On 6/3/23 4:53 AM, Shakeel Butt wrote:

On Fri, Jun 02, 2023 at 04:11:35PM +0800, Abel Wu wrote:

quoted

The status of global socket memory pressure is updated when:

   a) __sk_mem_raise_allocated():

	enter: sk_memory_allocated(sk) >  sysctl_mem[1]
	leave: sk_memory_allocated(sk) <= sysctl_mem[0]

   b) __sk_mem_reduce_allocated():

	leave: sk_under_memory_pressure(sk) &&
		sk_memory_allocated(sk) < sysctl_mem[0]

There is also sk_page_frag_refill() where we can enter the global
protocol memory pressure on actual global memory pressure i.e. page
allocation failed. However this might be irrelevant from this patch's
perspective as the focus is on the leaving part.

Leaving prot pressure or not under actual global vm pressure is
something similar to what you concerned last time (prot & memcg
is now intermingled), as this will mix prot & global together.

To decouple global info from prot level pressure, a new variable
might be needed. But I doubt the necessity as this seems to be a
rare case but a constant overhead on net core path to check the
global status (although can be relieved by static key).

And after a second thought, failing in skb_page_frag_refill()
doesn't necessarily mean there is global memory pressure since
it can due to the mpol/memset of the current task.

quoted

So the conditions of leaving global pressure are inconstant, which

*inconsistent

Will fix in next version.

quoted

may lead to the situation that one pressured net-memcg prevents the
global pressure from being cleared when there is indeed no global
pressure, thus the global constrains are still in effect unexpectedly
on the other sockets.

This patch fixes this by ignoring the net-memcg's pressure when
deciding whether should leave global memory pressure.

Fixes: e1aab161e013 ("socket: initial cgroup code.")
Signed-off-by: Abel Wu <redacted>

This patch looks good.

Thanks!
	Abel