Hello.
On Wed, Dec 04, 2024 at 02:44:01PM +0100, Maarten Lankhorst <dev@xxxxxxxxxxxx> wrote:
> +bool dmem_cgroup_state_evict_valuable(struct dmem_cgroup_pool_state *limit_pool,
> + struct dmem_cgroup_pool_state *test_pool,
> + bool ignore_low, bool *ret_hit_low)
> +{
> + struct dmem_cgroup_pool_state *pool = test_pool;
> + struct page_counter *climit, *ctest;
> + u64 used, min, low;
> +
> + /* Can always evict from current pool, despite limits */
> + if (limit_pool == test_pool)
> + return true;
> +
> + if (limit_pool) {
> + if (!parent_dmemcs(limit_pool->cs))
> + return true;
> +
> + for (pool = test_pool; pool && limit_pool != pool; pool = pool_parent(pool))
> + {}
> +
> + if (!pool)
> + return false;
> + } else {
> + /*
> + * If there is no cgroup limiting memory usage, use the root
> + * cgroup instead for limit calculations.
> + */
> + for (limit_pool = test_pool; pool_parent(limit_pool); limit_pool = pool_parent(limit_pool))
> + {}
> + }
I'm trying to understand the two branches above. If limit_pool is a root
one, eviction is granted and no protection is evaluated.
Then it checks that test_pool is below limit_pool (can this ever fail,
given the limit_pool must have been above when charging in test_pool?).
(OK, this may be called arbitrarily by modules.)
I think it could be simplified and corrected like this:
/* Resolve NULL limit_pool */
if (!limit_pool)
for (limit_pool = test_pool; pool_parent(limit_pool); limit_pool = pool_parent(limit_pool));
/* Check ancestry */
if (!cgroup_is_descendant(test_pool->cs->css.cgroup, limit_pool->cs->css.cgroup))
return false;
HTH,
Michal
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