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mm/memcg: prepare for swap over-high accounting and penalty calculation

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Patch series "memcg: Slow down swap allocation as the available space
gets depleted", v6.

Tejun describes the problem as follows:

When swap runs out, there's an abrupt change in system behavior - the
anonymous memory suddenly becomes unmanageable which readily breaks any
sort of memory isolation and can bring down the whole system.  To avoid
that, oomd [1] monitors free swap space and triggers kills when it drops
below the specific threshold (e.g.  15%).

While this works, it's far from ideal:

 - Depending on IO performance and total swap size, a given
   headroom might not be enough or too much.

 - oomd has to monitor swap depletion in addition to the usual
   pressure metrics and it currently doesn't consider memory.swap.max.

Solve this by adapting parts of the approach that memory.high uses -
slow down allocation as the resource gets depleted turning the depletion
behavior from abrupt cliff one to gradual degradation observable through
memory pressure metric.

[1] https://github.com/facebookincubator/oomd

This patch (of 4):

Slice the memory overage calculation logic a little bit so we can reuse
it to apply a similar penalty to the swap.  The logic which accesses the
memory-specific fields (use and high values) has to be taken out of
calculate_high_delay().

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Chris Down <chris@chrisdown.name>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Link: http://lkml.kernel.org/r/20200527195846.102707-1-kuba@kernel.org
Link: http://lkml.kernel.org/r/20200527195846.102707-2-kuba@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Jakub Kicinski 2020-06-01 21:49:42 -07:00 committed by Linus Torvalds
parent 54b512e96d
commit 8a5dbc657e
1 changed files with 36 additions and 28 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

64
mm/memcontrol.c
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@ -2321,40 +2321,47 @@ static void high_work_func(struct work_struct *work)
#define MEMCG_DELAY_PRECISION_SHIFT 20
#define MEMCG_DELAY_SCALING_SHIFT 14
static u64 calculate_overage(unsigned long usage, unsigned long high)
{
u64 overage;
if (usage <= high)
return 0;
/*
* Prevent division by 0 in overage calculation by acting as if
* it was a threshold of 1 page
*/
high = max(high, 1UL);
overage = usage - high;
overage <<= MEMCG_DELAY_PRECISION_SHIFT;
return div64_u64(overage, high);
}
static u64 mem_find_max_overage(struct mem_cgroup *memcg)
{
u64 overage, max_overage = 0;
do {
overage = calculate_overage(page_counter_read(&memcg->memory),
READ_ONCE(memcg->high));
max_overage = max(overage, max_overage);
} while ((memcg = parent_mem_cgroup(memcg)) &&
!mem_cgroup_is_root(memcg));
return max_overage;
}
/*
* Get the number of jiffies that we should penalise a mischievous cgroup which
* is exceeding its memory.high by checking both it and its ancestors.
*/
static unsigned long calculate_high_delay(struct mem_cgroup *memcg,
unsigned int nr_pages)
unsigned int nr_pages,
u64 max_overage)
{
unsigned long penalty_jiffies;
u64 max_overage = 0;
do {
unsigned long usage, high;
u64 overage;
usage = page_counter_read(&memcg->memory);
high = READ_ONCE(memcg->high);
if (usage <= high)
continue;
/*
* Prevent division by 0 in overage calculation by acting as if
* it was a threshold of 1 page
*/
high = max(high, 1UL);
overage = usage - high;
overage <<= MEMCG_DELAY_PRECISION_SHIFT;
overage = div64_u64(overage, high);
if (overage > max_overage)
max_overage = overage;
} while ((memcg = parent_mem_cgroup(memcg)) &&
!mem_cgroup_is_root(memcg));
if (!max_overage)
return 0;
@ -2411,7 +2418,8 @@ void mem_cgroup_handle_over_high(void)
* memory.high is breached and reclaim is unable to keep up. Throttle
* allocators proactively to slow down excessive growth.
*/
penalty_jiffies = calculate_high_delay(memcg, nr_pages);
penalty_jiffies = calculate_high_delay(memcg, nr_pages,
mem_find_max_overage(memcg));
/*
* Don't sleep if the amount of jiffies this memcg owes us is so low