also quick review to lowmemorykiller.c
> #include <linux/module.h>
> #include <linux/kernel.h>
> #include <linux/mm.h>
> #include <linux/oom.h>
> #include <linux/sched.h>
>
> static int lowmem_shrink(int nr_to_scan, gfp_t gfp_mask);
>
> static struct shrinker lowmem_shrinker = {
> .shrink = lowmem_shrink,
> .seeks = DEFAULT_SEEKS * 16
> };
why do you choice *16?
> static uint32_t lowmem_debug_level = 2;
> static int lowmem_adj[6] = {
why do you choice [6]?
> 0,
> 1,
> 6,
> 12,
> };
>
> static int lowmem_adj_size = 4;
> static size_t lowmem_minfree[6] = {
> 3*512, // 6MB
> 2*1024, // 8MB
> 4*1024, // 16MB
> 16*1024, // 64MB
> };
> static int lowmem_minfree_size = 4;
>
> #define lowmem_print(level, x...) do { if(lowmem_debug_level >= (level))
> printk(x); } while(0)
>
> module_param_named(cost, lowmem_shrinker.seeks, int, S_IRUGO | S_IWUSR);
> module_param_array_named(adj, lowmem_adj, int, &lowmem_adj_size, S_IRUGO |
> S_IWUSR);
> module_param_array_named(minfree, lowmem_minfree, uint, &lowmem_minfree_size,
> S_IRUGO | S_IWUSR);
> module_param_named(debug_level, lowmem_debug_level, uint, S_IRUGO | S_IWUSR);
>
> static int lowmem_shrink(int nr_to_scan, gfp_t gfp_mask)
> {
> struct task_struct *p;
> struct task_struct *selected = NULL;
> int rem = 0;
> int tasksize;
> int i;
> int min_adj = OOM_ADJUST_MAX + 1;
> int selected_tasksize = 0;
> int array_size = ARRAY_SIZE(lowmem_adj);
> int other_free = global_page_state(NR_FREE_PAGES) +
> global_page_state(NR_FILE_PAGES);
I think you don't consider mlocked page (and/or other unevictable page).
if much mlocked file page exist, other_free can become large value.
then, this routine don't kill any process.
> if(lowmem_adj_size < array_size)
> array_size = lowmem_adj_size;
> if(lowmem_minfree_size < array_size)
> array_size = lowmem_minfree_size;
> for(i = 0; i < array_size; i++) {
> if(other_free < lowmem_minfree[i]) {
> min_adj = lowmem_adj[i];
> break;
> }
> }
>
>
> if(nr_to_scan > 0)
> lowmem_print(3, "lowmem_shrink %d, %x, ofree %d, ma %d\n",
> nr_to_scan, gfp_mask, other_fr> ee, min_adj);
> read_lock(&tasklist_lock);
> for_each_process(p) {
Oops. too long locking.
shrink_slab() is freqentlly called function. I don't like costly operation.
> if(p->oomkilladj >= 0 && p->mm) {
> tasksize = get_mm_rss(p->mm);
> if(nr_to_scan > 0 && tasksize > 0 && p->oomkilladj >=
> min_adj) {
> if(selected == NULL ||
> p->oomkilladj > selected->oomkilladj ||
> (p->oomkilladj == selected->oomkilladj &&
> tasksize > selected_tasksize)) {
> selected = p;
> selected_tasksize = tasksize;
> lowmem_print(2, "select %d (%s), adj
> %d, size %d, to kill\n",
> p->pid, p->comm,
> p->oomkilladj, tasksize);
> }
> }
> rem += tasksize;
this code mean,
shrinker->shrink(0, gfp_mask) indicate to recalculate total rss every time.
it is too CPU and battery wasting.
> }
> }
> if(selected != NULL) {
> lowmem_print(1, "send sigkill to %d (%s), adj %d, size %d\n",
> selected->pid, selected->comm,
> selected->oomkilladj, selected_tasksize);
> force_sig(SIGKILL, selected);
> rem -= selected_tasksize;
> }
> lowmem_print(4, "lowmem_shrink %d, %x, return %d\n", nr_to_scan,
> gfp_mask, rem);
> read_unlock(&tasklist_lock);
> return rem;
> }
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