CMA and zone watermarks

Rabin Vincent
2012-10-08T15:41:55Z

[-- Attachment #1: Type: text/plain, Size: 1235 bytes --]

It appears that when CMA is enabled, the zone watermarks are not properly
respected, leading to for example GFP_NOWAIT allocations getting access to the
high pools.

I ran the following test code which simply allocates pages with GFP_NOWAIT
until it fails, and then tries GFP_ATOMIC. Without CMA, the GFP_ATOMIC
allocation succeeds, with CMA, it fails too.

Logs attached (includes my patch which prints the migration type in the failure
message http://marc.info/?l=linux-mm&m=134971041701306&w=2), taken on 3.6
kernel.

Thanks.

diff --git a/arch/arm/mach-ux500/board-mop500.c
b/arch/arm/mach-ux500/board-mop500.c
index a534d88..b98d0df 100644
--- a/arch/arm/mach-ux500/board-mop500.c
+++ b/arch/arm/mach-ux500/board-mop500.c
@@ -854,3 +854,25 @@ DT_MACHINE_START(U8500_DT, "ST-Ericsson U8500
platform (Device Tree Support)")
.dt_compat = u8500_dt_board_compat,
MACHINE_END
#endif
+
+static int __init late(void)
+{
+ while (1) {
+ void *p;
+
+ p = alloc_page(GFP_NOWAIT);
+ if (!p) {
+ pr_err("GFP_NOWAIT failed, checking GFP_ATOMIC");
+
+ p = alloc_page(GFP_ATOMIC);
+ if (!p)
+ panic("GFP_ATOMIC failed too, fail!");
+
+ panic("GFP_ATOMIC OK, all good\n");
+ }
+
+ }
+
+ return 0;
+}
+late_initcall(late);

[-- Attachment #2: cmalog.txt.gz --]
[-- Type: application/x-gzip, Size: 6122 bytes --]