Re: [RFC][PATCH] vmalloc: simplify vread()/vwrite()

From: Wu Fengguang
Date: Thu Jan 07 2010 - 00:31:11 EST


On Thu, Jan 07, 2010 at 11:23:04AM +0800, KAMEZAWA Hiroyuki wrote:
> On Thu, 07 Jan 2010 11:15:41 +0800
> Huang Ying <ying.huang@xxxxxxxxx> wrote:
>
> > > >
> > > > > The page_is_ram() check is necessary because kmap_atomic() is not
> > > > > designed to work with non-RAM pages.
> > > > >
> > > > I think page_is_ram() is not a complete method...on x86, it just check
> > > > e820's memory range. checking VM_IOREMAP is better, I think.
> > >
> > > (double check) Not complete or not safe?
> > >
> > > EFI seems to not update e820 table by default. Ying, do you know why?
> >
> > In EFI system, E820 table is constructed from EFI memory map in boot
> > loader, so I think you can rely on E820 table.
> >
> Yes, we can rely on. But concerns here is that we cannot get any
> information of ioremap via e820 map.
>
> But yes,
> == ioremap()
> 140 for (pfn = phys_addr >> PAGE_SHIFT;
> 141 (pfn << PAGE_SHIFT) < (last_addr & PAGE_MASK);
> 142 pfn++) {
> 143
> 144 int is_ram = page_is_ram(pfn);
> 145
> 146 if (is_ram && pfn_valid(pfn) && !PageReserved(pfn_to_page(pfn)))
> 147 return NULL;
> 148 WARN_ON_ONCE(is_ram);
> 149 }
> ==
> you'll get warned before access if "ram" area is remapped...

Right.

> But, about this patch, it seems that page_is_ram() is not free from architecture
> dependecy.

Yes this is a problem. We can provide a generic page_is_ram() as below.
And could further convert the existing x86 (and others) page_is_ram()
to be resource-based -- since at least for now the e820 table won't be
updated on memory hotplug.

Thanks,
Fengguang
---
include/linux/ioport.h | 2 ++
kernel/resource.c | 18 ++++++++++++++++++
2 files changed, 20 insertions(+)

--- linux-mm.orig/kernel/resource.c 2010-01-07 12:40:55.000000000 +0800
+++ linux-mm/kernel/resource.c 2010-01-07 13:13:46.000000000 +0800
@@ -297,6 +297,24 @@ int walk_system_ram_range(unsigned long

#endif

+static int __page_is_ram(unsigned long pfn, unsigned long nr_pages, void *arg)
+{
+ int *is_ram = arg;
+
+ *is_ram = 1;
+
+ return 1;
+}
+
+int __attribute__((weak)) page_is_ram(unsigned long pagenr)
+{
+ int is_ram = 0;
+
+ walk_system_ram_range(pagenr, 1, &is_ram, __page_is_ram);
+
+ return is_ram;
+}
+
/*
* Find empty slot in the resource tree given range and alignment.
*/
--- linux-mm.orig/include/linux/ioport.h 2010-01-07 13:11:43.000000000 +0800
+++ linux-mm/include/linux/ioport.h 2010-01-07 13:12:37.000000000 +0800
@@ -188,5 +188,7 @@ extern int
walk_system_ram_range(unsigned long start_pfn, unsigned long nr_pages,
void *arg, int (*func)(unsigned long, unsigned long, void *));

+extern int page_is_ram(unsigned long pagenr);
+
#endif /* __ASSEMBLY__ */
#endif /* _LINUX_IOPORT_H */
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/