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mm: memcontrol: try harder to set a new memory.high

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Setting a memory.high limit below the usage makes almost no effort to
shrink the cgroup to the new target size.

While memory.high is a "soft" limit that isn't supposed to cause OOM
situations, we should still try harder to meet a user request through
persistent reclaim.

For example, after setting a 10M memory.high on an 800M cgroup full of
file cache, the usage shrinks to about 350M:

  + cat /cgroup/workingset/memory.current
  841568256
  + echo 10M
  + cat /cgroup/workingset/memory.current
  355729408

This isn't exactly what the user would expect to happen. Setting the
value a few more times eventually whittles the usage down to what we
are asking for:

  + echo 10M
  + cat /cgroup/workingset/memory.current
  104181760
  + echo 10M
  + cat /cgroup/workingset/memory.current
  31801344
  + echo 10M
  + cat /cgroup/workingset/memory.current
  10440704

To improve this, add reclaim retry loops to the memory.high write()
callback, similar to what we do for memory.max, to make a reasonable
effort that the usage meets the requested size after the call returns.

Afterwards, a single write() to memory.high is enough in all but extreme
cases:

  + cat /cgroup/workingset/memory.current
  841609216
  + echo 10M
  + cat /cgroup/workingset/memory.current
  10182656

790M is not a reasonable reclaim target to ask of a single reclaim
invocation.  And it wouldn't be reasonable to optimize the reclaim code
for it.  So asking for the full size but retrying is not a bad choice
here: we express our intent, and benefit if reclaim becomes better at
handling larger requests, but we also acknowledge that some of the
deltas we can encounter in memory_high_write() are just too ridiculously
big for a single reclaim invocation to manage.

Link: http://lkml.kernel.org/r/20191022201518.341216-2-hannes@cmpxchg.org
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Johannes Weiner 2019-11-30 17:50:09 -08:00 committed by Linus Torvalds
parent 7249c9f01d
commit 8c8c383c04
1 changed files with 24 additions and 6 deletions
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30
mm/memcontrol.c
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@ -6091,7 +6091,8 @@ static ssize_t memory_high_write(struct kernfs_open_file *of,
char *buf, size_t nbytes, loff_t off)
{
struct mem_cgroup *memcg = mem_cgroup_from_css(of_css(of));
unsigned long nr_pages;
unsigned int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
bool drained = false;
unsigned long high;
int err;
@ -6102,12 +6103,29 @@ static ssize_t memory_high_write(struct kernfs_open_file *of,
memcg->high = high;
nr_pages = page_counter_read(&memcg->memory);
if (nr_pages > high)
try_to_free_mem_cgroup_pages(memcg, nr_pages - high,
GFP_KERNEL, true);
for (;;) {
unsigned long nr_pages = page_counter_read(&memcg->memory);
unsigned long reclaimed;
if (nr_pages <= high)
break;
if (signal_pending(current))
break;
if (!drained) {
drain_all_stock(memcg);
drained = true;
continue;
}
reclaimed = try_to_free_mem_cgroup_pages(memcg, nr_pages - high,
GFP_KERNEL, true);
if (!reclaimed && !nr_retries--)
break;
}
memcg_wb_domain_size_changed(memcg);
return nbytes;
}