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SubjectRe: [-mm PATCH] register_memory/unregister_memory clean ups
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On Tue, 2008-02-12 at 12:59 -0800, Dave Hansen wrote:
> 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.

Yes. I got similar feedback from Andy. I was closely trying to mimic
__add_pages() for easy review/understanding.

I have an updated version (not fully tested) which takes section_nr as
argument instead of playing with pfns. Please review this one and see if
it matches your taste :)

>
> > /*
> > * 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".
>

Yes. I did most of this already (thanks for pointing out again).


> > +void sparse_remove_one_section(struct zone *zone, unsigned long start_pfn,
> > + int nr_pages)
..
>
> > + 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).

Good suggestion.

>
> > +
> > + /*
> > + * 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.

Hmm. my understand of memmap is limited. Can you help me out here ?
I was trying to use free_bootmem_node() to free up the allocations,
but I need nodeid from which allocation came from :(

Here is the updated (currently testing) patch.

Thanks,
Badari

Generic helper function to remove section mappings and sysfs entries
for the section of the memory we are removing. offline_pages() correctly
adjusted zone and marked the pages reserved.

Issue: If mem_map, usemap allocation could come from different places -
kmalloc, vmalloc, alloc_pages or bootmem. There is no easy way
to find and free up properly. Especially for bootmem, we need to
know which node the allocation came from.

---
include/linux/memory_hotplug.h | 4 +++
mm/memory_hotplug.c | 30 ++++++++++++++++++++++++++++
mm/sparse.c | 43 ++++++++++++++++++++++++++++++++++++++---
3 files changed, 74 insertions(+), 3 deletions(-)
Index: linux-2.6.24/mm/memory_hotplug.c
===================================================================
--- linux-2.6.24.orig/mm/memory_hotplug.c 2008-02-07 17:16:52.000000000 -0800
+++ linux-2.6.24/mm/memory_hotplug.c 2008-02-12 13:35:52.000000000 -0800
@@ -102,6 +102,15 @@ static int __add_section(struct zone *zo
return register_new_memory(__pfn_to_section(phys_start_pfn));
}

+static void __remove_section(struct zone *zone, unsigned long section_nr)
+{
+ if (!valid_section_nr(section_nr))
+ return;
+
+ unregister_memory_section(__nr_to_section(section_nr));
+ sparse_remove_one_section(zone, section_nr);
+}
+
/*
* Reasonably generic function for adding memory. It is
* expected that archs that support memory hotplug will
@@ -135,6 +144,27 @@ 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 sections_to_remove;
+
+ /*
+ * We can only remove entire sections
+ */
+ BUG_ON(phys_start_pfn & ~PAGE_SECTION_MASK);
+ BUG_ON(nr_pages % PAGES_PER_SECTION);
+
+ 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_nr(pfn));
+ }
+}
+EXPORT_SYMBOL_GPL(__remove_pages);
+
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 2008-02-12 13:40:58.000000000 -0800
@@ -198,12 +198,13 @@ static unsigned long sparse_encode_mem_m
}

/*
- * We need this if we ever free the mem_maps. While not implemented yet,
- * this function is included for parity with its sibling.
+ * Decode mem_map from the coded memmap
*/
-static __attribute((unused))
+static
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);
}

@@ -415,4 +416,40 @@ out:
}
return ret;
}
+
+void sparse_remove_one_section(struct zone *zone, unsigned long section_nr)
+{
+ 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 = __nr_to_section(section_nr);
+ if (ms->section_mem_map) {
+ usemap = ms->pageblock_flags;
+ memmap = sparse_decode_mem_map(ms->section_mem_map, section_nr);
+ ms->section_mem_map = 0;
+ ms->pageblock_flags = NULL;
+ }
+ pgdat_resize_unlock(pgdat, &flags);
+
+ /*
+ * 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 slab, 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, PAGES_PER_SECTION);
+ }
+ }
+}
#endif
Index: linux-2.6.24/include/linux/memory_hotplug.h
===================================================================
--- linux-2.6.24.orig/include/linux/memory_hotplug.h 2008-02-07 17:16:52.000000000 -0800
+++ linux-2.6.24/include/linux/memory_hotplug.h 2008-02-12 13:37:47.000000000 -0800
@@ -64,6 +64,8 @@ extern int offline_pages(unsigned long,
/* reasonably generic interface to expand the physical pages in a zone */
extern int __add_pages(struct zone *zone, unsigned long start_pfn,
unsigned long nr_pages);
+extern void __remove_pages(struct zone *zone, unsigned long start_pfn,
+ unsigned long nr_pages);

/*
* Walk thorugh all memory which is registered as resource.
@@ -188,5 +190,7 @@ extern int arch_add_memory(int nid, u64
extern int remove_memory(u64 start, u64 size);
extern int sparse_add_one_section(struct zone *zone, unsigned long start_pfn,
int nr_pages);
+extern void sparse_remove_one_section(struct zone *zone,
+ unsigned long section_nr);

#endif /* __LINUX_MEMORY_HOTPLUG_H */



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