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authorKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>2008-09-02 14:35:58 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2008-09-02 19:21:38 -0700
commitb954185214c3b562c3fcc651e9ec69d421d76bfa (patch)
tree421839b6156b00b258d7bc3b55961fd7e68aa7be /mm/quicklist.c
parent4b8561521dbaa3d766b198496b220e984e3bf756 (diff)
downloadlinux-linaro-stable-b954185214c3b562c3fcc651e9ec69d421d76bfa.tar.gz
mm: size of quicklists shouldn't be proportional to the number of CPUs
Quicklists store pages for each CPU as caches. (Each CPU can cache node_free_pages/16 pages) It is used for page table cache. exit() will increase the cache size, while fork() consumes it. So for example if an apache-style application runs (one parent and many child model), one CPU process will fork() while another CPU will process the middleware work and exit(). At that time, the CPU on which the parent runs doesn't have page table cache at all. Others (on which children runs) have maximum caches. QList_max = (#ofCPUs - 1) x Free / 16 => QList_max / (Free + QList_max) = (#ofCPUs - 1) / (16 + #ofCPUs - 1) So, How much quicklist memory is used in the maximum case? This is proposional to # of CPUs because the limit of per cpu quicklist cache doesn't see the number of cpus. Above calculation mean Number of CPUs per node 2 4 8 16 ============================== ==================== QList_max / (Free + QList_max) 5.8% 16% 30% 48% Wow! Quicklist can spend about 50% memory at worst case. My demonstration program is here -------------------------------------------------------------------------------- #define _GNU_SOURCE #include <stdio.h> #include <errno.h> #include <stdlib.h> #include <string.h> #include <sched.h> #include <unistd.h> #include <sys/mman.h> #include <sys/wait.h> #define BUFFSIZE 512 int max_cpu(void) /* get max number of logical cpus from /proc/cpuinfo */ { FILE *fd; char *ret, buffer[BUFFSIZE]; int cpu = 1; fd = fopen("/proc/cpuinfo", "r"); if (fd == NULL) { perror("fopen(/proc/cpuinfo)"); exit(EXIT_FAILURE); } while (1) { ret = fgets(buffer, BUFFSIZE, fd); if (ret == NULL) break; if (!strncmp(buffer, "processor", 9)) cpu = atoi(strchr(buffer, ':') + 2); } fclose(fd); return cpu; } void cpu_bind(int cpu) /* bind current process to one cpu */ { cpu_set_t mask; int ret; CPU_ZERO(&mask); CPU_SET(cpu, &mask); ret = sched_setaffinity(0, sizeof(mask), &mask); if (ret == -1) { perror("sched_setaffinity()"); exit(EXIT_FAILURE); } sched_yield(); /* not necessary */ } #define MMAP_SIZE (10 * 1024 * 1024) /* 10 MB */ #define FORK_INTERVAL 1 /* 1 second */ main(int argc, char *argv[]) { int cpu_max, nextcpu; long pagesize; pid_t pid; /* set max number of logical cpu */ if (argc > 1) cpu_max = atoi(argv[1]) - 1; else cpu_max = max_cpu(); /* get the page size */ pagesize = sysconf(_SC_PAGESIZE); if (pagesize == -1) { perror("sysconf(_SC_PAGESIZE)"); exit(EXIT_FAILURE); } /* prepare parent process */ cpu_bind(0); nextcpu = cpu_max; loop: /* select destination cpu for child process by round-robin rule */ if (++nextcpu > cpu_max) nextcpu = 1; pid = fork(); if (pid == 0) { /* child action */ char *p; int i; /* consume page tables */ p = mmap(0, MMAP_SIZE, PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, 0, 0); i = MMAP_SIZE / pagesize; while (i-- > 0) { *p = 1; p += pagesize; } /* move to other cpu */ cpu_bind(nextcpu); /* printf("a child moved to cpu%d after mmap().\n", nextcpu); fflush(stdout); */ /* back page tables to pgtable_quicklist */ exit(0); } else if (pid > 0) { /* parent action */ sleep(FORK_INTERVAL); waitpid(pid, NULL, WNOHANG); } goto loop; } ---------------------------------------- When above program which does task migration runs, my 8GB box spends 800MB of memory for quicklist. This is not memory leak but doesn't seem good. % cat /proc/meminfo MemTotal: 7701568 kB MemFree: 4724672 kB (snip) Quicklists: 844800 kB because - My machine spec is number of numa node: 2 number of cpus: 8 (4CPU x2 node) total mem: 8GB (4GB x2 node) free mem: about 5GB - Then, 4.7GB x 16% ~= 880MB. So, Quicklist can use 800MB. So, if following spec machine run that program CPUs: 64 (8cpu x 8node) Mem: 1TB (128GB x8node) Then, quicklist can waste 300GB (= 1TB x 30%). It is too large. So, I don't like cache policies which is proportional to # of cpus. My patch changes the number of caches from: per-cpu-cache-amount = memory_on_node / 16 to per-cpu-cache-amount = memory_on_node / 16 / number_of_cpus_on_node. Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Keiichiro Tokunaga <tokunaga.keiich@jp.fujitsu.com> Acked-by: Christoph Lameter <cl@linux-foundation.org> Tested-by: David Miller <davem@davemloft.net> Acked-by: Mike Travis <travis@sgi.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/quicklist.c')
-rw-r--r--mm/quicklist.c9
1 files changed, 8 insertions, 1 deletions
diff --git a/mm/quicklist.c b/mm/quicklist.c
index 3f703f7cb398..8dbb6805ef35 100644
--- a/mm/quicklist.c
+++ b/mm/quicklist.c
@@ -26,7 +26,10 @@ DEFINE_PER_CPU(struct quicklist, quicklist)[CONFIG_NR_QUICK];
static unsigned long max_pages(unsigned long min_pages)
{
unsigned long node_free_pages, max;
- struct zone *zones = NODE_DATA(numa_node_id())->node_zones;
+ int node = numa_node_id();
+ struct zone *zones = NODE_DATA(node)->node_zones;
+ int num_cpus_on_node;
+ node_to_cpumask_ptr(cpumask_on_node, node);
node_free_pages =
#ifdef CONFIG_ZONE_DMA
@@ -38,6 +41,10 @@ static unsigned long max_pages(unsigned long min_pages)
zone_page_state(&zones[ZONE_NORMAL], NR_FREE_PAGES);
max = node_free_pages / FRACTION_OF_NODE_MEM;
+
+ num_cpus_on_node = cpus_weight_nr(*cpumask_on_node);
+ max /= num_cpus_on_node;
+
return max(max, min_pages);
}