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SubjectRe: [-mm PATCH] register_memory/unregister_memory clean ups
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On Tue, 2008-02-12 at 09:22 -0800, Badari Pulavarty wrote:
> +static void __remove_section(struct zone *zone, unsigned long phys_start_pfn)
> +{
> + if (!pfn_valid(phys_start_pfn))
> + return;

I think you need at least a WARN_ON() there.

I'd probably also not use pfn_valid(), personally.

> + unregister_memory_section(__pfn_to_section(phys_start_pfn));
> + __remove_zone(zone, phys_start_pfn);
> + sparse_remove_one_section(zone, phys_start_pfn, PAGES_PER_SECTION);
> +}

Can none of this ever fail?

I also think having a function called __remove_section() that takes a
pfn is a bad idea. How about passing an actual 'struct mem_section *'
into it? One of the reasons I even made that structure was so that you
could hand it around to things and never be confused about pfn vs. paddr
vs. vaddr vs. section_nr. Please use it.

> /*
> * Reasonably generic function for adding memory. It is
> * expected that archs that support memory hotplug will
> @@ -135,6 +153,21 @@ int __add_pages(struct zone *zone, unsig
> }
> EXPORT_SYMBOL_GPL(__add_pages);
>
> +void __remove_pages(struct zone *zone, unsigned long phys_start_pfn,
> + unsigned long nr_pages)
> +{
> + unsigned long i;
> + int start_sec, end_sec;
> +
> + start_sec = pfn_to_section_nr(phys_start_pfn);
> + end_sec = pfn_to_section_nr(phys_start_pfn + nr_pages - 1);
> +
> + for (i = start_sec; i <= end_sec; i++)
> + __remove_section(zone, i << PFN_SECTION_SHIFT);
> +
> +}
> +EXPORT_SYMBOL_GPL(__remove_pages);

I'd like to see some warnings in there if nr_pages or phys_start_pfn are
not section-aligned and some other sanity checks. If someone is trying
to remove non-section-aligned areas, we either have something wrong, or
some other work to do, first keeping track of what section portions are
"removed".

I'd probably do:

void __remove_pages(struct zone *zone, unsigned long phys_start_pfn,
unsigned long nr_pages)
{
int i;
int sections_to_remove;
/*
* We can only remove entire sections.
*/
if (phys_start_pfn & ~PAGE_SECTION_MASK)
return ...;
if (nr_pages % PAGES_PER_SECTION)
return ...;
sections_to_remove = nr_pages / PAGES_PER_SECTION;
for (i = 0; i < sections_to_remove; i++) {
unsigned long pfn = phys_start_pfn + i*PAGES_PER_SECTION;
__remove_section(zone, __pfn_to_section(pfn));
}
}

> static void grow_zone_span(struct zone *zone,
> unsigned long start_pfn, unsigned long end_pfn)
> {
> Index: linux-2.6.24/mm/sparse.c
> ===================================================================
> --- linux-2.6.24.orig/mm/sparse.c 2008-02-07 17:16:52.000000000 -0800
> +++ linux-2.6.24/mm/sparse.c 2008-02-11 14:12:28.000000000 -0800
> @@ -415,4 +415,44 @@ out:
> }
> return ret;
> }
> +
> +void sparse_remove_one_section(struct zone *zone, unsigned long start_pfn,
> + int nr_pages)
> +{
> + unsigned long section_nr = pfn_to_section_nr(start_pfn);
> + struct pglist_data *pgdat = zone->zone_pgdat;
> + struct mem_section *ms;
> + struct page *memmap = NULL;
> + unsigned long *usemap = NULL;
> + unsigned long flags;
> +
> + pgdat_resize_lock(pgdat, &flags);
> + ms = __pfn_to_section(start_pfn);
> + if (ms->section_mem_map) {
> + memmap = ms->section_mem_map & SECTION_MAP_MASK;

You're abusing this memmap variable. Please make another variable
that's unsigned long and has a nice name if you're actually going to
store an 'unsigned long' in it. That cast below should be a big red
flag.

> + usemap = ms->pageblock_flags;
> + memmap = sparse_decode_mem_map((unsigned long)memmap,
> + section_nr);
> + ms->section_mem_map = 0;
> + ms->pageblock_flags = NULL;
> + }
> + pgdat_resize_unlock(pgdat, &flags);

Ugh. Please put this in its own helper. Also, sparse_decode_mem_map()
has absolutely no other users. Please modify it so that you don't have
to do this gunk, like put the '& SECTION_MAP_MASK' in there. You
probably just need:

struct page *sparse_decode_mem_map(unsigned long coded_mem_map, unsigned long pnum)
{
/*
* mask off the extra low bits of information
*/
coded_mem_map &= SECTION_MAP_MASK;
return ((struct page *)coded_mem_map) + section_nr_to_pfn(pnum);
}
Then, you can just do this:

memmap = sparse_decode_mem_map(ms->section_mem_map, section_nr);

No casting, no temp variables. *PLEASE* look around at things and feel
free to modify to modify them. Otherwise, it'll just become a mess.
(oh, and get rid of the unused attribute on it).

> +
> + /*
> + * Its ugly, but this is the best I can do - HELP !!
> + * We don't know where the allocations for section memmap and usemap
> + * came from. If they are allocated at the boot time, they would come
> + * from bootmem. If they are added through hot-memory-add they could be
> + * from sla or vmalloc. If they are allocated as part of hot-mem-add
> + * free them up properly. If they are allocated at boot, no easy way
> + * to correctly free them :(
> + */
> + if (usemap) {
> + if (PageSlab(virt_to_page(usemap))) {
> + kfree(usemap);
> + if (memmap)
> + __kfree_section_memmap(memmap, nr_pages);
> + }
> + }
> +}

Do what we did with the memmap and store some of its origination
information in the low bits.

-- Dave



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