Create the 'in_emergency' trigger, to allow userspace to turn access to the
critical pool on and off. The rationale behind this is to ensure that the
critical pool stays full for *actual* emergency situations, and isn't used
for transient, low-mem situations.
-Matt
Create a userspace trigger: /proc/sys/vm/in_emergency that notifies the kernel
that the system is in an emergency state, and allows the kernel to delve into
the 'critical pool' to satisfy __GFP_CRITICAL allocations.
Signed-off-by: Matthew Dobson <[email protected]>
Index: linux-2.6.15-rc5+critical_pool/Documentation/sysctl/vm.txt
===================================================================
--- linux-2.6.15-rc5+critical_pool.orig/Documentation/sysctl/vm.txt 2005-12-13 16:01:57.783326968 -0800
+++ linux-2.6.15-rc5+critical_pool/Documentation/sysctl/vm.txt 2005-12-13 16:02:40.935766800 -0800
@@ -27,6 +27,7 @@ Currently, these files are in /proc/sys/
- laptop_mode
- block_dump
- critical_pages
+- in_emergency
==============================================================
@@ -112,3 +113,12 @@ This is used to force the Linux VM to re
emergency (__GFP_CRITICAL) allocations. Allocations with this flag
MUST succeed.
The number written into this file is the number of pages to reserve.
+
+==============================================================
+
+in_emergency:
+
+This is used to let the Linux VM know that userspace thinks that the system is
+in an emergency situation.
+Writing a non-zero value into this file tells the VM we *are* in an emergency
+situation & writing zero tells the VM we *are not* in an emergency situation.
Index: linux-2.6.15-rc5+critical_pool/include/linux/sysctl.h
===================================================================
--- linux-2.6.15-rc5+critical_pool.orig/include/linux/sysctl.h 2005-12-13 16:02:13.757898464 -0800
+++ linux-2.6.15-rc5+critical_pool/include/linux/sysctl.h 2005-12-13 16:02:40.937766496 -0800
@@ -181,6 +181,7 @@ enum
VM_LEGACY_VA_LAYOUT=27, /* legacy/compatibility virtual address space layout */
VM_SWAP_TOKEN_TIMEOUT=28, /* default time for token time out */
VM_CRITICAL_PAGES=29, /* # of pages to reserve for __GFP_CRITICAL allocs */
+ VM_IN_EMERGENCY=30, /* tell the VM if we are/aren't in an emergency */
};
Index: linux-2.6.15-rc5+critical_pool/kernel/sysctl.c
===================================================================
--- linux-2.6.15-rc5+critical_pool.orig/kernel/sysctl.c 2005-12-13 16:01:57.784326816 -0800
+++ linux-2.6.15-rc5+critical_pool/kernel/sysctl.c 2005-12-13 16:02:40.942765736 -0800
@@ -859,6 +859,16 @@ static ctl_table vm_table[] = {
.strategy = &sysctl_intvec,
.extra1 = &zero,
},
+ {
+ .ctl_name = VM_IN_EMERGENCY,
+ .procname = "in_emergency",
+ .data = &system_in_emergency,
+ .maxlen = sizeof(system_in_emergency),
+ .mode = 0644,
+ .proc_handler = &proc_dointvec,
+ .strategy = &sysctl_intvec,
+ .extra1 = &zero,
+ },
{ .ctl_name = 0 }
};
Index: linux-2.6.15-rc5+critical_pool/mm/page_alloc.c
===================================================================
--- linux-2.6.15-rc5+critical_pool.orig/mm/page_alloc.c 2005-12-13 16:01:57.810322864 -0800
+++ linux-2.6.15-rc5+critical_pool/mm/page_alloc.c 2005-12-13 16:02:40.946765128 -0800
@@ -53,6 +53,10 @@ unsigned long totalram_pages __read_most
unsigned long totalhigh_pages __read_mostly;
long nr_swap_pages;
+/* Is the sytem in an emergency situation? */
+int system_in_emergency = 0;
+EXPORT_SYMBOL(system_in_emergency);
+
/* The number of pages to maintain in the critical page pool */
int critical_pages = 0;
@@ -927,7 +931,7 @@ struct page * fastcall
__alloc_pages(gfp_t gfp_mask, unsigned int order,
struct zonelist *zonelist)
{
- const gfp_t wait = gfp_mask & __GFP_WAIT;
+ gfp_t wait = gfp_mask & __GFP_WAIT;
struct zone **z;
struct page *page;
struct reclaim_state reclaim_state;
@@ -936,6 +940,16 @@ __alloc_pages(gfp_t gfp_mask, unsigned i
int alloc_flags;
int did_some_progress;
+ if (is_emergency_alloc(gfp_mask)) {
+ /*
+ * If the system is 'in emergency' and this is a critical
+ * allocation, then make sure we don't sleep
+ */
+ gfp_mask &= ~__GFP_WAIT;
+ gfp_mask |= __GFP_HIGH;
+ wait = 0;
+ }
+
might_sleep_if(wait);
restart:
@@ -1070,7 +1084,7 @@ nopage:
* Rather than fail one of these allocations, take a page,
* if there are any, from the critical pool.
*/
- if ((gfp_mask & __GFP_CRITICAL) && !order) {
+ if (is_emergency_alloc(gfp_mask) && !order) {
page = get_critical_page(gfp_mask);
if (page)
goto got_pg;
Index: linux-2.6.15-rc5+critical_pool/include/linux/mm.h
===================================================================
--- linux-2.6.15-rc5+critical_pool.orig/include/linux/mm.h 2005-12-13 16:01:57.783326968 -0800
+++ linux-2.6.15-rc5+critical_pool/include/linux/mm.h 2005-12-13 16:02:40.950764520 -0800
@@ -33,6 +33,12 @@ extern int sysctl_legacy_va_layout;
#endif
extern int critical_pages;
+extern int system_in_emergency;
+
+static inline int is_emergency_alloc(gfp_t gfpmask)
+{
+ return system_in_emergency && (gfpmask & __GFP_CRITICAL);
+}
#include <asm/page.h>
#include <asm/pgtable.h>
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