 1;
> > + ioremap_huge_init();
> > + }
>
> Looks hacky. Why can't we just get the startup ordering correct? It
> at least needs a comment which fully explains the situation.
How about calling it from mm_init() after vmalloc_init()?
void __init mm_init(void)
:
percpu_init_late();
pgtable_init();
vmalloc_init();
+ ioremap_huge_init();
}
Thanks,
-Toshi
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>