[RFC][PATCH 2/8] Create emergency trigger

Matthew Dobson
2005-11-18T19:36:57Z

[-- Attachment #1: Type: text/plain, Size: 40 bytes --]

Create the in_emergency trigger.

-Matt

[-- Attachment #2: emergency_trigger.patch --]
[-- Type: text/x-patch, Size: 4892 bytes --]

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 <colpatch@us.ibm.com>

Index: linux-2.6.15-rc1+critical_pool/Documentation/sysctl/vm.txt
===================================================================
--- linux-2.6.15-rc1+critical_pool.orig/Documentation/sysctl/vm.txt 2005-11-17 16:51:19.000000000 -0800
+++ linux-2.6.15-rc1+critical_pool/Documentation/sysctl/vm.txt 2005-11-17 16:51:20.000000000 -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-rc1+critical_pool/include/linux/sysctl.h
===================================================================
--- linux-2.6.15-rc1+critical_pool.orig/include/linux/sysctl.h 2005-11-17 16:51:19.000000000 -0800
+++ linux-2.6.15-rc1+critical_pool/include/linux/sysctl.h 2005-11-17 16:51:20.000000000 -0800
@@ -182,6 +182,7 @@ 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=30, /* # of pages to reserve for __GFP_CRITICAL allocs */
+ VM_IN_EMERGENCY=31, /* tell the VM if we are/aren't in an emergency */
};

Index: linux-2.6.15-rc1+critical_pool/kernel/sysctl.c
===================================================================
--- linux-2.6.15-rc1+critical_pool.orig/kernel/sysctl.c 2005-11-17 16:51:19.000000000 -0800
+++ linux-2.6.15-rc1+critical_pool/kernel/sysctl.c 2005-11-17 16:51:20.000000000 -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-rc1+critical_pool/mm/page_alloc.c
===================================================================
--- linux-2.6.15-rc1+critical_pool.orig/mm/page_alloc.c 2005-11-17 16:51:19.000000000 -0800
+++ linux-2.6.15-rc1+critical_pool/mm/page_alloc.c 2005-11-18 11:24:02.024254248 -0800
@@ -53,6 +53,9 @@ 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;
+
/* The number of pages to maintain in the critical page pool */
int critical_pages = 0;

@@ -865,7 +868,7 @@ 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 **zones, *z;
struct page *page;
struct reclaim_state reclaim_state;
@@ -876,6 +879,16 @@ __alloc_pages(gfp_t gfp_mask, unsigned i
int can_try_harder;
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_NORECLAIM | __GFP_HIGH;
+ wait = 0;
+ }
+
might_sleep_if(wait);

/*
@@ -1053,7 +1066,7 @@ nopage:
* Rather than fail one of these allocations, take a page (if any)
* from the critical pool.
*/
- if (gfp_mask & __GFP_CRITICAL) {
+ if (is_emergency_alloc(gfp_mask)) {
page = get_critical_page(gfp_mask);
if (page) {
z = page_zone(page);
Index: linux-2.6.15-rc1+critical_pool/include/linux/mm.h
===================================================================
--- linux-2.6.15-rc1+critical_pool.orig/include/linux/mm.h 2005-11-17 16:51:19.000000000 -0800
+++ linux-2.6.15-rc1+critical_pool/include/linux/mm.h 2005-11-17 16:51:20.000000000 -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>