* Re: sparsemem support on MIPS
2010-08-19 23:06 ` David VomLehn
@ 2010-08-19 23:19 ` Jon Fraser
2010-08-19 23:29 ` Michael Sundius
1 sibling, 0 replies; 4+ messages in thread
From: Jon Fraser @ 2010-08-19 23:19 UTC (permalink / raw)
To: David VomLehn
Cc: jfraser, naveen yadav, Ralf Baechle, linux-mips@linux-mips.org,
sshtylyov@mvista.com, Michael Sundius
On Thu, 2010-08-19 at 16:06 -0700, David VomLehn wrote:
> On Thu, Aug 19, 2010 at 09:04:21PM +0530, naveen yadav wrote:
> >
> > Dear all,
> >
> > I build MIPS 32 with sparsemem support to take care of holes in
> > physical memory, this conserve memory but put overhead to speed
> > because of pointer redirection in pfn_to_page().
> >
> > To prevent this conversion I tried to use
> > CONFIG_SPARSEMEM_VMEMMAP_ENABLE on MIPS 32 but kernel build fails
> > becauase most of the supported functions related to vmemmap are
> > supported for 64 bit architectures only.
> >
> > I wish to compare memory and speed result with / without
> > CONFIG_SPARSEMEM_VMEMMAP_ENABLE in MIPS 32. I need your comment in it
> > ?
>
> We use sparse memory and submitted a patch some while ago to add support,
> but it died for lack of interest. The patch was relative to a kernel
> from several released ago; I don't know whether it would apply to
> the tip. I can see if I track it down.
I keep thinking we should have a git tree for highmem 'experimental'
changes. Some of us are shipping highmem, discontiguous memory systems
in high volume.
--jfraser
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: sparsemem support on MIPS
2010-08-19 23:06 ` David VomLehn
2010-08-19 23:19 ` Jon Fraser
@ 2010-08-19 23:29 ` Michael Sundius
1 sibling, 0 replies; 4+ messages in thread
From: Michael Sundius @ 2010-08-19 23:29 UTC (permalink / raw)
To: David VomLehn; +Cc: naveen yadav, Ralf Baechle, linux-mips, sshtylyov
David VomLehn wrote:
> On Thu, Aug 19, 2010 at 09:04:21PM +0530, naveen yadav wrote:
>
>> Dear all,
>>
>> I build MIPS 32 with sparsemem support to take care of holes in
>> physical memory, this conserve memory but put overhead to speed
>> because of pointer redirection in pfn_to_page().
>>
>> To prevent this conversion I tried to use
>> CONFIG_SPARSEMEM_VMEMMAP_ENABLE on MIPS 32 but kernel build fails
>> becauase most of the supported functions related to vmemmap are
>> supported for 64 bit architectures only.
>>
>> I wish to compare memory and speed result with / without
>> CONFIG_SPARSEMEM_VMEMMAP_ENABLE in MIPS 32. I need your comment in it
>> ?
>>
>
> We use sparse memory and submitted a patch some while ago to add support,
> but it died for lack of interest. The patch was relative to a kernel
> from several released ago; I don't know whether it would apply to
> the tip. I can see if I track it down.
>
Please find my original patch below. Note that we also tried to use the
virtually mapped
sparsemem but failed.
for the vmemmap sparse support, one thing I found was you need to do
paging_init() before sparse_init(). I also made lots of changes
to arch/mips/mm/init.c (some specific to our own changes others generic)
and moved a few things in header files around.
I can probably (tomorrow) create a patch of my changes that I made (that
never worked) for the vmemmap support. I'd love to revisit this
one find day and get it to actually work, but I seemed at the time to
get stuck without any clue how to move it forward.
some collaboration would be greatfully appreciated.
Mike
Looks great to me. I can't test it, of course, but I don't see any
problems with it.
Signed-off-by: Dave Hansen <dave@linux.vnet.ibm.com>
-- Dave
> Otherwise it looks good to me. I see from the rest of the thread that
> there is some discussion over the sizes of these, with that sorted.
>
> Acked-by: Andy Whitcroft <apw@shadowen.org>
>
> -apw
>
attached is my most recent patch with I *think* everyones requests for it.
------------------------------------------------------------------------
diff --git a/Documentation/sparsemem.txt b/Documentation/sparsemem.txt
new file mode 100644
index 0000000..0b36412
--- /dev/null
+++ b/Documentation/sparsemem.txt
@@ -0,0 +1,92 @@
+Sparsemem divides up physical memory in your system into N sections of M
+bytes. Page tables are created for only those sections that
+actually exist (as far as the sparsemem code is concerned). This allows
+for holes in the physical memory without having to waste space by
+creating page descriptors for those pages that do not exist.
+When page_to_pfn() or pfn_to_page() are called there is a bit of overhead to
+look up the proper memory section to get to the page_table, but this
+is small compared to the memory you are likely to save. So, it's not the
+default, but should be used if you have big holes in physical memory.
+
+Note that discontiguous memory is more closely related to NUMA machines
+and if you are a single CPU system use sparsemem and not discontig.
+It's much simpler.
+
+1) CALL MEMORY_PRESENT()
+Existing sections are recorded once the bootmem allocator is up and running by
+calling the sparsemem function "memory_present(node, pfn_start, pfn_end)" for each
+block of memory that exists in your physical address space. The
+memory_present() function records valid sections in a data structure called
+mem_section[].
+
+2) DETERMINE AND SET THE SIZE OF SECTIONS AND PHYSMEM
+The size of N and M above depend upon your architecture
+and your platform and are specified in the file:
+
+ include/asm-<your_arch>/sparsemem.h
+
+and you should create the following lines similar to below:
+
+ #ifdef CONFIG_YOUR_PLATFORM
+ #define SECTION_SIZE_BITS 27 /* 128 MiB */
+ #endif
+ #define MAX_PHYSMEM_BITS 31 /* 2 GiB */
+
+if they don't already exist, where:
+
+ * SECTION_SIZE_BITS 2^M: how big each section will be
+ * MAX_PHYSMEM_BITS 2^N: how much memory we can have in that
+ space
+
+3) INITIALIZE SPARSE MEMORY
+You should make sure that you initialize the sparse memory code by calling
+
+ bootmem_init();
+ + sparse_init();
+ paging_init();
+
+just before you call paging_init() and after the bootmem_allocator is
+turned on in your setup_arch() code.
+
+4) ENABLE SPARSEMEM IN KCONFIG
+Add a line like this:
+
+ select ARCH_SPARSEMEM_ENABLE
+
+into the config for your platform in arch/<your_arch>/Kconfig. This will
+ensure that turning on sparsemem is enabled for your platform.
+
+5) CONFIG
+Run make *config, as you like, and turn on the sparsemem
+memory model under the "Kernel Type" --> "Memory Model" and then build your
+kernel.
+
+
+6) Gotchas
+
+One trick that I encountered when I was turning this on for MIPS was that there
+was some code in mem_init() that set the "reserved" flag for pages that were not
+valid RAM. This caused my kernel to crash when I enabled sparsemem since those
+pages (and page descriptors) didn't actually exist. I changed my code by adding
+lines like below:
+
+
+ for (tmp = highstart_pfn; tmp < highend_pfn; tmp++) {
+ struct page *page = pfn_to_page(tmp);
+
+ + if (!pfn_valid(tmp))
+ + continue;
+ +
+ if (!page_is_ram(tmp)) {
+ SetPageReserved(page);
+ continue;
+ }
+ ClearPageReserved(page);
+ init_page_count(page);
+ __free_page(page);
+ physmem_record(PFN_PHYS(tmp), PAGE_SIZE, physmem_highmem);
+ totalhigh_pages++;
+ }
+
+
+Once I got that straight, it worked!!!! I saved 10MiB of memory.
diff --git a/arch/mips/kernel/setup.c b/arch/mips/kernel/setup.c
index f8a535a..6ff0f72 100644
--- a/arch/mips/kernel/setup.c
+++ b/arch/mips/kernel/setup.c
@@ -405,7 +405,6 @@ static void __init bootmem_init(void)
/* Register lowmem ranges */
free_bootmem(PFN_PHYS(start), size << PAGE_SHIFT);
- memory_present(0, start, end);
}
/*
@@ -417,6 +416,23 @@ static void __init bootmem_init(void)
* Reserve initrd memory if needed.
*/
finalize_initrd();
+
+ /* call memory present for all the ram */
+ for (i = 0; i < boot_mem_map.nr_map; i++) {
+ unsigned long start, end;
+
+ /*
+ * * memory present only usable memory.
+ * */
+ if (boot_mem_map.map[i].type != BOOT_MEM_RAM)
+ continue;
+
+ start = PFN_UP(boot_mem_map.map[i].addr);
+ end = PFN_DOWN(boot_mem_map.map[i].addr
+ + boot_mem_map.map[i].size);
+
+ memory_present(0, start, end);
+ }
}
#endif /* CONFIG_SGI_IP27 */
diff --git a/arch/mips/mm/init.c b/arch/mips/mm/init.c
index 480dec0..9bc6d35 100644
--- a/arch/mips/mm/init.c
+++ b/arch/mips/mm/init.c
@@ -417,6 +417,9 @@ void __init mem_init(void)
for (tmp = highstart_pfn; tmp < highend_pfn; tmp++) {
struct page *page = pfn_to_page(tmp);
+ if (!pfn_valid(tmp))
+ continue;
+
if (!page_is_ram(tmp)) {
SetPageReserved(page);
continue;
diff --git a/include/asm-mips/sparsemem.h b/include/asm-mips/sparsemem.h
index 795ac6c..67245cb 100644
--- a/include/asm-mips/sparsemem.h
+++ b/include/asm-mips/sparsemem.h
@@ -6,7 +6,7 @@
* SECTION_SIZE_BITS 2^N: how big each section will be
* MAX_PHYSMEM_BITS 2^N: how much memory we can have in that space
*/
-#define SECTION_SIZE_BITS 28
+#define SECTION_SIZE_BITS 27
#define MAX_PHYSMEM_BITS 35
#endif /* CONFIG_SPARSEMEM */
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