Re: [PATCH 2/2] Add mem_type in /syfs to show memblock migrate type

[Badari Pulavarty <pbadari@us.ibm.com>]

On Thu, 2007-10-25 at 09:52 -0700, Dave Hansen wrote:
> On Thu, 2007-10-25 at 08:55 -0700, Badari Pulavarty wrote:
> > 
> > +static ssize_t show_mem_type(struct sys_device *dev, char *buf)
> > +{
> > +       struct page *page;
> > +       int type;
> > +       int i = pageblock_nr_pages;
> > +       struct memory_block *mem =
> > +               container_of(dev, struct memory_block, sysdev);
> > +
> > +       /*
> > +        * Get the type of first page in the block
> > +        */
> > +       page = pfn_to_page(section_nr_to_pfn(mem->phys_index));
> > +       type = get_pageblock_migratetype(page);
> > +
> > +       /*
> > +        * Check the migrate type of other pages in this section.
> > +        * If the type doesn't match, report it.
> > +        */
> > +       while (i < PAGES_PER_SECTION) {
> > +               if (type != get_pageblock_migratetype(page + i))
> > +                       return sprintf(buf, "Multiple\n");
> > +               i += pageblock_nr_pages;
> > +       } 
> 
> I might change this to be a bit more generic.  The odds are that the
> existence of a "pageblock" or the types of "pageblocks" will either
> change or go away over time.
> 
> But, a simple boolean "yes you have a good shot of removing this memory"
> or "you have a snowball's chance in hell" on removability is likely
> generic enough to stand the test of time.
> 
> That is, after all, what you're after here, right?
> 
> So, I'd rewrite that loop to look for the removable pageblock types and
> see if the entire section is make up of removable pageblocks, or if it
> has some party crashing non-removable pageblocks in ther.


I agree with you that all I care about are the "movable" sections 
for remove. But what we are doing here is, exporting the migrate type
to user-space and let the user space make a decision on what type
of sections to use for its use. For now, we can migrate/remove ONLY
"movable" sections. But in the future, we may be able to migrate/remove
"Reclaimable" ones. I don't know.

I don't want to make decisions in the kernel for removability - as
it might change depending on the situation. All I want is to export
the info and let user-space deal with the decision making.

Thanks,
Badari

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