memcg: do not replicate get_mem_cgroup_from_mm in __mem_cgroup_try_charge
__mem_cgroup_try_charge duplicates get_mem_cgroup_from_mm for charges which came without a memcg. The only reason seems to be a tiny optimization when css_tryget is not called if the charge can be consumed from the stock. Nevertheless css_tryget is very cheap since it has been reworked to use per-cpu counting so this optimization doesn't give us anything these days. So let's drop the code duplication so that the code is more readable. Signed-off-by: Michal Hocko <mhocko@suse.cz> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -2697,52 +2697,14 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm,
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again:
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again:
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if (*ptr) { /* css should be a valid one */
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if (*ptr) { /* css should be a valid one */
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memcg = *ptr;
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memcg = *ptr;
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if (mem_cgroup_is_root(memcg))
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goto done;
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if (consume_stock(memcg, nr_pages))
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goto done;
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css_get(&memcg->css);
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css_get(&memcg->css);
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} else {
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} else {
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struct task_struct *p;
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memcg = get_mem_cgroup_from_mm(mm);
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rcu_read_lock();
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p = rcu_dereference(mm->owner);
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/*
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* Because we don't have task_lock(), "p" can exit.
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* In that case, "memcg" can point to root or p can be NULL with
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* race with swapoff. Then, we have small risk of mis-accouning.
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* But such kind of mis-account by race always happens because
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* we don't have cgroup_mutex(). It's overkill and we allo that
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* small race, here.
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* (*) swapoff at el will charge against mm-struct not against
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* task-struct. So, mm->owner can be NULL.
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*/
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memcg = mem_cgroup_from_task(p);
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if (!memcg)
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memcg = root_mem_cgroup;
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if (mem_cgroup_is_root(memcg)) {
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rcu_read_unlock();
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goto done;
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}
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if (consume_stock(memcg, nr_pages)) {
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/*
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* It seems dagerous to access memcg without css_get().
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* But considering how consume_stok works, it's not
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* necessary. If consume_stock success, some charges
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* from this memcg are cached on this cpu. So, we
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* don't need to call css_get()/css_tryget() before
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* calling consume_stock().
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*/
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rcu_read_unlock();
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goto done;
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}
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/* after here, we may be blocked. we need to get refcnt */
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if (!css_tryget(&memcg->css)) {
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rcu_read_unlock();
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goto again;
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}
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rcu_read_unlock();
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}
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}
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if (mem_cgroup_is_root(memcg))
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goto done;
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if (consume_stock(memcg, nr_pages))
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goto done;
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do {
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do {
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bool invoke_oom = oom && !nr_oom_retries;
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bool invoke_oom = oom && !nr_oom_retries;
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@ -2778,8 +2740,8 @@ again:
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if (batch > nr_pages)
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if (batch > nr_pages)
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refill_stock(memcg, batch - nr_pages);
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refill_stock(memcg, batch - nr_pages);
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css_put(&memcg->css);
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done:
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done:
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css_put(&memcg->css);
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*ptr = memcg;
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*ptr = memcg;
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return 0;
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return 0;
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nomem:
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nomem:
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