lkml.org 
[lkml]   [2019]   [Apr]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v6 03/12] mm/sparsemem: Add helpers track active portions of a section at boot
On Wed, Apr 17, 2019 at 11:39:11AM -0700, Dan Williams wrote:
> Prepare for hot{plug,remove} of sub-ranges of a section by tracking a
> section active bitmask, each bit representing 2MB (SECTION_SIZE (128M) /
> map_active bitmask length (64)). If it turns out that 2MB is too large
> of an active tracking granularity it is trivial to increase the size of
> the map_active bitmap.
>
> The implications of a partially populated section is that pfn_valid()
> needs to go beyond a valid_section() check and read the sub-section
> active ranges from the bitmask.
>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: Logan Gunthorpe <logang@deltatee.com>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
[...]
> +static unsigned long section_active_mask(unsigned long pfn,
> + unsigned long nr_pages)
> +{
> + int idx_start, idx_size;
> + phys_addr_t start, size;
> +
> + if (!nr_pages)
> + return 0;
> +
> + start = PFN_PHYS(pfn);
> + size = PFN_PHYS(min(nr_pages, PAGES_PER_SECTION
> + - (pfn & ~PAGE_SECTION_MASK)));
> + size = ALIGN(size, SECTION_ACTIVE_SIZE);

I am probably missing something, and this is more a question than anything else, but:
is there a reason for shifting pfn and pages to get the size and the address?
Could not we operate on pfn/pages, so we do not have to shift every time?
(even for pfn_section_valid() calls)

Something like:

#define SUB_SECTION_ACTIVE_PAGES (SECTION_ACTIVE_SIZE / PAGE_SIZE)

static inline int section_active_index(unsigned long pfn)
{
return (pfn & ~(PAGE_SECTION_MASK)) / SUB_SECTION_ACTIVE_PAGES;
}

> +
> + idx_start = section_active_index(start);
> + idx_size = section_active_index(size);
> +
> + if (idx_size == 0)
> + return -1;

What about turning that into something more intuitive?
Since -1 represents here a full section, we could define something like:

#define FULL_SECTION (-1UL)

Or a better name, it is just that I find "-1" not really easy to interpret.

> + return ((1UL << idx_size) - 1) << idx_start;
> +}
> +
> +void section_active_init(unsigned long pfn, unsigned long nr_pages)
> +{
> + int end_sec = pfn_to_section_nr(pfn + nr_pages - 1);
> + int i, start_sec = pfn_to_section_nr(pfn);
> +
> + if (!nr_pages)
> + return;
> +
> + for (i = start_sec; i <= end_sec; i++) {
> + struct mem_section *ms;
> + unsigned long mask;
> + unsigned long pfns;
> +
> + pfns = min(nr_pages, PAGES_PER_SECTION
> + - (pfn & ~PAGE_SECTION_MASK));
> + mask = section_active_mask(pfn, pfns);
> +
> + ms = __nr_to_section(i);
> + pr_debug("%s: sec: %d mask: %#018lx\n", __func__, i, mask);
> + ms->usage->map_active = mask;
> +
> + pfn += pfns;
> + nr_pages -= pfns;
> + }
> +}
> +
> /* Record a memory area against a node. */
> void __init memory_present(int nid, unsigned long start, unsigned long end)
> {
>

--
Oscar Salvador
SUSE L3

\
 
 \ /
  Last update: 2019-04-26 14:58    [W:0.430 / U:0.900 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site