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SubjectRe: [-mm PATCH] register_memory/unregister_memory clean ups
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On Tue, 2008-02-12 at 14:15 -0800, Dave Hansen wrote:
> On Tue, 2008-02-12 at 14:07 -0800, Badari Pulavarty wrote:
> > On Tue, 2008-02-12 at 13:57 -0800, Dave Hansen wrote:
> > > On Tue, 2008-02-12 at 13:56 -0800, Badari Pulavarty wrote:
> > > >
> > > > +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);
> > > > +}
> > >
> > > I do think passing in a mem_section* here is highly superior. It makes
> > > it impossible to pass a pfn in and not get a warning.
> > >
> >
> > Only problem is, I need to hold pgdat_resize_lock() if pass *ms.
> > If I don't hold the resize_lock, I have to re-evaluate.
>
> What's wrong with holding the resize lock? What races, precisely, are
> you trying to avoid?
>
> > And also,
> > I need to pass section_nr for decoding the mem_map anyway :(
>
> See sparse.c::__section_nr(). It takes a mem_section* and returns a
> section_nr.

Here is the version with your suggestion. Do you like this better ?

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.

Signed-off-by: Badari Pulavarty <pbadari@us.ibm.com>

---
include/linux/memory_hotplug.h | 4 ++++
mm/memory_hotplug.c | 34 ++++++++++++++++++++++++++++++++++
mm/sparse.c | 39 ++++++++++++++++++++++++++++++++++++---
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 14:49:07.000000000 -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, struct mem_section *ms)
+{
+ if (!valid_section(ms))
+ return;
+
+ unregister_memory_section(ms);
+ sparse_remove_one_section(zone, ms);
+}
+
/*
* Reasonably generic function for adding memory. It is
* expected that archs that support memory hotplug will
@@ -135,6 +144,31 @@ 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;
+ unsigned long flags;
+ struct pglist_data *pgdat = zone->zone_pgdat;
+
+ /*
+ * 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;
+ pgdat_resize_lock(pgdat, &flags);
+ __remove_section(zone, pfn_to_section(pfn));
+ pgdat_resize_unlock(pgdat, &flags);
+ }
+}
+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 14:51:07.000000000 -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 +416,36 @@ out:
}
return ret;
}
+
+void sparse_remove_one_section(struct zone *zone, struct mem_section *ms)
+{
+ struct page *memmap = NULL;
+ unsigned long *usemap = NULL;
+ unsigned long flags;
+
+ if (ms->section_mem_map) {
+ usemap = ms->pageblock_flags;
+ memmap = sparse_decode_mem_map(ms->section_mem_map,
+ __section_nr(ms));
+ ms->section_mem_map = 0;
+ ms->pageblock_flags = NULL;
+ }
+
+ /*
+ * 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 14:54:40.000000000 -0800
@@ -8,6 +8,7 @@
struct page;
struct zone;
struct pglist_data;
+struct mem_section;

#ifdef CONFIG_MEMORY_HOTPLUG
/*
@@ -64,6 +65,8 @@ 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 +191,6 @@ 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, struct mem_section *ms);

#endif /* __LINUX_MEMORY_HOTPLUG_H */



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