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SubjectRe: [PATCH] mm:workingset use real time to judge activity of the file page
On Thu, Apr 04, 2019 at 11:30:17AM +0800, Zhaoyang Huang wrote:
> +++ b/mm/workingset.c
> @@ -159,7 +159,7 @@
> NODES_SHIFT + \
> MEM_CGROUP_ID_SHIFT)
> #define EVICTION_MASK (~0UL >> EVICTION_SHIFT)
> -
> +#define EVICTION_JIFFIES (BITS_PER_LONG >> 3)
> /*
> * Eviction timestamps need to be able to cover the full range of
> * actionable refaults. However, bits are tight in the radix tree
> @@ -175,18 +175,22 @@ static void *pack_shadow(int memcgid, pg_data_t *pgdat, unsigned long eviction)
> eviction >>= bucket_order;
> eviction = (eviction << MEM_CGROUP_ID_SHIFT) | memcgid;
> eviction = (eviction << NODES_SHIFT) | pgdat->node_id;
> + eviction = (eviction << EVICTION_JIFFIES) | (jiffies >> EVICTION_JIFFIES);
> eviction = (eviction << RADIX_TREE_EXCEPTIONAL_SHIFT);

... this isn't against current, or even 5.0.

> entry >>= RADIX_TREE_EXCEPTIONAL_SHIFT;
> + entry >>= EVICTION_JIFFIES;
> + prev_jiff = (entry & ((1UL << EVICTION_JIFFIES) - 1)) << EVICTION_JIFFIES;

These two lines are in the wrong order. So you're getting (effectively) a
random answer in your 'prev_jiff', which means your testing isn't thorough
enough. I suspect you're only testing cases you're expecting to improve,
and you aren't testing to make sure that other cases don't regress.

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