[PATCH v3] xen: arm32: reduce default size of the xenheap

* [PATCH v3] xen: arm32: reduce default size of the xenheap
@ 2015-02-19 17:39 Ian Campbell
  2015-02-19 18:57 ` Julien Grall
  0 siblings, 1 reply; 3+ messages in thread
From: Ian Campbell @ 2015-02-19 17:39 UTC (permalink / raw)
  To: xen-devel
  Cc: Ian Campbell, stefano.stabellini, julien.grall, tim, Jan Beulich,
	Jintack Lim

... and make it tunable via the command line.

1/8 of RAM is 128M on a 1GB system and 256M on a 2GB system etc,
which is a lot. 1/32 of RAM seems more reasonable. Also drop the
minimum to 32M.

Leave the maximum at 1GB.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Cc: Jintack Lim <jintack@cs.columbia.edu>
Cc: Jan Beulich <JBeulich@suse.com>
---
v3:
 - Clarify doc and comments
 - Enforce new minimum of 32M, not old 128M
 - Only allocate exact amount if user gives a value, rather than
   searching for the next smallest power of two we can find.
v2:
 - Use xenheap_megabytes as the option, which is what older x86 Xen
   used.

I'd like to backport at least the command line option to 4.5. Reducing
the default heap size is a bit border line but I'm inclined to take
it.
---
 docs/misc/xen-command-line.markdown |   11 +++++++++++
 xen/arch/arm/setup.c                |   30 +++++++++++++++++++++---------
 2 files changed, 32 insertions(+), 9 deletions(-)

diff --git a/docs/misc/xen-command-line.markdown b/docs/misc/xen-command-line.markdown
index bc316be..9b458e1 100644
--- a/docs/misc/xen-command-line.markdown
+++ b/docs/misc/xen-command-line.markdown
@@ -237,6 +237,17 @@ and not running softirqs. Reduce this if softirqs are not being run frequently
 enough. Setting this to a high value may cause boot failure, particularly if
 the NMI watchdog is also enabled.
 
+### xenheap\_megabytes (arm32)
+> `= <size>`
+
+> Default: `0` (1/32 of RAM)
+
+Amount of RAM to set aside for the Xenheap.
+
+By default will use 1/32 of the RAM up to a maximum of 1GB and with a
+minimum of 32M, subject to a suitably aligned and sized contiguous
+region of memory being available.
+
 ### clocksource
 > `= pit | hpet | acpi`
 
diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
index a916ca6..9a1c285 100644
--- a/xen/arch/arm/setup.c
+++ b/xen/arch/arm/setup.c
@@ -50,6 +50,11 @@ struct bootinfo __initdata bootinfo;
 
 struct cpuinfo_arm __read_mostly boot_cpu_data;
 
+#ifdef CONFIG_ARM_32
+static unsigned long opt_xenheap_megabytes __initdata;
+integer_param("xenheap_megabytes", opt_xenheap_megabytes);
+#endif
+
 static __used void init_done(void)
 {
     free_init_memory();
@@ -497,20 +502,26 @@ static void __init setup_mm(unsigned long dtb_paddr, size_t dtb_size)
     total_pages = ram_pages = ram_size >> PAGE_SHIFT;
 
     /*
-     * Locate the xenheap using these constraints:
+     * If the user has not requested otherwise via the command line
+     * then locate the xenheap using these constraints:
      *
      *  - must be 32 MiB aligned
      *  - must not include Xen itself or the boot modules
-     *  - must be at most 1GB or 1/8 the total RAM in the system if less
-     *  - must be at least 128M
+     *  - must be at most 1GB or 1/32 the total RAM in the system if less
+     *  - must be at least 32M
      *
      * We try to allocate the largest xenheap possible within these
      * constraints.
      */
     heap_pages = ram_pages;
-    xenheap_pages = (heap_pages/8 + 0x1fffUL) & ~0x1fffUL;
-    xenheap_pages = max(xenheap_pages, 128UL<<(20-PAGE_SHIFT));
-    xenheap_pages = min(xenheap_pages, 1UL<<(30-PAGE_SHIFT));
+    if ( opt_xenheap_megabytes )
+        xenheap_pages = opt_xenheap_megabytes << (20-PAGE_SHIFT);
+    else
+    {
+        xenheap_pages = (heap_pages/32 + 0x1fffUL) & ~0x1fffUL;
+        xenheap_pages = max(xenheap_pages, 32UL<<(20-PAGE_SHIFT));
+        xenheap_pages = min(xenheap_pages, 1UL<<(30-PAGE_SHIFT));
+    }
 
     do
     {
@@ -521,15 +532,16 @@ static void __init setup_mm(unsigned long dtb_paddr, size_t dtb_size)
             break;
 
         xenheap_pages >>= 1;
-    } while ( xenheap_pages > 128<<(20-PAGE_SHIFT) );
+    } while ( !opt_xenheap_megabytes && xenheap_pages > 32<<(20-PAGE_SHIFT) );
 
     if ( ! e )
         panic("Not not enough space for xenheap");
 
     domheap_pages = heap_pages - xenheap_pages;
 
-    printk("Xen heap: %"PRIpaddr"-%"PRIpaddr" (%lu pages)\n",
-            e - (pfn_to_paddr(xenheap_pages)), e, xenheap_pages);
+    printk("Xen heap: %"PRIpaddr"-%"PRIpaddr" (%lu pages%s)\n",
+           e - (pfn_to_paddr(xenheap_pages)), e, xenheap_pages,
+           opt_xenheap_megabytes ? ", from command-line" : "");
     printk("Dom heap: %lu pages\n", domheap_pages);
 
     setup_xenheap_mappings((e >> PAGE_SHIFT) - xenheap_pages, xenheap_pages);
-- 
1.7.10.4

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